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Brake System Problem Diagnosis & ABS Service Tips

Brake System Problem Diagnosis & ABS Service Tips. R. Bortignon. Brake Squeal. is usually the result of high frequency metal-to-metal vibration on drum brakes… ensure the 6 brake shoe support pads have a thin coat of high temp lube such as anti-seize compound on disc brakes…

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Brake System Problem Diagnosis & ABS Service Tips

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  1. Brake System Problem Diagnosis&ABS Service Tips R. Bortignon

  2. Brake Squeal • is usually the result of high frequency metal-to-metal vibration • on drum brakes… • ensure the 6 brake shoe support pads have a thin coat of high temp lube such as anti-seize compound • on disc brakes… • ensure brake shims are used on the brake pad backings • check abutment clips – replace if needed • clean & lubricate the caliper slides • alternate brake pad composition may help • organic • semi-metallic • ceramic

  3. Brake Pedal Pulsation or Steering Wheel Shimmy • front brake rotors need refinishing or replacement • wheel installation with an impact gun can cause this • hard, 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 machine

  4. Low Brake Pedal • this is usually caused by either… 1) brake shoes are out of adjustment • (shoes are too far away from drum) 2) air in the hydraulic lines • if this is the case YOU HAVE A BRAKE FLUID LEAK!!! • air in the system is not a normal condition! • brake fluid level should never get below the MIN mark • brake warning lamp may be illuminated • pump the brake pedal rapidly 3 or 4 times • if the pedal came up higher: shoe adjustment issue • if the pedal is still low: air in the line(s)

  5. Brakes Pull to One Side • ensure it is not the steering system creating the pull • if it pulls with the brakes off – it is most likely in the steering system & not the brakes • one of the front calipers isn’t working properly • rebuild or replace calipers • restricted front brake flex hose • prevents brake fluid from becoming pressurizing • pulling is not the result of metering valve, proportioning valve or ABS problems

  6. Dragging Brake(s) • can be associated with sluggish vehicle performance • brakes will smell when overheated • can be a caliper piston is not retracting • e-brake cable is not releasing completely • drum brake shoes adjusted too close to the drum • can be caused by a collapsed flex hose • this allows brake fluid to pressurize • but when pedal is released fluid is “trapped” under pressure and piston can’t retract • loosen the bleeder to determine if this is the cause

  7. Brakes Grab / Lock-up • if both rear brakes grab, front brakes should be inspected carefully • proportioning valve limits pressure to rear wheels • if front brakes aren’t functioning correctly then rear brakes will have to work harder to stop the vehicle • with the transfer of weight from back to front on hard braking, this can lead to rear wheel lock-up • this is usually the result of oil, grease or brake fluid on the brake linings • replace defective grease seal, wheel cylinder or axle seal

  8. Brake Pedal Sinks • Imagine this… • you are stopped at a red light & the pedal is at its normal height • slowly, the pedal starts to sink to the floor • you quickly pump up the pedal & it returns to normal height • again it starts to sink • this is caused by… • an internal leak in the master cylinder • fluid is leaking past the primary seal(s)

  9. ABS System Service…

  10. ABS System Diagram

  11. Servicing Precautions • bleeding (removing air from hydraulic lines) & flushing brake fluid • may be done exactly the same as a non-ABS equipped vehicle • or may have specific bleeding procedures which • when disconnecting brake lines, accumulator pressure may have to be relieved – can be up to 2800 PSI! • pumping the brake pedal 30 to 40 times with engine off may be necessary • read manufacturer's instructions carefully before beginning repairs! • ABS problem: always begin with a thorough inspection of the base brake system (non-ABS portion) first • brake warning light indicates a problem in the base braking system – not the ABS • ABS warning lamp indicates a problem within the ABS

  12. Warning Lights • both brake warning lights should come on for about 5 seconds when the ignition is initially turned on • this confirms that the warning circuit is operational

  13. Service Tips • check wheel speed sensors for debris build-up (permanent magnet) • check sensor wiring & connectors • frayed insulation • incorrect routing can chafe wiring • loose, corroded connectors

  14. Service Tips check tone rings for damage/debris build-up mismatched tire sizes will confuse the EBCM

  15. follow manufacturer’s repair procedures carefully…

  16. Service Tips • when replacing brake pads, do not push caliper pistons in without loosening bleeder screw • this prevents dirt from being pushed out of the caliper & into the brake modulator & master cylinder • regular brake fluid flushes (every 2 years) will minimize modulator & solenoid problems & extend their life span

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