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Brake System Problem DiagnosisBrake System Problem Diagnosis&&

ABS Service TipsABS Service Tips

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Brake SquealBrake Squeal• is usually the result of high frequency metal-to-metal vibrationis usually the result of high frequency metal-to-metal vibration• on drum brakes…on drum brakes…

ensure the 6 brake shoe support pads have a thin coat of high temp lube such as ensure the 6 brake shoe support pads have a thin coat of high temp lube such as anti-seize compoundanti-seize compound

• on disc brakes…on disc brakes… ensure brake shims are used on the brake pad backingsensure brake shims are used on the brake pad backings check abutment clips – replace if neededcheck abutment clips – replace if needed clean & lubricate the caliper slidesclean & lubricate the caliper slides alternate brake pad composition may helpalternate brake pad composition may help

organicorganic semi-metallicsemi-metallic ceramicceramic

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Brake Pedal Pulsation or Steering Wheel ShimmyBrake Pedal Pulsation or Steering Wheel Shimmy

• front brake rotors need refinishing or replacementfront brake rotors need refinishing or replacement wheel installation with an impact gun can cause thiswheel installation with an impact gun can cause this hard, panic stops when the brakes are hot can lead to these conditionshard, panic stops when the brakes are hot can lead to these conditions

• remember to measure the disc thickness to determine if there is enough material left to remember to measure the disc thickness to determine if there is enough material left to machinemachine

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Low Brake PedalLow Brake Pedal

• this is usually caused by either…this is usually caused by either…

1) brake shoes are out of adjustment1) brake shoes are out of adjustment (shoes are too far away from drum)(shoes are too far away from drum)

2) air in the hydraulic lines 2) air in the hydraulic lines if this is the case YOU HAVE A BRAKE FLUID LEAK!!!if this is the case YOU HAVE A BRAKE FLUID LEAK!!! air in the system is not a normal condition!air in the system is not a normal condition! brake fluid level should never get below the MIN markbrake fluid level should never get below the MIN mark

brake warning lamp may be illuminatedbrake warning lamp may be illuminated

pump the brake pedal rapidly 3 or 4 timespump the brake pedal rapidly 3 or 4 times if the pedal came up higher: shoe adjustment issueif the pedal came up higher: shoe adjustment issue if the pedal is still low: air in the line(s)if the pedal is still low: air in the line(s)

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Brakes Pull to One SideBrakes Pull to One Side

• ensure it is not the steering system creating the pullensure it is not the steering system creating the pull if it pulls with the brakes off – it is most likely in the steering system & if it pulls with the brakes off – it is most likely in the steering system & notnot the the

brakesbrakes

• one of the front calipers isn’t working properlyone of the front calipers isn’t working properly rebuild or replace calipersrebuild or replace calipers

• restricted front brake flex hoserestricted front brake flex hose prevents brake fluid from becoming pressurizedprevents brake fluid from becoming pressurized

• pulling is pulling is notnot the result of metering valve, proportioning valve or ABS problems the result of metering valve, proportioning valve or ABS problems

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Dragging Brake(s)Dragging Brake(s)

• can be associated with sluggish vehicle performancecan be associated with sluggish vehicle performance• brakes will smell when overheatedbrakes will smell when overheated• can be a caliper piston is not retractingcan be a caliper piston is not retracting• e-brake cable is not releasing completelye-brake cable is not releasing completely• drum brake shoes adjusted too close to the drumdrum brake shoes adjusted too close to the drum• can be caused by a collapsed flex hosecan be caused by a collapsed flex hose

this allows brake fluid to pressurizethis allows brake fluid to pressurize but when pedal is released fluid is “trapped” under pressure and piston can’t retractbut when pedal is released fluid is “trapped” under pressure and piston can’t retract

loosen the bleeder to determine if this is the causeloosen the bleeder to determine if this is the cause

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Brakes Grab / Lock-upBrakes Grab / Lock-up

• if both rear brakes grab, front brakes should be inspected carefullyif both rear brakes grab, front brakes should be inspected carefully proportioning valve limits pressure to rear wheelsproportioning valve limits pressure to rear wheels if front brakes aren’t functioning correctly then rear brakes will have to work harder if front brakes aren’t functioning correctly then rear brakes will have to work harder

to stop the vehicleto stop the vehicle with the transfer of weight from back to front on hard braking, this can lead to rear with the transfer of weight from back to front on hard braking, this can lead to rear

wheel lock-upwheel lock-up• this is usually the result of oil, grease or brake fluid on the brake liningsthis is usually the result of oil, grease or brake fluid on the brake linings

replace defective grease seal, wheel cylinder or axle sealreplace defective grease seal, wheel cylinder or axle seal

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Brake Pedal SinksBrake Pedal Sinks

• you are stopped at a red light & the pedal is at its normal heightyou are stopped at a red light & the pedal is at its normal height• slowly, the pedal starts to sink to the floorslowly, the pedal starts to sink to the floor• you quickly pump up the pedal & it returns to normal heightyou quickly pump up the pedal & it returns to normal height• again it starts to sinkagain it starts to sink• this is caused by…this is caused by…

an internal leak in the master cylinderan internal leak in the master cylinder fluid is leaking past the primary seal(s)fluid is leaking past the primary seal(s)

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ABS System Service…ABS System Service…

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ABS System Diagram

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Servicing PrecautionsServicing Precautions

• bleeding (removing air from hydraulic lines) & flushing brake fluidbleeding (removing air from hydraulic lines) & flushing brake fluid may be done exactly the same as a non-ABS equipped vehiclemay be done exactly the same as a non-ABS equipped vehicle or may have specific bleeding procedures which or may have specific bleeding procedures which

• when disconnecting brake lines, accumulator pressure may have to be relieved – can be when disconnecting brake lines, accumulator pressure may have to be relieved – can be up to 2800 PSI!up to 2800 PSI! pumping the brake pedal 30 to 40 times with engine off may be necessarypumping the brake pedal 30 to 40 times with engine off may be necessary

• read manufacturer's instructions carefully before beginning repairs!read manufacturer's instructions carefully before beginning repairs!

• ABS problem: always begin with a thorough inspection of the base brake system (non-ABS ABS problem: always begin with a thorough inspection of the base brake system (non-ABS portion) firstportion) first

• brake warning light indicates a problem in the base braking system – not the ABSbrake warning light indicates a problem in the base braking system – not the ABS

• ABS warning lamp indicates a problem within the ABSABS warning lamp indicates a problem within the ABS

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Warning LightsWarning Lights• both brake warning lights should come on for about 6 seconds when the ignition is both brake warning lights should come on for about 6 seconds when the ignition is

initially turned oninitially turned on this confirms that the warning circuit is operationalthis confirms that the warning circuit is operational

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Service TipsService Tips• check wheel speed sensors for debris build-up (permanent check wheel speed sensors for debris build-up (permanent

magnet)magnet)• check sensor wiring & connectorscheck sensor wiring & connectors

frayed insulationfrayed insulation incorrect routing can chafe wiringincorrect routing can chafe wiring loose, corroded connectorsloose, corroded connectors

Service TipsService Tips

• check tone rings for damage/debris build-upcheck tone rings for damage/debris build-up

• mismatched tire sizes will confuse the EBCMmismatched tire sizes will confuse the EBCM

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• follow manufacturer’s repair procedures carefully…follow manufacturer’s repair procedures carefully…

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Service TipsService Tips

• when replacing brake pads, when replacing brake pads, do notdo not push caliper pistons in without loosening bleeder screw push caliper pistons in without loosening bleeder screw

this prevents dirt from being pushed out of the caliper & into the brake modulator & this prevents dirt from being pushed out of the caliper & into the brake modulator &

master cylindermaster cylinder

• regular brake fluid flushes (every 2 years) will minimize modulator & solenoid problems & regular brake fluid flushes (every 2 years) will minimize modulator & solenoid problems &

extend their life spanextend their life span