troubleshooting, service tips, and major improvements for...

Troubleshooting, Service Tips, And Major Improvements ForHydrostatic Transmissions (Special Edition){3200}

943, 953, 963, 973 Loaders

Introduction

The hydrostatic transmissions used in 943, 953, 963 and 973 Loaders look quite different from powershift or direct drive transmissions. The hydrostatic transmission consists of a case, pump drive, headand top and bottom covers.

... The case contains the two axial piston pumps for the drive system. These pumps provide thehigh pressure oil for the motors that drive the tracks.... The pump drive housing is on the engine side of the case. Inside the pump drive housing arethe gears needed to transfer the power from the engine to the axial piston pumps.... The head is mounted on the front side of the case. The head, along with the charge and mainrelief valves that are mounted on it, works as a manifold system that directs the high pressureoil from the piston pumps to the motors. The head and valves also transfer the charge pump oilinto the drive circuit, between the piston pumps and motors and then out of the drive circuit tothe oil cooler.... On the top of the case is a cover. Under the cover are the valves and linkage that control thedisplacement (output) of the axial piston pumps.... The bottom cover of the case is the oil reservoir for the transmission system.

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Illustration 1. Typical hydrostatic transmission.

The filtering system for the transmission oil on these machines is different from the filtering systemsused with powershift and direct drive transmissions. With these transmissions the oil flows from theoil reservoir through a screen to the transmission pump. The oil goes from the pump to the filter andthen to the control valves. The filter has a bypass valve that lets unfiltered oil go to the control valveswhen the filter becomes plugged. This filtering system can permit debris to go on past the filter.

With the hydrostatic transmissions in these machines, the oil flows from the oil reservoir through thescreen and pump, like other transmissions. But, the oil then flows by a filter relief valve, through thefilter and on to the main control valve.

In this system the filter relief valve senses the pressure drop across the filter. When the filter becomesplugged, the filter relief valve sends the oil back to the oil reservoir. This keeps debris out of the restof the system, but it also decreases the flow of oil to the main control valve and the rest of thetransmission. As the oil flow to the main control valve decreases, venturi differential pressure lowersthe spool in the underspeed valve and the charge pressure decreases. The main control valve, sensingthis decrease in the charge pressure, applies the brakes. The lowered spool in the underspeed valvestrokes (moves) the axial piston pumps to a near zero angle which decreases the output flow andresults in lower drive pressure. This will prevent damage to any of the components from low chargepressure and flow caused by the filter relief valve sending oil back to the oil reservoir.

The filter relief valve is the core of the hydrostatic transmission filtering system. It keeps debris thatmay be in the reservoir, out of the valves, axial piston pumps and drive motors.

NOTICE

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Always drain the filter housing before the oil filter is removed. Failureto drain and clean the filter housing may contaminate the system.

The charge pressure oil in the axial piston pumps and drive motors will force any debris, that iscreated from a failure in these components, out into the oil reservoir or motor case. Because of thesefeatures, along with the automatic stroking back of the pumps when the charge pressure decreases toless than 860 kPa (125 psi), there is very little chance of contamination of the complete transmission.Therefore, it is not necessary to completely disassemble the hydrostatic transmission when there is afailure.

NOTE: If there is a failure, the port plates in the pumps and/or motors can be examined to determinethe extent of the contamination. If there are no scratches across the narrow sealing lands or betweenthe ports for the high pressure and low pressure sides, debris has not circulated through the valvesand the drive pressure system. For examples of this see the port plate section of "Guideline ForReusable Parts, Piston Pumps and Motors", Form SEBF8032.

Troubleshooting

General Information

The hydrostatic transmission system is a series of separate hydraulic and mechanical systems thatfunction together as a complete transmission system. The complete transmission system transmitspower from the engine to the final drives. Each of these separate systems has its own purpose orfunction within the transmission. They either transmit the power or control the amount of power thatis transmitted.

To make it easier and quicker to diagnose and locate problems, the complete transmission system isdivided into the following separate systems. These systems are connected in series. These separatesystems that make up the complete transmission are:

1. Charge pump and filter system.2. Underspeed and overspeed system.3. Operate/brake spool system.4. Servo control system.5. Piston pumps, motors and relief systems.6. Transmission oil cooler system.7. Two speed motor shifting system (973 Loaders only).

Charge Pump And Filter System

The charge pump and filter system consists of:

a. Suction screen (1).b. Charge pump (2).c. Filter relief valve (3).



d. Filter (4).e. Venturi (5).f. Underspeed cut-in adjustment screw and plunger (venturi bypass)

The purpose of this system is to provide oil flow to the other systems.

The operating condition of this system can be determined by checking the venturi differential pressure(difference between venturi upstream pressure and venturi throat pressure). This differential pressurecan be used to determine if there is sufficient flow going from this system to the remainder of thetransmission to allow it to operate correctly. A venturi differential pressure that is less than thespecification indicates a problem in this system.

Any malfunction in this system will affect the operation of both tracks equally since it provides flowfor all other systems.

Illustration 2. Charge pump and filter system.

Underspeed And Overspeed System

The second system in the series is the underspeed and overspeed system which consists of:

a. Underspeed valve (6).b. Underspeed override valve (7).c. The land of the operate/brake (formerly called operate/vent) spool in the main control valve.d. The underspeed lowering portion of the speed/brake valve stem in the main control valve.e. The smaller diameters steel tubes and fittings under the top cover.f. The mechanical linkage from the transmission control lever in the cab through the underspeedvalve to the linkage rod end on the direction speed link (8).g. Quick response valve (9).h. Overspeed valve (10).i. Venturi throat orifice.



The purpose of this system is to automatically control the output flow of the axial piston pumps. Itcontrols both pumps simultaneously.

The operating condition of these valves, spools and lines can be determined by the differentialpressure (upstream pressure minus throat pressure) of the underspeed valve. The underspeed upstreamand throat pressures can be checked at the two quick disconnects on top of the main control valve. Ifthe differential pressure of the underspeed valve is within the specification and there is no movementof the tracks, the problem is in the mechanical linkage of the system.

This system, like the first system, affects the operation of both tracks equally.

Illustration 3. Underspeed and overspeed system.

Operate/Brake Spool System

This system consists of:

a. Charge pressure check valve (11).b. Start vent spool (12).c. Operate/brake spool (13).d. Speed/brake valve stem (14).e. Pilot valve (15).f. Orifice to the pilot valve (16).g. The linkage for the center pedal.

The purpose of this system is to control the shifting of the operate/brake spool.

To check the operating condition of the system, measure the pressure at the plug on the top left end ofthe main control valve with the transmission control lever in the BRAKES OFF (formerly Reset)position. This pressure can be used to determine the operation of the components. If this pressure isapproximately the same as the charge pressure, the system is functioning correctly. The pressuregoing to this plug also controls the portion of the operate/brake spool that is a part of the Underspeedand Overspeed System. If the difference between underspeed upstream and throat pressure is low, thepressure at the plug on the top left end of the main control valve can be used to determine if theoperate/brake spool is the cause of the problem. Pressure checks at the other plugs on top of the maincontrol valve can be used to determine if there are problems with any of the other components in thissystem. (See the article "Loader Will Not Move; Plugged Orifice In Main Control Valve Can Be



Backflushed", in the Main Control Valve, Overspeed And Pilot Valve, Underspeed Valve section ofthis publication.)

This system will also affect the operation of both tracks equally.

Illustration 4. Operate/brake spool system.

Servo Control System

The fourth system is the servo control system. This system consists of:

a. Servo relief valve (17).b. Servo valves (18).c. Servo cylinders and lines (19).d. Sync screws (20).e. Neutral screws (21).f. Sync link (22).g. Steering pedals and linkage.h. Cardan joints.

The purpose of this system is to provide both synchronized and independent control of the output flowfrom the axial piston pumps. This system keeps the machine moving straight and provides the steeringof the machine.

The operation of this system can be determined by checking: the servo relief valve setting, the drivepressures for "Low Forward" and "Low Reverse" as shown on the Data Sheet, and an operationalcheck of the machine with the sync cutoff valve closed. Mechanical checks of the adjustment of thesteering linkage, internal linkage, and sync screws can be made.

A malfunction of this system will not affect the operation of both tracks equally. If the machine doesnot travel in a straight line or only the left track continues to rotate when loading the bucket, themalfunction is probably in this system.



Illustration 5. Servo control system.

Piston Pumps, Motors, And Relief System

This system consists of:

a. Axial piston pumps (23).b. Drive motors (24).c. Charge and main relief valves (25).d. Charge pressure relief valve (26).e. Sync cutoff valve (27).f. Sync valve (28).

The purpose of this system is to provide makeup oil under pressure to the drive circuit, provideprotection for the drive circuit, and transfer the engine power to the final drives.

The tests which follow can be made to check the operation of this system:

... Check the charge pressure relief valve in PARK, BRAKES OFF, max FORWARD stall andmax REVERSE stall.... Check the case drain pressure for each motor.... Check the drive pressures while in a maximum stall condition.



... Check the machines ability to run straight and turn correctly with the sync cutoff screw in thecutoff position and then test again with the screw opened three turns.

A low charge pressure reading indicates a faulty charge relief valve or a leak in one of the pistonpumps or motors. A motor case drain pressure, that is higher than specification, indicates that themotor has excessive leakage and is in need of repair.

A low charge pressure relief valve setting will usually affect the operation of both tracks equally. Afailure of a motor can affect the operation of one or both of the tracks. A low drive system pressurewill usually be caused by either the drive relief valve for that side or the servo system and will affectthe operation of only one track.

A malfunctioning drive system relief valve will not cause a low charge relief pressure, because the oilfrom the low pressure side of the drive relief valve is combined with the charge system oil before itpasses through the charge relief valve.

Illustration 6. Piston pumps, motors, and relief system.

Transmission Oil Cooler System

The transmission oil cooler system includes:

a. Oil cooler bypass valve (29).b. Oil cooler return screen which is located in the bottom cover (30).c. Oil cooler (31).

The purpose of this system is to keep the transmission oil temperature within the operating range,limit the system back pressure from the oil cooler and to return the oil to the reservoir withoutcreating aeration.

Pressure checks can be made at the inlet and outlet of the oil cooler to determine the condition of theoil cooler tubes and the return screen. The back pressure at either of these locations must not exceed310 kPa (45 psi) with the oil at a minimum temperature of 32°C (90°F).



A check, using a flow meter at the transmission oil cooler inlet, can be made to determine thecondition of the oil cooler bypass valve. Use the procedure which follows:

1. Check the oil cooler flow at high idle rpm in PARK.

2. If the cooler flow is low and the back pressure at the flow meter is less than 310 kPa (45 psi), installa spacer behind the bypass valve to keep the valve closed.

3. Check the oil cooler flow at high idle rpm in PARK.

4. If the oil flow is now within the specifications and the back pressure is still less than 310 kPa (45psi), then the oil cooler bypass valve is faulty.

If the oil flow is within the specifications, but the back pressure goes above 310 kPa (45 psi), then thecooler bypass valve is faulty and either the oil cooler is internally plugged or the return screen isplugged. Pressure checks can be made to determine which one is plugged.

A malfunction of this system will always be indicated by overheating of the transmission. The mostlikely causes of transmission overheating are:

... Restriction of air flow through the oil cooler core.

... Plugged tubes inside the oil cooler core.

... A plugged return screen.

... A faulty oil cooler bypass valve.

Illustration 7. Transmission oil cooler system.

Two Speed Motor Shifting System (973 Loaders Only)

The two speed motor shifting system consists of:



a. Control valve for two speed motor (32).b. Lines from control valve to motors.c. Orifice fittings on the motors (33).d. Piston and trunnion in the motor (34).

The purpose of this system is to provide shifting of the motors to either a high speed, low torque orlow speed, high torque position as determined by the pressure in the high pressure circuit.

To check the operation of the control valves, do the following steps.

1. Turn the sync cutoff valve adjustment screw completely in.

2. Slowly stall the transmission.

3. Check the pressures at the quick disconnect for the shifting piston on the right motor and at thedrive pressure quick disconnect on the sync valve. The shifting piston pressure should start to dropwhen the drive pressure reaches 22 750 kPa (3300 psi).

The condition of the orifice and lines can be determined by checking the amount of time it takes theshifting pressure to return to normal after a shift. It should take approximately four seconds for thepressure to return to normal.

Illustration 8. Two speed motor shifting system.

Use of the Transmission Troubleshooting Data Sheet

General Information

The Transmission Troubleshooting Data Sheet should be used to record data when tests are made onthe hydrostatic transmission. Use the 6V4157 Transmission Testing Group, the 6V3121 MultitachGroup and the 8T470 Thermistor Thermometer Group for these tests. The actual machine data, when

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compared to the data in the chart, will help to determine what the problem is, where the problem isand possibly what is needed to correct the problem. Because some of the specifications in the DataSheets change, always use the most current Data Sheet for your machine.

The information which follows gives a brief explanation of the different tests that can be made andhow to interpret the results. Remember, when the relief valves are correctly adjusted, pressure shouldbe within the Data Sheet specifications regardless of the oil temperature. It can be expected that thereadings will be on the high side of the tolerance with cool oil and on the low side of the tolerancewith 80°C (175°F) oil.

The cooler flow readings are not normally needed to analyze problems in the transmission. Thecharge pressure is generally a good indication of the oil cooler flow. Oil cooler flow readings arenecessary to determine if a charge relief valve is working correctly. If the oil cooler flow is withinspecifications and the charge pressure is low during full FORWARD or full REVERSE testconditions, make an adjustment to the charge pressure relief valve. If it can not be adjusted to thespecifications during all test conditions, replace it.

Test 1. Transmission Control Lever In PARK Position.

The temperature of the transmission oil must be kept within the specification shown to get accuratedata. If the oil is not at the correct temperature during the tests, the data obtained may not be accurate.Some problems will only be apparent at the correct test temperature. The Service Manual has thecorrect procedure to use to get the oil temperature up to the specification.

The engine speed (rpm) must also be kept within the specification shown for the obtained data to beaccurate. If the engine speed is out of the specification, it can effect the output of the pumps and thesystem pressures. If engine speeds are out of the specification, use a 6V4060 Engine Set PointIndicator Group and make an adjustment to the engine speeds.

In the PARK position, the drive pressure must be the same as the charge pressure.

NOTE: It may be difficult to read the drive pressure on the 52 000 kPa (7500 psi) gauges but someindication should be present. If there is no indication at all, check the gauges. If the pressure is higherthan 1380 kPa (200 psi), make an adjustment to the neutral screw for the side that is higher.

Next, record the venturi upstream and throat pressures. Subtract the throat pressure from the upstreampressure. Write down the difference. This is the differential pressure. It must be within thespecification shown.

Because there can be wide variations in the venturi pressures, comparative data is only given for thedifferential pressure. The differential pressure is a direct indication of the flow through the venturi. Ifthe differential pressure is low, there is not enough flow through the venturi and there is a problemupstream of the venturi.

Check the charge pressure and then the servo supply pressure. If the charge pressure is low and thedifferential pressure is correct, the problem is in the charge relief valve or there is a leak in one ormore of the pump or motor groups.

Check the brake pressure and the case drain pressures for the two drive motors. In PARK, the brakepressure must always be zero. If it is not zero, it is an indication that either the operate/brake spool inthe main control valve is stuck in the open position or the pilot valve is not working correctly.



Before the case drain pressures are checked, either remove the filler cap on 943 and 953 Loaders orremove the plug in the top cover on 963 and 973 Loaders. This will relieve any pressure in thetransmission. The case drain pressure for the drive motors should be zero. However, because of therouting of the case drain line from the right drive motor, its pressure may be as much as 14 kPa (2.0psi). If the pressure in either drive motor is higher, decrease the engine rpm to 1500 rpm. If thepressure is still high, there is a problem in the motor.

Test 2. BRAKES OFF Position.

Very carefully move the transmission control lever to the BRAKES OFF position. This can be ineither FORWARD or REVERSE but it must not cause the drive pressures to increase or the enginerpm to decrease by more than 50 rpm. As the control lever is moved (forward or reverse) from thePARK position, the spool in the pilot valve moves to close a passage to the tank. When the passage tothe tank is closed, the operate/brake spool shifts to allow oil pressure to release the brakes and activatethe underspeed valve. This puts the drive system in a condition where further movement of the controllever will cause the machine to move. The only other differences between the PARK and BRAKESOFF positions are an increase in brake pressure to a pressure that is 0 to 70 kPa (0 to 10 psi) less thancharge pressure and a small increase in cooler flow.

Transmission Troubleshooting Data Sheet



Transmission Troubleshooting Data Sheet



On machines equipped with a U-TUBE, if the brake pressure is more than 70 kPa (10 psi) belowcharge pressure, move the U-TUBE to the TOW position and start Test 2 again. This low brakepressure could be an indication of leakage through the hand pump.

Tests 3 and 5. Maximum FORWARD and REVERSE Positions.



When the transmission control lever is pulled into the maximum FORWARD or REVERSE position,engine rpm will decrease but must be within the specification shown on the Data Sheet.

Cooler flow will decrease because most of the flow is being used to makeup for losses in the drivecircuits and because the charge pump rpm has decreased along with the engine rpm.

Drive pressure will increase to 38 000 kPa (5500 psi) between the oil temperature range of 49° to 65°C (120° to 150°F). When the oil temperature is between 76°C (170°F) and 82°C (180°F), the drivepressure will be approximately 36 000 kPa (5200 psi). Do not attempt to adjust this setting. If it isadjusted higher and the oil gets cooler, higher pressures would occur if the drive loop is stalled. Thiscould result in damage to the system.

The differential pressure will decrease to as low as 700 kPa (100 psi) and the charge pressure will beapproximately 1000 kPa (150 psi). The charge pressure should not be less than 860 kPa (125 psi). Ifthe charge pressure is less than 860 kPa (125 psi), it will allow the operate/brake spool to moveenough to apply the brakes and lower the underspeed valve spool. This will cause a cycling of thetransmission pumps during testing. If the charge pressure is less than 730 kPa (106 psi) for longerthan two seconds, it will allow the start/vent spool to move enough to vent the transmission. Thetransmission control lever must then be returned to PARK to reset the transmission.

When the transmission lever is moved from PARK to maximum FORWARD or maximumREVERSE, the servo supply pressure can decrease 172 to 207 kPa (25 to 30 psi), but normally it willnot decrease more than 70 to 100 kPa (10 to 15 psi). If the servo supply pressure decreases more than207 kPa (30 psi) between PARK and maximum FORWARD or maximum REVERSE position, it isan indication of contamination in the servo supply relief valve.

The case drain pressures for the drive motors should still be zero when the transmission lever ismoved to maximum FORWARD or REVERSE. If the pressure for either side exceeds 14 kPa (2.0psi) in the maximum FORWARD or REVERSE position, there is a leakage problem in one of themotors that must be corrected.

Troubleshooting Guide

Use extreme care while doing the following test and adjustments. It ispossible under conditions of wear for the track brakes to slip and let the

machine move. See Procedure for Testing Brakes in the appropriateService Manual before doing any tests or adjustments.

NOTICE

The U-TUBE, if so equipped, must be in the test position or the hosefrom the transmission to the brake manifold must be plugged on later



machines when making the pressure and flow tests in the followingproblems.

PROBLEM-Machine Will Not Move When The Transmission Lever Is Moved Into FORWARDor REVERSE (Engine at high idle rpm and not lugging).

Test 1. Check venturi pressure differential (venturi upstream pressure minus venturi throat pressure).

- If pressures are zero, check the following.

* No oil in the transmission.* Damaged charge pump.* Damaged charge pump drive shaft.* Filter relief valve not installed.

- If differential pressure is less than 1135 kPa (165 psi), the problem must be upstream of theventuri. Do Test 2.- If differential pressure is greater than 1135 kPa (165 psi), do Test 3.

Test 2. Check filter pressure differential (charge pump pressure minus venturi upstream pressure).

- If filter pressure differential is less than 170 kPa (25 psi), check the following.

* Filter relief valve held open.* Damaged O-rings on venturi.* Underspeed cut-in adjustment.* Worn charge pump.* Aeration or cavitation caused either by plugged suction line or screen.

- If filter pressure differential is greater than 170 kPa (25 psi), check the following.

* Filter plugged.* Viscosity of oil too high or oil is not at the correct temperature.

Test 3. Check charge pressure at high idle rpm in PARK.

- If charge pressure is less than 1270 kPa (185 psi), do Test 4.- If charge pressure is greater than 1270 kPa (185 psi), do Test 8.

Test 4. Check motor case drain pressures (943, 953 remove filler cap; 963, 973 remove plug in topcover).

- If a motor case drain pressure is greater than 70 kPa (10 psi), the motor is damaged on the sidethat is greater than 70 kPa (10 psi).- If the motor case drain pressure is 14 to 35 kPa (2 to 5 psi), the motor lube tube is worn.- If the motor case drain pressure is less than 14 kPa (2 psi), do Test 5.

Test 5. Check oil cooler flow.



- If oil cooler flow is greater than the specification, the charge relief valve is either out ofadjustment or damaged.- If oil cooler flow is less than the specification, do Test 6.

Test 6. Check filter for contamination with steel or bronze.

- If contaminated with steel or bronze, check for a damaged transmission pump.- If there is no contamination, do Test 7.

Test 7. Check the back pressure to the flowmeter.

- If the back pressure is less than 310 kPa (45 psi), check for leaks at either the oil cooler bypassvalve or in the transmission.- If the back pressure is greater than 310 kPa (45 psi), correct the back pressure and test again.

Test 8. Move transmission lever to BRAKES OFF (Reset) position. Check the charge and brakepressures. Brake pressure should be 0 to 70 kPa (0 to 10 psi) less than charge pressure.

- If the brake pressure is correct, do Test 12.- If the brake pressure is zero, do Test 13.- If the charge pressure is less than 1000 kPa (145 psi) or the brake pressure is more than 35 kPa(5 psi) below charge pressure.

* Damaged hand pump check valve.* Hoses to hand pump may be crossed.* Move the U-TUBE to TOW position and test again.* If none of the above solves the problem, do Test 9.

Test 9. Check the motor case drain pressures (943, 953 remove filler cap; 963, 973 remove plug intop cover).

- If a motor case drain pressure is greater than 35 kPa (5 psi), the motor is damaged on the sidethat is greater than 35 kPa (5 psi).- If motor case drain is 14 to 35 kPa (2 to 5 psi), the motor lube tube is worn.- If the motor case drain pressure is less than 14 kPa (2 psi), the motors are in good condition.Do Test 10.

Test 10. Check the filter for contamination with steel or bronze.

- If the filter is contaminated with steel or bronze, check for a damaged transmission pump.- If there is no contamination, do Test 11.

Test 11. Check the oil cooler flow in maximum FORWARD and REVERSE positions.

- If the oil cooler flow is greater than the specification, the charge relief valve is either out ofadjustment or damaged.- If the oil cooler flow is less than the specification, check the transmission for leaks whilerunning with top cover removed.

Test 12. Check the underspeed pressure differential at the top of the main control valve (underspeedupstream pressure minus underspeed throat pressure) with the transmission lever moved to BRAKESOFF position.



- If the underspeed pressure differential is less than 1030 kPa (150 psi), check the following.

* Operate/brake spool does not move completely to the right side.* Check for sticking or damaged quick response valve.* Lines to underspeed valve under top cover are loose or damaged.

- If the underspeed pressure differential is greater than 1030 kPa (150 psi), check themechanical linkage under the top cover.

Test 13. Make sure center pedal adjustment is correct. The bolt must go through the hole in the leverinto the threaded hole in the valve. In the BRAKES OFF position, check the pressure to the top leftplug in the main control valve.

- If the pressure is greater than 860 kPa (125 psi), check for debris blocking the operate/brakespool.- If the pressure is less than 860 kPa (125 psi), do the following:

* Back flush orifice. (See the article "Loader Will Not Move; Plugged Orifice In MainControl Valve Can Be Backflushed" in the Main Control Valve, Overspeed and PilotValve, Underspeed Valve section of this publication).* If this does not solve the problem, do Test 14.

Test 14. Remove the top right plug in the main control valve and check the flow while in PARK.

- If the flow is less than 30 mL/min (1 oz/min), the plug under the spring is good.- If the flow is greater than 30 mL/min (1 oz/min), the plug under the spring is loose or hascome out of position.

PROBLEM-Machine Moves Slowly at High Idle RPM, Ground Speed Increases as GovernorControl is Moved Toward Low Idle RPM.

Test 1. Check venturi pressure differential (venturi upstream pressure minus throat pressure) at highidle rpm.

- If venturi pressure differential is less than 1135 kPa (165 psi), do Test 2 of the Problem-"Machine will not move when the transmission lever is moved into FORWARD orREVERSE."- If venturi pressure differential is greater than 1135 kPa (165 psi), do the following Test 2.

Test 2. Check the underspeed pressures taken at the top of the main control valve with thetransmission lever in the BRAKES OFF position.

- If underspeed upstream pressure is more than 280 kPa (40 psi) less than venturi upstreampressure and underspeed throat pressure is the same as venturi throat pressure, check forleakage in lines to underspeed valve under the top cover.- If underspeed throat pressure is greater than venturi throat pressure, do Test 3.

Test 3. Check center pedal adjustment.

- If pedal adjustment is incorrect, make the correct adjustments.- If pedal adjustment is correct, do Test 4.



Test 4. Disconnect underspeed override valve and fasten it fully open. Operate the engine at high idlerpm, three-fourths high idle rpm and one-half high idle rpm with the transmission lever moved toBRAKES OFF position. Record the venturi throat pressure and the underspeed throat pressure at eachof these speeds.

- If the underspeed throat pressure remains consistently higher than the venturi throat pressureat all rpms, the quick response valve may be sticking open.- If the underspeed throat pressure and the venturi throat pressure readings are the same at thelower engine rpms, do Test 5.

Test 5. Turn overspeed valve adjustment screw in until it bottoms out. Check underspeed pressuredifferential with transmission lever in the BRAKES OFF position.

- If underspeed pressure differential is greater than 1030 kPa (150 psi), adjust overspeed valve.- If underspeed pressure differential is less than 1030 kPa (150 psi), do Test 6.

Test 6. Check operate/brake spool for full movement to right side.

- If there is complete movement, check quick response valve.- If movement is restricted, correct the problem.

PROBLEM-Machine Will Not Track Straight in FORWARD and REVERSE.

Test 1. Check steering pedal linkage adjustment.

- If the linkage is out of adjustment, correct the problem.- If the adjustment is correct, do Test 2.

Test 2. Check motor case drain pressures. (943 and 953 remove filler cap; 963 and 973 remove plugin top cover).

- If the motor case drain pressures are greater than 35 kPa (5 psi), the motor is damaged on theside that is greater than 35 kPa (5 psi).- If the motor case drain pressures are less than 14 kPa (2 psi), check the following.

* Check the final drives for possible damage.* If the problem is not in the final drives, do Test 3.

Test 3. Do a drift test with sync valve cutoff screw turned in.

- If the machine moves in "S" pattern, adjust the neutral screw.- If the machine moves in REVERSE when lever is first pulled to FORWARD or movesFORWARD when lever is first pulled to REVERSE, check the following.

* Servo cylinder not pinned in head.* Servo cylinder lines either loose or disconnected.* Damaged seals in servo cylinder. Disconnect lines and check with air pressure.* Servo valve stem and spool not a matched set. Check serial numbers on the stem andthe spool.* Damaged Cardan joint.

- If the machine moves in a "C" pattern, do Test 4.



Test 4. Check drive pressures.

- If the drive pressures are correct, adjust the sync screw. (Whatever track is the fastest, turn itssync screw clockwise.)- If the drive pressures are either less than 35 880 kPa (5200 psi) or greater than 40 050 kPa(5800 psi), adjust the drive pressure relief valve.

New Procedure To Remove And Install Transmission HeadAnd Barrel Assemblies

The Service Manuals show correct procedures for removing the head and disassembling the axialpiston pumps. These procedures contain some extra steps that are not needed when only the headand/or barrel assemblies are to be removed.

The following is a recommended method that is being used by several dealers to repair hydrostatictransmissions that have axial piston pump failures. This method greatly reduces the time required forthese repairs. There will be little or no need for adjustments after the repair.

The procedure which follows shows a hydrostatic transmission from a 953 Loader. This procedurecan also be used as a guide for the transmissions in 943, 963 and 973 Loaders. Use the ServiceManual along with this new procedure. Before this new procedure can be done, a modification mustbe made to the FT1501 Adapter Bracket Assembly. Remove 43.1 mm (1.70") from the end of thebracket assembly as shown in the illustration.

Modification to FT1501 Adapter Bracket Assembly.

Fabrication Of FT1769 Lifting Bracket

The FT1769 Lifting Bracket makes the removal of the transmission head assembly much easier. Withthe lifting bracket, the transmission head can be removed without the removal of the charge and reliefvalves or the charge pump. The lifting bracket connects to the charge and relief valves at the samelocation that the upper oil lines for the track motors are connected.



All the pieces of the FT1769 Lifting Bracket should be fabricated from SAE 1018 steel. Items 1, 2and 4 are made from 12.7 mm (.50") diameter bar stock. Make two each of Items 1 and 3 and oneeach of Items 2 and 4 for each lifting bracket. To make alignment of the bolt holes easier, fasten Items3 to the charge and relief valves. Then put Item 4 in position and tack weld Item 4 to Items 3.

FT1769 Lifting Bracket.



Removal Of Head And/Or Barrel Assemblies

1. Remove hydrostatic transmission (1) and install it on a repair stand. See Illustration 1.

Illustration 1.

2. Remove the bolts and tube assembly (2) that connect the charge pump to the oil pan. SeeIllustration 2.

Illustration 2.

3. Remove the bolts that hold manifold (3) to the charge pump. See Illustration 3.



Illustration 3.

4. Remove the bolts that hold oil filter housing (4) in place. Remove the oil filter housing andmanifold as a unit.

5. Disconnect the upper end of hose assembly (5). See Illustration 4.

Illustration 4.

6. Remove or disconnect any tubes or hoses that connect the head to the transmission case.

7. Remove plugs (6) and the springs that hold the anchor pins for the servo cylinders. See Illustration5.



Illustration 5.

8. Fabricate a 6.4 mm (.25") x 50 mm (2.0") x 102 mm (4.0") steel plate (7) with a 20.50 mm (.813")diameter hole in the center. See Illustration 6.

Illustration 6.

9. Install the fabricated plate on the end of the transmission drive shaft using a 3/4"-10 bolt that willbottom out in the drive shaft and allow the plate to rotate freely.

10. Install the FT1769 Bracket on the head. Fasten a hoist to the FT1769 Bracket.

Large springs in the pump barrels are held in compression by the head.The head can be pushed away from the case very rapidly. To avoid

personal injury, the spring tension must be released before the last boltis removed from the head. To gradually release the spring tension, besure the head moves away from the case as the bolts in the head are



loosened. The bolts in the head are long enough to release all of thetension in the springs before the bolts are removed.

11. Evenly loosen the bolts that hold the head to the transmission case. There is spring force on thehead. Remove the bolts that hold the head in place.

12. Pull the head away from the transmission far enough to remove the anchor pins.

13. Use 6V7857 Slide Hammer and remove the anchor pins.

NOTICE

When the head is removed, do not let the port plates fall from the head.The port plates are made of bronze and are easily damaged. Give extraprotection to both sides of the port plates and the surface of the head

that comes in contact with the port plates.

14. Remove the head from the transmission. Make sure the port plates are not dropped when the headis removed.

NOTE: Do the steps which follow, only if it is necessary to remove the barrel assemblies.

15. Put a protective plate in position on the surface of the barrel to prevent damage to the barrel. (Seethe Service Manual for the correct tools for the different models).

16. Install the bearing puller and remove bearing (8). See Illustration 7.

Illustration 7.

17. Remove barrel assembly (9) from the swashplate and pistons. See Illustration 8.



Illustration 8.

Installation Of Head And/Or Barrel Assemblies

1. Put the transmission in position as shown in Illustration 9.

Illustration 9.

2. Move the servo cylinder so that the swashplate is at the maximum angle.

3. Attach rope (10) to the barrel assembly in two places.

NOTE: It is not necessary to install the pistons in their original bores.

4. Lower the barrel assembly on to the highest projecting piston and install it in the barrel assembly.Continue to lower the barrel assembly and install the pistons one at a time.

5. Heat the bearing cones to a maximum temperature of 120°C (248°F) and install them on the shafts.

6. Rotate the transmission so the mounting surface for the head is in a vertical position.

7. Pull the head end of the servo cylinder away from the transmission. Use a pair of vise grips (11) tohold each servo cylinder in place. See Illustration 10. Both servo cylinders must be held away fromthe transmission before installing the head.



Illustration 10.

8. Install guide bolts in the transmission case. Use FT1769 Lifting Bracket (12) to put head (13) inposition. See Illustration 11. As the head is put in position, align the pin bores in the ends of the servocylinders with the corresponding bores in the head. Install anchor pins (14) with the threaded holetoward the top. See Illustration 12.

Illustration 11.

Illustration 12.

9. Install the springs and plugs that hold the anchor pins in place. Remove the vise grips.



10. Now install the head. As the head is installed, rotate the drive shaft using the bolt that wasinstalled earlier. This will make it easier to align the splines on the charge pump shaft with the splineson the drive shaft. It will also keep the bearings on the ends of the pump shafts in alignment with theircups.

NOTE: If desired, remove the charge pump from the head before the head is installed. Install thehead on the transmission case and then install the charge pump on the head.

11. Install the bolts that hold the head in place. See the appropriate Service Manual for the correcttorque and sequence. Remove the FT1769 Bracket from the head.

12. Remove the bolt and fabricated plate from the transmission drive shaft.

13. Install the oil filter housing and manifold.

14. Install all hoses and tubes.

15. Install the hydrostatic transmission.

Service Tips And Major Improvements

Charge Pump and Filter

Service Tips

Make Sure The Correct Oil Is Used In Hydrostatic Transmissions

Reports show that high viscosity oil has been used in some hydrostatic transmissions. Only SAE 5W-20 or 10W oil should be used in these transmissions. If higher viscosity oil is used, it can damage theoil filters, hold the filter relief valve open until higher oil temperatures are reached, and cause themain control valve to give incorrect signals to the underspeed system.

Servo Relief Valve Failure; Transmission Filter Inspection And Change Procedure

There have been reports of failures of the transmission servo relief valve. Some of these servo reliefvalves failed after the transmission oil filter had been removed for service or inspection.

These failures are some times caused by debris that has formed sediments at the bottom of the filterhousing. This debris can fall to the bottom of the filter housing and be flushed into the system.

Later loaders, and machines with modifications made to the oil filter housing, have a plate and a drainline in the bottom of the filter housing. On these later machines, remove the drain line plug and drainthe oil from the filter housing before the oil filter element is removed. After the filter element hasbeen removed, be sure to look for debris on the plate. Clean the plate to remove any debris before thefilter element is installed.

Because the earlier loaders do not have the improved housing, it is very important to clean thehousing when the filter element is removed. Clean and visually inspect the housing to be sure there isno debris before installation of a new filter element.



Major Improvements

New Transmission Charge Pump Has More Capacity; Identification Of Units With New Pump963 Loaders

DESCRIPTION OF CHANGE: A new charge pump is used in hydrostatic transmissions for 963Loaders. The new pump has more capacity than the former pump, to increase the rate of flow throughthe cooler. This improves the cooling for better performance and longer service life.

ADAPTABLE TO: All earlier machines when the necessary parts are used together. See the partschart. The recommendation is to install the new pump any time replacement of a former pumpbecomes necessary, and put a mark on the transmission identification plate. See the topic"Identification".

IDENTIFICATION: For identification of transmissions equipped with the 3G2185 Pump Group, a"-5" mark is put after the serial number on the transmission identification plate with metal stamps.While Parts Microfiche and the NPR (Numerical Parts Record) show the new pump used inhydrostatic transmissions with Serial Numbers 4TA325-Up, some earlier transmissions have the "-5"mark after the serial number. For this reason, be sure to look for the mark as a positive identificationduring transmission service. Also, be sure to add the "-5" mark to the transmission identification platewhen the new 3G2185 Pump Group is installed in any earlier transmission.



Location of new parts in hydrostatic power case group.

Transmission Filter Improved; Drain Line Added For Easier Service

DESCRIPTION OF CHANGE: A drain lines group has been added to the power train arrangementfor these machines. At the same time, the filter group for the hydrostatic transmission is changed forinstallation of the drain line and improved performance.

NOTE: A later article that announced changes to the drain lines group has been included with thisarticle.

Some components of the drain lines groups have changed. The former drain lines groups had a plug atthe outlet end of the drain hose. During machine operation, it was possible for a hole to be worn in thedrain hose. This would cause the loss of transmission oil and cause a machine shutdown.

The new drain lines groups have a valve that is mounted on the filter housing. This will keeptransmission oil out of the drain hose until the valve is opened.

There are two primary changes to the filter group. One is the addition of a hole at the front near thebottom of the housing for the drain line connection. The other change is removal of the support (rod)formerly used to hold the lower plate and the filter element to the cover assembly. A new coverassembly has only a short pin to hold the upper plate assembly and spring to the cover. The lowerplate is now fastened to the bottom of the housing with a new bolt, washer and spring. A new plug inthe bottom center hole of the housing has threads for this new bolt. The space around the lower platewill keep more of the dirt and sediment in the bottom of the housing, away from the clean oil. Thesechanges will improve filter performance, and make filter service easier.

ADAPTABLE AS: The new and former parts for the filter group are shown in Chart A and are ineffect as shown in Chart B. The new and former parts for the drain lines groups are shown in Chart C.



MODIFICATION OF FILTER HOUSING: Earlier filter groups can be changed to the new designas follows:

1. Remove the complete filter from the machine as a unit.

2. Disassemble the filter.

3. Machine the new hole in the housing as shown in Illustration 1.



Illustration 1. Dimensions to machine filter housing.

4. Remove the 3K6060 Nut, 3G1875 Plate, and the element from the support (rod) of the coverassembly.

5. Remove the 3B4617 Cotter, 4B4280 Washer, 3G1873 Plate Assembly, and 2J4045 Spring from thecover support (rod). Release the spring gradually, and be careful to prevent damage to the seal in theplate assembly.

6. Cut off the support (rod) of the cover assembly 12.7 mm (.50") below the hole for the cotter. Grindthe end smooth, with a bevel to prevent damage to the seal in the plate assembly during installation.

7. Assemble the parts removed in Step 5.

8. Thoroughly clean all parts to remove any metal chips or particles.

9. Install a new 4T2638 Plug in place of the former 9S9334 Plug in the center hole in the bottom ofthe housing.

10. Put the 3G1875 Plate in position in the bottom of the filter housing. Assemble the 5M2894Washer (first) and 4B7033 Spring on the 6V5804 Bolt, then install the bolt through the 3G1875 Plateand into the 4T2638 Plug. Tighten the bolt to a torque of 50 ± 7 N·m (37 ± 5 lb ft).

NOTE: Illustration 2 shows the locations of the new parts in the filter group. After the modificationin Step 6, the former cover assembly is basically the same as the new cover assembly.



Illustration 2. Filter group parts.

11. Install the 307948 Elbow, with the 3K360 Seal, in the new hole in the housing (Step 3). These areparts of the drain lines group.

12. Install the filter housing on the transmission and connect the 8G5494 Hose Assembly (drain line)to the 307948 Elbow. Also install the 5P2909 Plug in the other end of the hose assembly.

13. Install a new element, fill the filter with clean oil, and install the cover.

NOTICE

With this change in filter design, the 3G1875 Plate is not removed withthe cover and element during normal filter service. For this reason, it

will be necessary to check for any debris or foreign material on theplate, and clean it as needed at all future filter changes. The plug, if soequipped, must be removed from the hose and the oil drained before

removal of the filter element.

INSTALLATION PROCEDURE FOR 943 AND 953 LOADERS

1. Remove the existing drain hose and fittings from the transmission oil filter housing. See Illustration3.

2. Install the 3K360 Seal and 6V7238 Valve (1) on filter housing. Be sure the outlet of the valvepoints down.

3. Install 160 cm (63") of 5P743 Hose (2) on valve (1). Use a 5D1026 Clamp (3) to fasten the hose tothe valve.



4. Remove the lower front guard. Route drain hose (2) out to the lower front guard.

5. Use two 7K1181 Straps (4) to fasten drain hose (2) to the hydraulic tank drain hose as shown inIllustration 3.

NOTE: Be sure there are no sags in hose (2) between Points A and B.

6. Install the center bottom guard and the lower front guard. Add oil to the transmission to replace thatwhich was drained from the filter housing. Lower the cab.

Illustration 3. Location of drain lines for transmission oil filter housing on 943 and 953 Loaders.

INSTALLATION PROCEDURE FOR 963 LOADERS


2. Install the 3K360 Seal and 6V7238 Valve (5) on the filter housing. Be sure the outlet of the valvepoints down.

3. Install 210 cm (82.7") of 5P743 Hose (8) on valve (5). Use a 5D1026 Clamp (9) to fasten the hoseto the valve.

4. Route drain hose (8) to the rear access cover in the rear bottom guard.

5. Remove two bolts from the transmission oil pan at the locations shown. Install two 8J8197 Clips(7) on drain hose (8) and fasten the clips (7) to the transmission oil pan with bolts removed earlier.


6. Install 8J8197 Clip (7) on drain hose (8). Remove a frame bolt in the area shown. Use the bolt tofasten clip (7) to the frame.

7. Install 7D7233 Clip (6) on the drain hose. Fasten clip (6) to the rear main frame crossmember witha 5P1075 Washer (11) and S509 Bolt (10).

8. Install the center bottom guards. Add oil to the transmission to replace that which was drained fromthe filter housing. Lower the cab.



Illustration 4. Location of drain lines for transmission oil filter housing on 963 Loaders.

INSTALLATION PROCEDURE FOR 973 LOADERS


2. Install the 3K360 Seal and 6V7238 Valve (12) on the filter housing. Be sure the outlet of the valvepoints down.

3. Install 230 cm (90.6") of 5P743 Hose (13) on valve (12). Use a 5D1026 Clamp (17) to fasten thehose to the valve.

4. Route drain hose (13) to the rear access cover located in the rear bottom guard.

5. Remove two bolts from the transmission oil pan at the locations shown. Install 8J8197 Clip (14)with new 308535 Bolt (19). Install another 8J8197 Clip (14) with the bolt removed earlier.


6. Install 8J8197 Clip (14) and 7D7233 Clip (18) on drain hose (13). Fasten clips (14) and (18) to theexisting hole in the rear main frame crossmember with two 5P1075 Washers (16) and one S1594 Bolt(15).

7. Install the center bottom guards. Add oil to the transmission to replace that which was drained fromthe filter housing. Lower the cab.



Illustration 5. Location of drain lines for transmission oil filter housing on 973 Loaders.

Main Control Valve, Overspeed and Pilot Valve, Underspeed Valve

Service Tips

Make Sure All Parts Are Transferred From Used Transmission Control Valve To New ValveWhen A Replacement Is Made

When a used 3G4502 Valve Group is replaced by a new 3G4502 Valve Group, it is very importantthat ALL serviceable parts from the used valve be transferred to the new valve. There are two smallorifice plugs inside the 3G4502 Valve Group that are not part of the valve group. These two plugs arepart of the transmission control group. See the illustration. The illustrations and parts lists for thetransmission control group in the Parts Book should be used for reference when a replacement ismade.

If the 8J6815 Plug is not transferred from the used valve group to the new valve group, the machinebrakes will be released as soon as the engine is started. This could permit unexpected movement ofthe machine.



Location of 8J6815 and 9J8126 Plug in the 3G4502 Valve Group.

Wear In Underspeed Guide Assembly Can Cause Engine To Lug

Some machines may have a top speed that is as much as three seconds slow in 30 m (100 ft). Theremay also be problems in adjusting the full speed stops on these machines.

The cause of these problems is a notch worn in the 3G8475 Guide Assembly in the underspeed(actuator) valve group. This notch is in the guide assembly where the rollers ride during normaloperation.

Examine the 3G8475 Guide Assembly on the side nearest the spring. If it has a notch near the top ofthe oval slot, order a new guide assembly.

Underspeed valve group.



Loader Will Not Move; Plugged Orifice In Main Control Valve Can Be Backflushed

If the underspeed valve does not come up into position, the machine will not move. There can beseveral reasons for the underspeed valve not coming up into position. One reason is a plugged orificein the system going to the operate/brake valve spool.

It is possible to backflush the orifice (see the illustration) without disassembling the main controlvalve. First, use the procedure which follows to determine if a plugged orifice is the problem.

Procedure To Check For Plugged Orifice

NOTICE

The U-TUBE, if so equipped, must be in the test position or the hosefrom the transmission to the brake manifold must be plugged on later

machines.

1. With the centering bolt in the transmission lever, start the engine and bring it to high idle rpm. Pullthe transmission lever to BRAKES OFF position and check the pressures at plugs (1) and (2). SeeIllustration 1.

Illustration 1. Front view of transmission control valve.

NOTE: On later loaders and all loaders that have been reworked, the shunt line to the left charge andrelief valve will be connected at plug (1). Disconnect the line and remove the elbow to perform thesetests.

The pressure readings at both locations should be close to the charge pressure. If the pressure readingat plug (2) is close to charge pressure, a plugged orifice is NOT the problem. If the pressure reading atplug (2) is at or near zero and the pressure at plug (1) is close to charge pressure, then a pluggedorifice is possibly the problem. Go to Step 2.

2. Put the transmission lever in the PARK position. Remove plug (3) and start the engine. If oil flowsfreely out of the opening, it is an indication that plug (4) is missing. If oil does not flow out theopening, go to Step 3.



3. Make sure the linkage to the pilot valve is connected. If the pressure reading at plug (2) remains ator near zero, after the above procedure has been performed, the problem is probably a plugged orifice.See Illustration 2. Use the procedure which follows to backflush the orifice.

Illustration 2. Side view of transmission control valve.

Procedure For Backflushing An Orifice

1. Install a hose between the charge pressure tap (quick disconnect) and plug (2).

2. Pull the transmission lever into the full forward position. This will keep the starting vent stem in aposition that will allow the front side of the orifice to go directly to drain.

3. Start the engine and operate it at high idle rpm for a short period of time. Stop the engine.

4. Remove the back flushing hose and start the engine. Pull the transmission lever into the BRAKESOFF position. Check the pressures at plugs (1) and (2).

Valve Stem Behind Underspeed Cut-In Adjustment Plunger Will Not Move Freely

When adjusting the underspeed cut-in for hydrostatic transmissions, the light on the circuit tester mayremain on even through the adjustment plunger is backed out and the engine is at the proper cut-inadjustment speed. This can be caused by an incorrectly adjusted cut-in indicator tool or from the3G8706 or 4T2545 Stem not moving freely. The stem is located behind the underspeed cut-inadjustment plunger in the transmission control group. See the illustration.

The stem does not move correctly for one of two reasons: (1) the adjustment plunger is turned in sofar that the stem is forced into the bore, or (2) the hydraulic back pressure has been sufficient to forcethe stem into the bore. Either condition will cause the edge of the bore to deform, and the stem to beheld in place.

If this problem is encountered, inspect the stem to see if it moves freely.



1. Shut off the machine and remove the plug, lock, nut, plunger and seal as a unit. See the illustration.

2. If the stem is stuck in the bore, install a long screw with No. 8-32 threads in the tapped hole in thestem. Remove the stem.

3. Use a 9.35 ± 0.03 mm (.368 ± .001") diameter drill bit or reamer and a T-handle to clean up thebore. Apply a liberal amount of heavy grease to the flutes of the tool to hold the metal chips in theflutes. This will keep the chips out of the transmission.

4. Put a larger drill bit in the T-handle, coat the flutes with grease, and slightly chamfer the opening ofthe bore.

Illustration 1. Transmission control group.

5. Install the parts as shown in the illustration, and use the adjustment procedure shown in theappropriate Service Manual.

Illustration 2. View B-B of transmission control group.



Major Improvements

Installation Of Shunt Line And Removal Of Brake Check Valve Will Minimize Rollback

Some machines have had a problem with movement after the center brake pedal has been depressedor after the transmission control lever has been moved to the PARK position. Also, some machineshave experienced brief rollback motion just at the beginning of uphill movement.

The installation of a shunt line after the removal of the brake check orifice valve will stop movementof the loaders after the brake has been applied or after the transmission lever is put in the PARKposition. This will also minimize the rollback movement. This shunt line is factory installed on alllater machines.

See your Caterpillar Dealer for a list of the machines affected by this problem and for the new partsand installation procedure.

New Tube Used Between Underspeed And Overspeed Valves (943, 953, 963 Loaders)

A new tube and hardware are used in the hydrostatic power case lines groups on 943, 953 and 963Loaders. The new tube connects the underspeed and overspeed valves. The new tube has been used on973 Loaders since first production.

In some applications, the former tube has failed at the connectors that are on the ends. If the tube fails,it can slow or stop the machine.

See your Caterpillar dealer for a list of the machines affected by this change, a list of the new partsand the installation procedure.

Location of new tube in hydrostatic power case lines group.



Self-Locking Bolts Used In Underspeed Valve Group

DESCRIPTION OF CHANGE: Self-locking bolts are now used to hold the valve group to thebracket in the underspeed valve groups in the hydrostatic transmissions. The self-locking bolts havedeposits of nylon in the threads to keep the bolts tight.

ADAPTABLE AS: The new 6V9665 Bolts are direct replacements for the former 2B2694 Bolts inthis application. The new 6V9665 Bolts must be installed in place of the 2B2694 Bolts whenever theunderspeed valve group is disassembled. The new bolts are to be tightened to a torque of 25 ± 5 N·m(18 ± 4 lb ft).

Location of new bolts in underspeed valve group.

Drive System Does Not Operate Correctly; New Transmission Filter Relief Valve Spools

DESCRIPTION OF CHANGE: Three new filter relief valve spools are available for use in thetransmission control group. These valves are available in three different outside diameters. The newvalves have a hole in them which is perpendicular to their length. They are also longer to make betteralignment with bore in the valve group. These two changes will permit the valve to open more whenoil is sent to drain but still have enough length for good alignment in the bore.

The former valve spool was not available for parts service. With the former spool, it was possible fordebris to hold the valve in the "open" position. It was also possible for the spool, because of it'sshorter length, to get out of alignment with the bore. This caused the valve spool to stick (be held inplace). Either or both of these two problems can result in the type of operation which follows.

When transmission oil is cold, the relief valve is normally pushed open a small amount. In thisposition any foreign material on the pump side of the relief valve can be held in the narrow opening.



As the transmission oil becomes warm, the loader will only move slowly with the governor controllever at high idle. But when the governor control is moved forward, toward low idle, the loader movesfaster as the underspeed override valve is opened.

ADAPTABLE AS: The new valve spools are adaptable to 943, 953, 963 and 973 Loaders. The newvalve spools and their outside diameters are shown in the chart. The new spools can be installed asshown in the illustration.

When a loader has this operation problem, it is our recommendation that all three new valve spools beused to find out which one has the best fit with the bore in the valve group. The largest diameter spoolthat fits correctly into the bore must be used. This new spool can then be used as a direct replacementfor the former spool.

Location of valve spool in transmission control valve group.

Lock No Longer Used Under Nut On Adjustment Screw For Underspeed Cut-In

The 3S4506 Lock is no longer used under the nut on the adjustment screw for the underspeed cut-in.The lock was part of the transmission control group.

Because analysis has shown the lock is not necessary, the lock was removed to make assembly easier.Remove the 3S4506 Lock when the underspeed cut-in is adjusted.



Location of the 3S4506 Lock.

Standard Nut Used Instead Of Locknut To Hold Transmission Linkage Adjustment

DESCRIPTION OF CHANGE: A standard type nut is now used instead of a locknut on the pilotvalve rod end, and on the pilot valve linkage rod in the transmissions. Use of a standard nut in theseapplications makes assembly and adjustment of the linkage faster and easier.

ADAPTABLE AS: Direct replacement. The new 1B4201 Nut can be installed in place of the former2L9038 Locknut on all earlier machines, and the recommendation is to change the nut during anyservice work on these components. One nut is used on the 1U425 Rod End in the pilot valve group(overspeed), and one on the 3G8609 Rod in the hydrostatic power case linkage group.

Location of nut in pilot valve group.



Location of nut in linkage group.

Servo Control Valves And Linkage

Service Tips

Adjustment Of The Neutral Screws For Servo Valves In Hydrostatic Transmissions

Some servicemen have had problems trying to center the neutral screws for the servo valves in thehydrostatic transmissions. See the illustration.

A correctly adjusted neutral screw may not be centered when the servo valves are correctly adjusted.The Service Manuals say to "center the neutral screw" during assembly, this is not correct. Theneutral screw does not have to be centered.

The neutral screws can be adjusted either hydraulically or with the air neutral procedure given in theappropriate Service Manual. But, they must be adjusted after the centering spring, the direction-speedlink, the pilot valve link and the sync screws have been adjusted.

If desired, on machines with the shunt line installed, the following procedure can be used to makequick, approximate adjustments of the neutral screws. Then, make the final adjustment by using thepressure test procedure given in the Service Manual. Use the Service Manual as a reference during theprocedure.

1. Adjust the centering spring, the direction-speed link, the pilot valve link and the sync screws. Thisis done manually by inspection. See the illustration.

2. Close the synch shutoff valve.

3. With the transmission control lever held in PARK, start and run the engine at low idle.

4. Increase the engine speed in increments of 100 to 200 rpm as needed to hear the transmission noise.

5. Quickly adjust the neutral screws until the drive pressure decreases to zero and the transmissionnoise stops.

6. Continue increasing engine speed to high idle rpm.



7. Turn the neutral screw on each side clockwise until the noise is heard. Then, while counting theclicks, turn each neutral screw counterclockwise through the "no noise" range until noise is againheard. Turn the screws back clockwise one-half the counted number of clicks.

The neutral screws are now temporarily adjusted. Use the pressure test procedure, given in the ServiceManual, for the final adjustment.

Location of components under the top cover.

Correct Installation Of Oil Lines Between Servo Valves and Servo Cylinders

If a hydrostatic transmission was disassembled and assembled for repairs, and the transmission isexperiencing a high pressure on the left drive side that stops the engine shortly after it is started, it canbe assumed that the oil lines between the left hand servo valve and left hand servo cylinder were notinstalled correctly. Remember, these oil lines are crossed. The oil lines on the right side run parallel.See the illustration.

NOTE: Identification should be put on all lines before removing them. This will make sure that theyare installed in their original locations.

The engine will also be stopped or will stall to a lower speed if the neutral screws are out ofadjustment by a very large amount.

Correct location of oil lines between servo valves and servo cylinders.



Air Neutral And Pressure Neutral Adjustments Will Not Stabilize

If it is not possible to get a stabilized air neutral or pressure neutral adjustment when adjusting theneutral screw, there may be misalignment between the mechanical linkage plate and the servo valvebodies. This misalignment causes the servo valve sleeves to stick in the bodies. When installing servovalves, use the procedure which follows.

Installation Procedure

1. Put the servo valves in position in the case.

2. Install the bolts that hold the servo valves to the manifold. Do not tighten the bolts at this time.

3. Install the sleeves in the servo valves.

4. Put the power control unit linkage in position on the servo valves. Use care when the servo valvestems are installed into the servo valve sleeves. Make sure the plate of the power control unit linkagesets flat on the top of the servo valves. Move the power control unit linkage and servo valves a smallamount to put the servo valves, sleeves and stems all in alignment. Hand tighten the bolts.

5. Very carefully, remove the power control unit linkage from the servo valves. Tighten the two boltsthat hold each servo valve in place to 45 ± 3 N·m (33 ± 4 lb ft).

6. Install the power control unit linkage and make sure it installs freely over the top of the servovalves without any misalignment.

Machine Does Not Operate Correctly; Control Linkage Ball Can Come Loose From Stud

In some early machines, the rod ends in the internal hydrostatic transmission linkages were not stakedcorrectly. This can permit the control linkage ball to come loose from the stud. The result of this is themachine will stop or one steering pedal will not work correctly.

Your Caterpillar Dealer has a list of the machines affected by this and a procedure for correctlystaking the internal linkage rods.

Rod ends which were not staked correctly.

Axial Piston Pumps, Case, Pump Drive Housing

Service Tips



Failure Of Bearings And/Or Input Gears In Hydrostatic Transmissions 953 Loaders

Failures of the input gears and bearings in the hydrostatic power case groups and/or the rear bearingsin the axial piston pump groups, may be caused by too little or no lubrication. Oil normally flows tothe components through cross-drilled passages from core passages on each side of the transmission. Itis possible that the cross-drilled passages do not intersect the core passages on some 953 Loaders.This stops the flow of oil to the gears and bearings.

If burnt bearings and/or damaged input gears are found in a hydrostatic transmission, inspect the caseto make sure that the cross-drilled passages intersect with the core passages, and that the orifices inthe cross-drilled passages are open.

If they do not intersect, drill a 6.35 mm (.25") diameter hole between the drill passage and corepassage. Drill the opening at an angle behind the seal. See the illustration.

Location of oil passage in transmission case.

Oil Leakage Between Transmission Case Assembly And Pump Drive Housing At 5P4268 Seals963, 973 Loaders

The hydrostatic transmissions in some 963 and 973 Loaders have had oil leakage between the caseassembly and the pump drive housing. This leakage is caused by pressure surges in the transmissioncharging system. The surges become amplified at the end of the core passages in the main case andleakage occurs through the 5P4268 Seals. See Illustration 1. The leakage is usually seen on theexternal surface of the transmission, or there may be a change in the oil levels as the oil transfers fromthe main case assembly to the pump drive housing.



Illustration 1. Location of 5P4268 Seals in transmission case.

Whenever a hydrostatic transmission head is removed from an early 963 or 973 Loader or if thisproblem occurs, the oil supply from the core passage in the head assembly (both sides) to the deadend passage in the main case assembly should be plugged off. This will stop the leakage problem. Usethe procedure which follows to modify the head assembly.

Modification Procedure for Head Assembly

1. Remove the head assembly from the hydrostatic power case group.

NOTICE

Do not drop the port plates from their dowels on the head.



Illustration 2. Location of 9S8008 Plugs in head assembly.

2. Remove the 9S8008 Plug and the 3D2824 Seal from each end of the head assembly. SeeIllustration 2.

3. Drill a 6.2 mm (.244") diameter hole 15.0 mm (.59") deep in each side of the head assembly. SeeIllustration 3. Tap the holes with a 1/16"-27 NPTF tap. Thoroughly clean the head assembly at theselocations. Install the 2S7905 Plugs at these locations. Use 5P3413 Pipe Sealant with Teflon on thethreads of the plugs.

NOTE: Either 5P9452 or 304603 Plugs can be used as replacements for the 2S7905 Plugs.

4. Install the head assembly, the 3D2824 Seals and the 9S8008 Plugs. See the Service Manual forassembly and start-up procedures.

5. Check the oil levels in the hydrostatic power case group. Operate the machine and check for leaksor changes in the oil levels in the main case assembly and pump drive housing.

NOTICE

Do not plug this passage on 943 or 953 Loaders. This will result in animmediate failure of the piston pump bearing on the gear input end of

the pump shaft.



Illustration 3. View A-A.

Oil Transfer Out Of Hydrostatic Transmission

Oil can transfer out of the piston pump compartment in the hydrostatic transmission into: 1) theflywheel housing, 2) the pump drive portion of the hydrostatic transmission, or 3) into the drycompartment between the final drive and the main frame where the parking brake group is mounted.

If an oil transfer problem occurs in one of the three areas, the following checks should be made.

1. Oil transfer into the flywheel housing can be recognized by oil blowing out of the breatherlocated at the top of the flywheel housing. This can be confirmed by removing the 8B8817 Plugfrom the bottom of the flywheel housing. This is normally a dry housing. This type of transfercan be direct from the piston pump compartment through a cut 5H7153 Seal (used inhydrostatic drive group), indirectly through the pump drive or through the hydrostatic drivegroup into the flywheel housing.

When oil is observed blowing out of the flywheel housing breather, always check the oil levelsin the pump drive and engine to confirm the transfer of oil.

Use the procedure that follows to verify that the oil leakage is through the hydrostatic drivegroup and to correct the problem.

a. Remove the 8B8817 Plug from the flywheel housing, and check for clear transmission oil inthe housing. See Illustration 1. The housing normally is a dry compartment.

b. If transmission oil is found in the housing, refer to the Service Manual, and remove thehydrostatic drive group.



Illustration 1. Location of 8B8817 Plug in flywheel housing.

c. Inspect the hub assembly to see if the plate has moved from the press fit location. SeeIllustration 2. If the plate has moved, proceed to Step d. If the plate appears to be in place,remove the 7P7727 Shaft and stand the hub assembly with its plate end down. Pour some dieselfuel into the hub, and watch for leakage around the 8G2777 Plate. If leakage occurs, pour theremainder of the fuel out of the hub and remove the plate. Proceed to Step d. If no leakage isfound, check for transfer of oil through a cut seal or indirectly through the pump drive.

d. Using a dial indicator, check the roundness of the bore in the hub. If the bore is round within0.025 mm (.0010") or less, proceed to Step f. If the bore is out of round by more than 0.025 mm(.0010") proceed to Step e.

e. Machine the minimum amount of material necessary to make the bore round within 0.025mm (.0010").

f. Measure the inside diameter of the bore. Measure the outer diameter of the 8G2777 Plate. Ifthe bore measurement is more than 0.076 mm (.0030") larger than the diameter of the plate,proceed to Step g. If the plate diameter is within 0.076 mm (.0030") of the bore diameter,proceed to Step h.



Illustration 2. Location of 8G2777 Plate in the hub assembly.

g. Fabricate a new plate from low carbon steel to the dimensions given in Illustration 3. Thediameter of the plate must be 0.076 mm (.0030") larger than diameter of the bore. Proceed toStep i.

Illustration 3. Dimensions for new plate.

h. Using a knurling tool, knurl the outer edge of the 8G2777 Plate.

i. Thoroughly clean the plate and the bore in the hub. Put a liberal coating of 9S3265 RetainingCompound in the bore.

j. Install the plate in the hub assembly. Use a socket that is approximately the same diameter asthe plate to force the plate in place. Under no circumstances should the plate be forced in withonly a hammer.



k. Stand the hub assembly with its plate end down. Pour some diesel fuel into the hub, andwatch for leakage around the plate.

- If leakage occurs, repeat the procedure starting at Step d.- If no leakage occurs, install the shaft in the hub assembly.

l. Install the hydrostatic transmission.

m. Start and operate the machine.

2. Oil transfer into the pump drive housing can be recognized by a greatly elevated oil level atthat location and a lowering of the oil level in the sight gauge of the piston pump compartment.This is generally caused by one of the three 6V3382 Seals (used in the hydrostatic power casegroup) being installed at a slight angle or the sealing lip of the seal is cut. It is also possible thata 5P7031 Seal may have been installed in place of a 6V3382 Seal on the inner end of the9J3061 Gear.

NOTICE

When 6V3382 Seals are installed, use a flat plate with a hole which willfit over the pump shafts. This will make sure that the seals are installedsquare with the housing. If a new seal lip running surface is needed, aninstallation washer no thicker than 1.600 mm (.0625") can be used toreposition the seal shell below the machined surface of the housing. Aseal which is installed out of square by 0.51 mm (.020") or more, will

allow oil to be pumped under its sealing lip during normal shaftrotation.

3. Oil transfer into the dry compartment between the final drive and main frame can berecognized by a loss of oil from the piston pump compartment with no increase in oil level inany other compartment. This is caused by loose fittings in the parking brake lines group. Thefinal drives must be removed to make this repair.

Use the information which follows to check the dry compartment in the main frame.

943 and 953 Loaders: Loosen the 8G930 Spanner Nut in the parking brake group. If oil drains out, itcan be assumed an internal oil leak exists.

963 and 973 Loaders: Remove the bolt from the main frame at the location shown in Illustration 4 orIllustration 5. If oil drains out of this location, it can be assumed an internal oil leak exists.



Illustration 4. Main frame for 963 Loaders.

Illustration 5. Main frame for 973 Loaders.

Major Improvements

Seal Added To Hub Assembly In Hydrostatic Drive Groups (963, 973 Loaders)

DESCRIPTION OF CHANGE: A seal has been added to the hydrostatic drive group for 963 and973 Loaders. The new seal fits between the existing seal of the same part number and the splines onthe hub assembly. See the illustration. The extra seal will decrease oil leakage through the gear borethat is possible because of component tolerances.

ADAPTABLE TO: The 5H7153 Seal can be added to all earlier 963 and 973 Loaders as shown inthe illustration.



Locations of the new and existing 5H7153 Seals in the hydrostatic drive groups.

New Liquid Sealant Used Between Pump Drive And Hydrostatic Case Housings

DESCRIPTION OF CHANGE: A new sealant is used between the pump drive housing and thehydrostatic case housing. The new sealant will remain a liquid until the pump drive housing and thehydrostatic case housing are connected, and the bolts are tightened. Extra sealant will dissolve in oil.The sealant can be removed easily with a putty knife or scrub pad during later disassembly work. Newsealant can then be used during assembly.

ADAPTABLE AS: The new 6V6640 Sealant is a direct replacement for the former 7M7260 Sealantused at this joint. Apply the sealant to only one of the faces that are connected.

NOTE: The surfaces that are to be sealed must be slightly rough to retain the sealant when the pumpdrive housing is bolted to the case housing. The finish on the surfaces should be approximately 2.9 to3.8 micrometers (116 to 152 microinches). If the surfaces are too smooth they can be made rougherwith a fine file. Do not use a caustic or phosphate cleaning solution on the surfaces.

New Axial Piston Pump Groups Have Better Lubrication Between Piston Assemblies AndBarrel Assembly (953, 963, And 973 Loaders)

DESCRIPTION OF CHANGE: New axial piston pumps groups are used in 953, 963 and 973Loader transmissions. These new pump groups have new piston assemblies with a smaller diameter.This smaller diameter gives better lubrication between the piston assemblies and the barrel assembly.

ADAPTABLE AS: The new pump groups are direct replacements for the former pump groups asshown in the chart. The new piston assemblies can be used with the former piston assemblies in thesame pump group.



Rotate Input Shafts During Installation Of Pump Head On Hydrostatic Transmissions

During installation of the pump head on the hydrostatic transmission case, it is very important torotate (turn) the pump input shafts as the head bolts are tightened. The pump input shafts, bearings,and barrels can drop out of alignment a small amount when the head is removed.

During installation of the head, rotation of the input shafts will bring the bearings into correctalignment in the head. Damage to internal components is possible if this procedure is not followed. Ifthe head on the hydrostatic transmission has been assembled correctly, the serviceman will be able toturn the main input shaft with a 61 cm (2 ft) extension bar or pipe wrench.

New Spring Used In Axial Piston Pumps 943 Loaders

DESCRIPTION OF CHANGE: A new spring is used in the axial piston pump on 943 Loaders. Thenew spring is longer and will permit pump assembly with only two spacers. The former spring neededthree spacers to get the correct assembled load.

ADAPTABLE AS: The new 4T360 Spring and two 8J482 Spacers are a direct replacement for theformer 3G6488 Spring and three 8J482 Spacers. The new spring has a yellow stripe and is 91.95 mm(3.580") long.

Three spacers must still be used in pumps that have the former spring.

Location of the spring and spacers.

Charge And Main Relief Valve, Sync Valve, Oil Cooler



Service Tips

Overheating Of The Hydrostatic Transmission

Anytime overheating of the hydrostatic transmission occurs, check the transmission oil cooler core forexternal restrictions or plugging. To do this, move a shop light to all areas behind the core and inspectaround the tubes for restricted and plugged areas. The area around the tubes may not be totallyplugged, but enough debris may be wrapped around the tubes to provide sufficient restriction to causeoverheating.

If restricted or plugged areas are found, clean the core with high pressure steam and soap. Highpressure water or air alone will not clean the core, steam and soap must be used. The fin spacing andtube spacing are closer on transmission cooler cores than on engine radiators. For this reason, morecareful methods of cleaning are required on transmission cooler cores.

NOTE: On 953, 963 and 973 Loaders, the hydraulic oil cooler must be folded down to allowcomplete cleaning of the transmission cooler core. In some cases it may be necessary to remove theoil cooler and have the cooler cleaned at a repair shop.

Use Only Forged 307948 Elbows In Line Between Sync Valve And Sync Shut-Off Valve

The 307948 Elbows were originally made either as a fabrication (and the parts brazed together) or asa forging. The fabricated elbows can be identified by their gold color. The forged elbows can beidentified by their silver color. Now, only forged elbows are made.

The brazed (gold colored) 307948 Elbows have separated in some hydrostatic transmissionapplications. Because of this, use only the forged (silver colored) 307948 Elbows in the hydrostaticpower case lines group. Any brazed elbows should be used in other applications.

Quick Response And Filter Relief Valves Can Be Easily Removed For Service

The Disassembly And Assembly Sections of the Service Manuals for these loaders, show how toremove the main control valve. In the disassembly of the main control valve they show how toremove the quick response and filter relief valves from the control valve. The Service Manuals showthe removal of the control valve and its manifold as a unit. If service work is to be done on only thequick response or filter relief valves, the manifold does not have to be removed. This will make itpossible to leave the top cover of the power control unit and the pilot valve in position and eliminatethe need to readjust the top linkage after the control valve is installed. To remove the main controlvalve and still leave the manifold in position, use the following procedure:

1. Remove the oil filter housing.

2. Remove the oil lines shown in the illustration and disconnect the oil lines on the other side of thecontrol valve (not shown).

3. Fasten a hoist to the control valve.

4. Remove the five bolts on the side of the main control valve that hold the valve to the manifold andpower control unit. (On some models it may be necessary to remove the charge pump.)

5. Remove the seven bolts that hold the control valve to the manifold.



6. Remove the control valve.

Location of the parts that must be removed.

Major Improvements

New Spacer Used In Assembly Of Screens On Oil Cooler Return Tube In Transmissions 943,953, 963 Loaders

DESCRIPTION OF CHANGE: A new spacer is used on the bolt that holds the three screens on theoil cooler return tube in the hydrostatic power case lines groups. The design of the new spacer permitsbetter control of tolerances, especially spacer length. This will make sure the screens are held in placewith the correct amount of force when the bolt is tightened. Formerly, it was possible for differencesin spacer length to cause either too much or too little force to hold the screens correctly in place.

ADAPTABLE AS: The new 4T5919 Spacer is a direct replacement for the former 3H3244 Spacer,and can be installed in the hydrostatic power case lines groups on all earlier 943, 953 and 963Loaders.

Plugs Removed From Charge And Main Relief Valves For Hydrostatic Transmissions

DESCRIPTION OF CHANGE: A change has been made to the charge and main relief valves inhydrostatic transmissions. The valve bodies used in these valve groups have been changed to removeseveral holes which are not needed, and the plugs and seals for these holes are now removed from thevalve groups as shown in the illustrations. This will prevent the possible development of leaks aroundthe plugs. The holes in which the plugs were installed were used for special tests, and are notnecessary for normal tests or for troubleshooting.

ADAPTABLE AS: Direct replacement. The part numbers of the 3G5008 (RH), 9J365 (LH), and9J8554 (RH) Valve Groups are not changed. Three 9S4191 Plugs and three 3J1907 Seals are removedfrom the 3G5008 Group, and four 9S4191 Plugs and four 3J1907 Seals are removed from the 9J365and 9J8554 Groups. The illustrations show the locations of the plugs and seals in earlier valve groups.Later groups have no holes for these parts.



Locations of plugs and seals in earlier 3G5008 Valve Groups (RH).

Locations of plugs and seals in earlier 9J8554 Valve Groups (RH). The 9J365 Valve Groups (LH) use the same basic

valve group and valve body, so hole locations are the same for both groups.

Hardened Washers And New Bolts Used To Prevent Loss Of Bolt Torque

DESCRIPTION OF CHANGE: Hardened washers and new bolts are used in the hydrostatic powercase group to hold the charge and main relief valve groups in place, on the above machines. With thewasher, the force caused by the torque on the bolts pushes against a larger surface area and will holdthat torque better.

Formerly, washers were not used under the bolt heads. It was possible for the bolt heads to causedistortion of the valve body during high pressure conditions. The result of this was a possible loss ofbolt torque and leakage past the seals between the valves and the hydrostatic transmission head.



Because of the thickness of the washers it was necessary to use longer bolts in some of the locations.The new bolts are 6.35 mm (.25") longer than the original bolts.

ADAPTABLE TO: The washers and new bolts are adaptable to all 943, 953, 963 and 973 Loaders.The torque specification for these bolts did not change.

Location of bolts and washers.

Teflon Ring in Transmission Charge and Main Relief Valve Groups Can Be Cut For EasierInstallation

There have been changes made to some components in the charge and main relief valve groups in thehydrostatic transmissions. The 9J8136 Seats were replaced by the 1U4833 Seats and the 306121Rings were replaced with 300167 Rings in the sync valve. See the illustration. The new 300167 Ringcan be either a split Teflon ring or a solid one. Installation of the solid ring can be difficult. The ringmust be stretched and twisted during installation. This can damage the ring. Our recommendation is touse a sharp knife and cut the solid Teflon ring at 45° to 60° angle for easier installation. Nomodification is necessary if the 300167 Ring is already split.



Location of Teflon rings in sync valves.

Brakes And Motors

Service Tips

Use A Brake Release Pump When Towing Track-Type Loaders

The brakes must be released when hydrostatic loaders are towed. Former loaders had an on-boardhand pump which released the machine brakes. New loaders need an external (outside) power source.

You can fabricate a portable pump group that is hand powered. The FT1845 Pump Group has a7H1680 Volume Compressor (Pump) with a gauge, hoses, valves, and fittings. These components arenecessary to control the oil pressure and connect the pump to the brake circuit.

Follow this procedure to make the pump group:

1. Remove the original hose and fittings from the pump.

2. Use the instructions printed on the side of the pump reservoir to adjust the pump handle linkage to17 000 kPa (2500 psi) position (maximum volume per stroke).



Illustration 1. FT1845 Pump Group.

3. Add the hose and fittings to the pump cover. See Illustration 1 for correct assembly and partsidentification.

4. Fill the reservoir with SAE 10W oil.



5. Before you use the pump group to release the loader brakes, adjust the 8T477 Relief Valve on thepump group:

a. Close the manual valve (Item 3 in Illustration 1) and plug the end of the hose with a 5P2909Plug.

NOTE: Install a 26453 Elbow (1/2" - 14 NPT street elbow) in the relief valve port on the sideof the 8T477 Relief Valve. This street elbow is not part of the FT1845 Brake Release Group.Make sure the elbow is directed toward the pump reservoir. Remove the cover of the pump toallow oil flow from the relief valve port to fall into the pump reservoir while the relief valve isset.

b. Adjust the relief valve so it starts to drip oil at approximately 1380 kPa (200 psi) whileslowly pumping.

c. The pressure reading at the gauge will increase as you pump faster to increase the rate of oilflow through the relief valve. While you operate the pump handle at the rate of one stroke persecond, adjust the relief valve again, if necessary, so the maximum pressure reading is between1900 kPa (275 psi) and 2075 kPa (300 psi) with all the pumped oil flowing through the reliefvalve. This will protect the tractor brakes from excessive pressure surges.

d. After adjusting the relief valve, open the manual valve to return the pressure to zero. Removethe 5P2909 Plug from the hose. Install the cover on the pump reservoir.

6. You must connect the service pump hose to the 8M505 Fitting at the inboard side of the3W305 Manifold. The manifold is at the rear of the left ROPS support.

a. Disconnect the hose which comes from the transmission and plug it with the 5P2909 Plug.See Illustration 2.

b. Connect the service pump hose to the 8M505 Fitting. This is the fitting from which the hosewas removed.

7. Block the machine to prevent movement.

When the brakes are released, the machine is free to move. This couldcause personal injury or property damage. Block the machine to

prevent movement until it is ready to tow.



Illustration 2. Pump connection to manifold.

8. Close the manual valve. Pump the oil until it reaches a pressure of 1025 to 1375 kPa (150 to200 psi). This will fully release the brakes. You can maintain this pressure by an occasionalstroke on the pump handle on a brake system that is in good working condition. The pressuremust not reach more than 2075 kPa (300 psi).

NOTICE

Brakes must be fully disengaged when the loader is towed. If they arepartially engaged, they will overheat and damage will result. Keep the

pressure between 1025 and 1375 kPa (150 and 200 psi) to be surebrakes stay disengaged. Pressures that go higher than 2075 kPa (300

psi) can damage the components of the brake system.

Personnel operating the service tool while riding on the towed machineshould keep the seat belt fastened to prevent possible injury when the

machine suddenly stops.

9. If the brakes must be used, turn the valve (Item 3 in Illustration 1) 90° to the open position.The pressure of the circuit will drop to zero and the brakes will work immediately. The machinewill stop suddenly.

10. To apply the brakes after the machine is towed, turn the manual valve handle 90° to theopen position.



False Leakage Indications Possible During Instrument Tests On HydrostaticTransmissions

False indications of excessive (too much) leakage are possible during instrument tests on thehydrostatic transmissions used in some track-type loaders.

The Service Manual instructions for the "Instrument Tests" tell you to "change the location ofthe U-TUBE on the brake instruction panel from RUN to TEST," during preparation of themachine. See the illustration.

When the U-TUBE is in the TEST position, oil under pressure from the transmission is sent tothe hand pump. If there is leakage past the check valves in the hand pump, the oil will flow intothe sump of the transmission. This leakage into the sump will cause a) low charge pressureindications and/or b) low cooler flow indications during the instrument tests.

If low charge pressure indications and/or low cooler flow indications are present, move the U-TUBE to the TOW position and install the cap tightly on the open port. Do the instrument testagain to find if the leakage is in the hydrostatic transmission or in the hand pump. If the leakagewas in the hand pump, the charge pressure and cooler flow indications will now be normal.

Location of the U-TUBE and the brake instruction panel.

Major Improvements

Plunger Assembly Replaces Adjustment Screw In The Speed Override And BrakeControl Pedal

The 3W3321 Plunger Assembly replaces the 4B3615 Adjustment Screw. The 1D5117 Nut isstill used with the new plunger assembly. This plunger assembly does not affect the operationof the speed override and brake control pedal. When the pedal is pushed down until the springin the plunger assembly is felt, the transmission pumps will be close to zero angle and the



brakes will still be released. When the pedal is pushed past the spring to the stop, the brakeswill be applied. The 3W3321 Plunger Assembly is in effect as shown in the chart.

Adjustment Procedure For Plunger Assembly

1. Turn the plunger assembly until it is even (flush) with the bottom of the pedal.

2. Use the procedures given in the appropriate Service Manual to adjust the speed override andbrake control group.

3. For adjustment of the plunger assembly, hold the pedal down until the lever makes contactwith the stop on the brake valve housing. With the pedal in this position, turn the plungerassembly in until the plunger contacts the pedal support housing.

4. Release the pedal.

5. Turn the plunger assembly clockwise, four additional turns. Tighten the 1D5117 Nut to 45 ±7 N·m (33 ± 5 lb ft).

Location of speed override and brake control components.

To check the adjustment of the plunger assembly, install a pressure gauge in the brake pressuretap on the top of the transmission control valve. Start the engine and bring it to high idle rpm.Put the transmission control lever in the BRAKES OFF position. The brake pressure will showon the gauge. Push the center pedal down until the plunger just makes contact with the pedalsupport. The gauge reading should remain the same. Push the pedal all the way down and thepressure should go to zero.

New Joint Assembly Used In Piston Motor 943 And 953 Loaders

DESCRIPTION OF CHANGE: A new joint assembly is used in the piston motor group on943 and 953 Loaders. The new joint assembly is stronger and will have a longer service life.



ADAPTABLE AS: The new 4T8689 Joint Assembly is a direct replacement for the former4T1693 Joint Assembly which is canceled.

Use Thread Sealant To Prevent Oil Leakage Around Stop Bolts In Track Motor Groups973 Loaders

Location of 3G9710 Bolt in 3G5014 Track Motor Group.

There have been reports of oil leakage around the 3G9710 Stop Bolts in the 3G5014 TrackMotor Group on 973 Loaders. See the illustration. The leakage can be prevented with threadsealant. If a machine has this problem, make an alignment mark on the head of the bolt and onthe case. Count the number of turns needed to remove the bolt. Put 7M7260 Liquid Gasket onthe bolt. Install the bolt back into the motor group case with the same number of turns. The boltwill then be in its original position.

NOTE: If bolt is not returned to its original position, the motor angle will be changed and cancause machine to drift right or left during operation.

If the track motor group is disassembled for any reason, be sure to put liquid gasket on thethreads of the stop bolts.

New Shaft And Retainer Available For Field Installation In Piston Motors 943, 953, 963Loaders

DESCRIPTION OF CHANGE: A new shaft and retainer, with a different snap ring and a pin,are available for field installation in piston type hydraulic motors used on the above models.The new parts are used for replacement of the former retainer and snap ring to hold the barrelspring in existing hydraulic motors, and have a new stronger design for longer service life. Onsome machines, failure of the former snap ring and/or retainer has caused too much case drainleakage and loss of torque from the motor.



ADAPTABLE TO: The new parts shown in Chart A can be installed in the piston motorgroups shown in Chart B on existing machines. This conversion permits removal of the former9J8052 Retainer and 8J6274 Snap Ring. The new parts must be used together for conversion ofeach motor.

New Universal Joint Used In Piston Motor Group 963 And 973 Loaders

DESCRIPTION OF CHANGE: A new universal joint assembly is used in the piston motorgroup on 963 and 973 Loaders. The new universal joint assembly has a stronger input yoke.The new yoke will give a longer service life.

ADAPTABLE TO: The new 4T7480 Universal Joint Assembly is a direct replacement for theformer 4T905 Universal Joint Assembly. See the illustration for the location of the newuniversal joint assembly.

Location of universal joint assembly in piston motor group.



New Sleeve In Hydrostatic Piston Link Motor Group Has More Resistance To Wear 973Loaders

DESCRIPTION OF CHANGE: A new sleeve is now used in the hydrostatic piston motorgroup on 973 Loaders. The new sleeve is made of a harder bronze material. Because of the newmaterial, the new sleeve has more resistance to wear.

ADAPTABLE AS: The new 4T2060 Sleeve is a direct replacement for the former 3G9706Sleeve, which is canceled.

Location of 4T2060 Sleeve in the motor group.

General

Service Tips

Checking Right Drive Pressure On Hydrostatic Transmissions 973 Loaders

Reports have been received concerning the difficulty in checking the right drive pressure onhydrostatic transmissions in 973 Loaders.

When servicemen attempt to use a 6V4144 Coupling with the high pressure test hose, they findthe fitting cannot be installed on quick disconnect couplings on the hydrostatic transmission.The coupling to adapter to elbow combination is too long and, thus, interferes with the tank.

When checking the right drive pressure, use a 6V4143 Coupler connected directly to a 3B6552Elbow. The elbow, in turn, is connected directly to the high pressure test hose. These parts canbe easily installed on the quick disconnect coupling on the sync valve to read right drivepressure.

Procedure To Tilt Operator Platform On Machines Without A Cab

Some dealers have desired information about the correct procedure to use when the operatorplatform must be tilted forward on loaders which are not equipped with a cab. Because of the



different weight balance without a cab, the platform on these machines can not be tilted a full90° with a single hoist. Use the procedure that follows:

1. Use the shop hoist to tilt the platform as far as possible.

2. Fasten a 5P9694 Ratchet Hoist between the lift hole on the back of the bucket, and the rear ofthe platform at the location of the opening for the instrument panel.

3. Use the ratchet hoist to pull the platform forward until the 8G148 Safety Brace Group can beinstalled.

4. To lower the platform, use the reverse procedure.

Do not use the 5P9694 Ratchet Hoist to lower the platform beyond theposition where it was lifted by the shop hoist. Use the shop hoist to lower

the platform beyond this position.

Case Drain Pressure Measurements

When troubleshooting hydrostatic transmission problems, be sure to look at the test gaugescarefully when starting the machine. If there is a total failure in one of the motors, the pressurecould "peg" the gauge needle (move the gauge needle around to the stop) when the engine isstarted. The serviceman that is troubleshooting the transmission might read the gauge pressureas zero pressure. This will make troubleshooting difficult and will increase the time needed tomake repairs.

Correct Assembly Of Connectors In Hydrostatic Transmission

There have been problems of separation of some tubes and connector assemblies in thehydrostatic transmission for 943 and 953 Loaders. This separation will give a loss in oil flow.Wrong assembly of the connector assembly can cause this separation.

The parts of the connector assembly must be assembled in exactly the same position andsequence as shown in the illustration. For example, the anchor, which is similar to a bevelwasher, must be installed with the small diameter toward the end of tube as shown. If theanchor is installed in the wrong position it can permit a separation of the tube from theconnector assembly.



Correct position of connector assembly parts.

Major Improvements

New Nut Assembly For Fittings In Hydrostatic Transmission

A new 5P8752 Nut Assembly is now available for parts service. This new nut assembly is usedon several different fittings in the hydrostatic transmission. The nut assembly permits thereplacement of the nut, retainer, anchor, guide and seal in these fittings. Before, the completefitting had to be ordered if one of these components was damaged.

The 5P8752 Nut Assembly can be used for service of the 5P8547 Tee, 5P8548 Connector,5P8549 Connector or 5P9036 Elbow.

Nut Assembly Now Available For Parts Service

DESCRIPTION OF CHANGE: The nut assembly that is used on the 5P8750 Connector andthe 5P8546 Elbow in the hydrostatic power case lines group is now available for parts service.

Formerly, this nut assembly was not available for parts service. If the nut assembly wasdamaged, it was necessary to make a replacement of the complete connector or elbow.

ADAPTABLE AS: The new 5P8751 Nut Assembly is adaptable to all 5P8750 Connectors and5P8546 Elbows.



Position of nut assembly on connector and elbow.

Longer Stud Used In Governor Control Groups 963, 973 Loaders

DESCRIPTION OF CHANGE: A new stud is used in the governor control groups on 963 and973 Loaders. The new stud is longer than the former control rod. Because the stud is longer,more threads in the rod ends are engaged with the studs. Formerly, if both locknuts becameloose, it was possible for the control rod to turn and then become disconnected from the rod endand lever on the transmission. This caused the underspeed override valve to open. When a loadwas put on the engine, the open valve would cause the engine to stall. Also, because not enoughthreads were engaged in the rod ends, an incorrect governor control linkage adjustment waspossible.

ADAPTABLE AS: The new 2K2773 Stud is a direct replacement for the former 2M2830 Rod.



Location of new control rod.


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