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Drum Brake OverhaulDrum Brake Overhaul

Roger BortignonRoger Bortignon

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• hubless drums slide right offhubless drums slide right off often they may have to be often they may have to be

tapped with a hammer to free tapped with a hammer to free them upthem up

• some imports have 2 threaded some imports have 2 threaded

holes holes install two 8mm bolts to pull install two 8mm bolts to pull

the drum offthe drum off

• drums with integral hubsdrums with integral hubs remove dust capremove dust cap unlock retaining nutunlock retaining nut remove washer & bearing remove washer & bearing

Drum RemovalDrum Removal

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Drum Brake Replacement & OverhaulDrum Brake Replacement & Overhaul• items that will need inspection, service or replacement include…items that will need inspection, service or replacement include…

Friction partsFriction parts brake shoesbrake shoes brake drumbrake drum

Hydraulic partsHydraulic parts wheel cylinder & brake fluidwheel cylinder & brake fluid

HardwareHardware emergency brake cablesemergency brake cables brake return springsbrake return springs

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• this is NOT a step-by-step procedurethis is NOT a step-by-step procedure

• every vehicle is slightly differentevery vehicle is slightly different

• experience & personal preference dictates the order for re & reexperience & personal preference dictates the order for re & re

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Brake Shoe RemovalBrake Shoe Removal

• clean brake assembly by wet washing – use a dust maskclean brake assembly by wet washing – use a dust mask use brake washer – if on the hoistuse brake washer – if on the hoist or use spray bottle with soapy solution set to mist or use spray bottle with soapy solution set to mist do NOT use compressed air on dry brake assemblydo NOT use compressed air on dry brake assembly!!

• remove upper return springsremove upper return springs

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Brake Shoe Removal – Special ToolsBrake Shoe Removal – Special Tools

• use brake spring pliers, not screwdrivers or general purpose use brake spring pliers, not screwdrivers or general purpose pliers – easier, safer & quickerpliers – easier, safer & quicker

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Brake Shoe RemovalBrake Shoe Removal• remove hold down springs (may require special tool – fig.a)remove hold down springs (may require special tool – fig.a)• unhook e-brake cable (see next slide)unhook e-brake cable (see next slide)• remove shoesremove shoes

fig. a

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Emergency Brake Cable RemovalEmergency Brake Cable Removal

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Wheel Cylinders – what should I do with it?Wheel Cylinders – what should I do with it?

• has the brake fluid been flushed out every 2 years?has the brake fluid been flushed out every 2 years?• is it leaking? is it leaking? • how old is the vehicle?how old is the vehicle?• should I leave it alone?should I leave it alone?• rebuild or replace?rebuild or replace?

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Rebuilding Wheel CylindersRebuilding Wheel Cylinders

• loosen the bleeder screw – this is loosen the bleeder screw – this is importantimportant

• cast iron cylinders can be honedcast iron cylinders can be honed aluminum cylinders should only be aluminum cylinders should only be

cleaned & not honedcleaned & not honed

• use brake fluid when honing use brake fluid when honing

• hone only enough to clean cylinder hone only enough to clean cylinder (≈10 seconds)(≈10 seconds)

• ensure there is no pitting where the cup ensure there is no pitting where the cup seals slideseals slide

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Rebuilding Wheel CylindersRebuilding Wheel Cylinders

• replace cup seals (note diameter) & dust bootsreplace cup seals (note diameter) & dust boots• use clean brake fluid or rubber lubricant to assembleuse clean brake fluid or rubber lubricant to assemble• reassembly – cups on seals face inwardreassembly – cups on seals face inward

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New Wheel CylindersNew Wheel Cylinders

• notice new brake line – olds ones notice new brake line – olds ones often twist when you loosen themoften twist when you loosen them

• use a use a flare nut wrenchflare nut wrench to loosen & to loosen & install hydraulic linesinstall hydraulic lines

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Lubricate Shoe Support PadsLubricate Shoe Support Pads

• use anti-seize compound on the 6 shoe support padsuse anti-seize compound on the 6 shoe support pads• this will reduce/eliminate brake squealthis will reduce/eliminate brake squeal• if the pads are groovedif the pads are grooved

replace backing plate, or…replace backing plate, or… mig weld grooves then grind smoothmig weld grooves then grind smooth

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Test Emergency Brake CablesTest Emergency Brake Cables

• apply & release e-brake while watching the cable move in & out apply & release e-brake while watching the cable move in & out of its’ housingof its’ housing

• any “laziness” or binding = cable needs replacingany “laziness” or binding = cable needs replacing

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Service Brake AdjusterService Brake Adjuster

• disassemble, clean threads & lubricate with anti-seize compounddisassemble, clean threads & lubricate with anti-seize compound• some imports use a wedge to spread the shoes apartsome imports use a wedge to spread the shoes apart• pay attention to the ends of the adjusterspay attention to the ends of the adjusters

ensure you understand how they are to be assembled ensure you understand how they are to be assembled

brake adjusters are side-specific – don’t mix up the left & right sides!

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Reinstall Brake ShoesReinstall Brake Shoes

• install new shoes install new shoes • use new hold down pins & springs if neededuse new hold down pins & springs if needed• dual-servo brakes (p. 835-837) will have unequal length brake dual-servo brakes (p. 835-837) will have unequal length brake

shoesshoes short shoe (primary) on the front side of the axleshort shoe (primary) on the front side of the axle long shoe (secondary) on the back side of the axlelong shoe (secondary) on the back side of the axle

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Install Upper Return SpringsInstall Upper Return Springs

• non-servo (leading-trailing) brakes will have a solid anchor at non-servo (leading-trailing) brakes will have a solid anchor at the bottom and equal length brake shoesthe bottom and equal length brake shoes

• replace the springs if rusted, kinked, bentreplace the springs if rusted, kinked, bent

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• conditions that require drum machining…conditions that require drum machining…

Drum Inspection & ReconditioningDrum Inspection & Reconditioning

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Drum Inspection & ReconditioningDrum Inspection & Reconditioning

• use a drum micrometer and check for oversizeuse a drum micrometer and check for oversize

• if drum is smooth and in otherwise good condition, simply if drum is smooth and in otherwise good condition, simply deglaze the brake surface with emery paperdeglaze the brake surface with emery paper

• machine drum if it is not oversizemachine drum if it is not oversize

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Adjusting Brake ShoesAdjusting Brake Shoes

• brake shoes will self-adjust for wear during normal operationbrake shoes will self-adjust for wear during normal operation some self-adjust when you back-up the vehiclesome self-adjust when you back-up the vehicle others self-adjust when you apply the hand brakeothers self-adjust when you apply the hand brake

• use a use a brake shoe setting gaugebrake shoe setting gauge for initial adjustment after for initial adjustment after replacing the brake shoesreplacing the brake shoes

• manipulate the adjuster (screw type or wedge) so that the manipulate the adjuster (screw type or wedge) so that the shoes will just contact the drumshoes will just contact the drum

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Adjusting the E-brakeAdjusting the E-brake

• afterafter the brake shoe-to-drum clearance has been adjusted, the the brake shoe-to-drum clearance has been adjusted, the e-brake cables can be adjusted e-brake cables can be adjusted if neededif needed

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• if bearings were removed, repack them with fresh wheel bearing if bearings were removed, repack them with fresh wheel bearing grease & replace the grease sealsgrease & replace the grease seals refer to chapter 34 in refer to chapter 34 in HaldermanHalderman

Wheel Bearing ServiceWheel Bearing Service

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Bleed / Flush Brake FluidBleed / Flush Brake Fluid

• if the hydraulic lines were disconnected or the wheel cylinder was if the hydraulic lines were disconnected or the wheel cylinder was

replaced/overhauled air has to be removed from the brake system replaced/overhauled air has to be removed from the brake system

as well as flushing out the old brake fluidas well as flushing out the old brake fluid

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Road Test the VehicleRoad Test the Vehicle

• ensure the pedal is high & firmensure the pedal is high & firm

• no noises or squeaksno noises or squeaks

• e-brake travel is correct amounte-brake travel is correct amount

• no brake fluid leaks at the wheel cylinder, line or bleeder valveno brake fluid leaks at the wheel cylinder, line or bleeder valve

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In the High SchoolIn the High School

• take a digital picture of the brakes before disassemblytake a digital picture of the brakes before disassembly place the pic on shop computer’s desktop for referenceplace the pic on shop computer’s desktop for reference

• print a diagram from Mitchellprint a diagram from Mitchell

• finish one side, then start the other sidefinish one side, then start the other side

• ensure you have sufficient time to complete the repairsensure you have sufficient time to complete the repairs