Automatic Drive P.O. Box 440Bellows Falls, VT 05101-0440 USA800-843-2600 • fax: 802-463-4059

email: info@sonnax.com •www.sonnax.com

©2008 Sonnax Industries, Inc.

Some things are less intimidating if you’re notthe first to do it. That statement applies both tocrossing a frozen lake and working on a prob-lematic AW55 50SN. On the lake, heavy snowcover can prevent you from telling if the ice issufficient for support, and what you can’t seemay end in a sink-or-swim experience. On the55 50SN valve body, a clean core does not meanthe valve body is functioning correctly.

This material is a route that other travelers havemarked past the “thin ice” of the AW family. Atthese flags, the test or inspection frequentlypoints to a problem in the valve body, as thisaccounts for the majority of the transmission’sissues. The 55 50/51 SN is installed in a multi-tude of vehicles, and there will be variations tothe unit and this data. A similar valve body willbolt to a GM, Volvo, Saturn, Nissan, Saab, Opelor Renault. Failure to test and recognize the dif-ferences among them can create hours of addi-tional effort.

Pressure and fillAll the pressure plugs have a 12mm head. Donot mistake the 27mm band anchor (see Figures1 and 2) for a fill plug or pressure tap. If thatanchor is removed, the band will have to berecaptured. Positioning the band requiresremoval of the servo at best, and possibly thecomplete transmission.

The turbine/input sensor hole can be used toimprove the fill speed. Low fluid or excessiveoverfill can create erratic pressure and poor lin-

ear solenoid control, eventually forcing a TCMhigh pressure strategy.

If the transmission is in the vehicle, “test the ice”at the pressure taps relative to these complaints:

• TCC RPM fluctuation and overheated fluid Check lube pressure. The lube pressure tap isbetween the secondary regulator valve and themain shaft bushings. Lube pressure will beaffected by the fluid viscosity (flow rate) and thebushing-to-shaft clearance. Sufficient pressureat operating temperature indicates the filter,pump and both primary and secondary regula-tors are functioning. Normal lube pressure atthe port indicated: At -10º Fahrenheit, lubepressure can be as high as 30 psi. At 150ºFahrenheit, normal lube will be 5 psi in driveand 8 psi in reverse. This indicates the bushingsare in place and can retain some of the sourcepressure. Lube pressure that starts low and staysat zero psi indicates your pump output is low,the regulator valve bore is worn or your bush-ings are bad.

If you are diagnosing a TCC complaint, per-form a cooler flow test. Normal flow in drivewith TCC released is 1.3 gpm and during TCCapply it drops to .7 gpm. The Saab cooler ele-ment will require an adapter, but most units areeasily accessible.

Lube pressure and flow on the 55 50SN is lowin comparison to other units. This converter

Adapting to the AW55-50SN valve bodyArticle No.:

Author:

Total Pages:

TASC Tip-02-08

Bob Warnke

3

Mainshaft lube

C-1

B-5

SLT

C-3 C-1

C-3

Figure 1

Figure 2

continued on page 2

Input speed sensor

27mm band anchor

B-4 servoB-4 tap

Output speed sensor

requires multiple valves,along with the rear pumpbushing to control modulat-ed TCC apply (see Figure3). The converter clutchmay remain fully applied atvery low speed and highload, which taxes the fluidand lining, creating a break-away slip or RPM fluctua-tion.

• Delayed engagements andpoor/flare shiftsCheck SLT pressure and theC-1 clutch. The C-1 clutchis engaged via pressure riseby the SLT solenoid andthrough a series of modulat-ed valves. The SLT pressureshould start at 5 psi in driveand increase with throttleand load to 80 psi maxi-mum. SLT will cut back andspike on various shifts,depending on the TCM program.

Typical C-1 pressure is zero in park. As drive is selected, it quickly stepsto 25 psi, then 50 psi, within a half-second and remains until accelerated.C-1 psi will then follow load, with a maximum near 200 psi. If C-1 pres-sure upon selecting drive is immediately 160 psi and achieves 200 psi dur-ing a shift, the unit may be under a TCM code/ failsafe mode.Engagements at this time are abrupt. Some vehicles (Volvo, specifically)may use a C-1 disengagement via brake signal creating a neutral at idle.Check for a TCM flash to eliminate this condition.

• 2-3 shift flare, neutral or harshCompare the B-4 servo apply pressure to the C-1 clutch. The B-4 tap isat the top of the case, in line with the linkage bolts. The B-4 circuit hasextensive valve body control and includes a tube with o-ring ends thatfeed the servo. Comparing C-1 to B-4 is an indication of control by theSLS and SLT linear solenoids, a failsafe or leakage condition.

Proper B-4 pressure should follow C-1 and never be less than 10 psi of C-1 (refer to the C-1 pressure testing). If C-1 psi is fixed at 160 psi onengagement, the 1-2 and 3-4 shift may be acceptable, but the 2-3 is gen-erally too harsh. A TCM pressure management code, aerated fluid or abad speed sensor will eliminate the SLT pressure curve and force B-4 toan immediate 200 psi, which results in the harsh 2-3 shift. If the pressurecurve of both C-1 and B-4 are parallel, C-1 initial engagement is near 50psi and the 2-3 is harsh, the vehicle may require a flash update, but per-form a key cycle and numerous drive cycles first. Some manufacturers

(Volvo) have servos and a reflash to improve 2-3, 3-2 drivability.

• SLT air testBefore removing the valve body from the transmission, you can performa visual Wet Air Test of the SLT circuit. If you pressurize the SLT portwith shop air (80-100 psi), air pressure will push fluid, which you see asa leak. Problematic leaks occur at the steel side cover, SLT accumulator,

B-1 and C-1 control valves. A major leak – or combination of leaks – cancause delayed engagements or flare upshift and should be inspected afterdisassembled.

You can perform a similar air test with the valve body itself (see Figure4). When doing so, the pump line port and thermal element hole mustbe closed and the separator plate held as shown to eliminate cross leaks.This might sound confusing in print, but when you do it, the ports willbe evident and easy to close with your other hand.

Valve body inspectionThere are many variations, which complicates coring and matching parts.Figure 5 identifies visual changes. Currently there are six different shiftsolenoids, four of which can be installed in the wrong locations orreplaced by a normally open vs. normally closed solenoid. The shift sole-noids should be checked for proper flow when open and for sealing whenclosed. These are fed line pressure from an orifice in the plate, and can beover-pressurized.

Three linear solenoids are calibrated to the valve body. Exchanging SLTand SLS solenoids between cores without adjusting to the valves is gener-ally not acceptable. Don’t hesitate to open and inspect the valve body

Article No.: TASC TIP-02-08 Author: Bob Warnke ©Sonnax Industries Inc. Page 2

Converter release oil

Lube oil

Critical pump stator bushing

Lockup control bore

SLT test location

Air test plate

SLT accumulator bore

Output gear lube seal

Line port

B-3 seal

continued on page 3

Figure 3

Figure 4

since it’s comparable to other Aisin Warner designs and is not difficult toreassemble. That inspection should include all the removable sleeves, bothregulator valves and the solenoid modulator bore. The linear solenoids arefed by this modulator valve, which limits the maximum pressure. Whenthat bore is worn, the concern is similar to a bad GM actuator feed circuit.

Excess wear appears as a discoloration, or polished area, in the shape of amoon phase, generally at the ends of the bore or opposite side of fluidentry (see Figure 6).

Bob Warnke is vice president of technical development and a member of theTASC Force (Technical Automotive Specialties Committee), a group of recog-nized industry technical specialists, transmission rebuilders and SonnaxIndustries Inc. technicians.

©2008 Sonnax

Article No.: TASC TIP-02-08 Author: Bob Warnke ©Sonnax Industries Inc. Page 3

Figure 5

Cast numberPlate code

Vented/no ventSLT

SLS

SLU

Thermal sensor

Up or downposition

Insulator color varies9165 = early

No code = earliestC Code = latest

N.OorN.C

#1

#2#4

#5#3

Note shadows from excess bore wear

Figure 6