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Brakes

Brake Diagnosis: Low, Soft or No Pedal Conditions

 

  • LOW, SOFT or NO PEDAL conditions may not be caused by a failing master cylinder. These symptoms may be indicative of a failure in an ABS unit, vacuum booster unit, soft brake hoses, contaminated brake fluid or air trapped in the system.
  • The use of line locks (NOT VISE GRIPS) on all brake hoses will allow you to determine whether the problem is at the wheels or higher in the hydraulic system. With locks installed on front and rear hoses, re-check the brake pedal condition. If a low or no pedal condition persists, the problem is between the line locks and the master cylinder. If the brake pedal is high and hard with the line locks on, hold pressure on brake pedal and remove line locks one at a time until the pedal drops. This will identify which wheel or wheels are causing the problem. The use of line locks helps prevent the needless replacement of master cylinders. Line locks have been known to damage brake hoses and should not be used routinely for preventing fluid loss.
  • Use master cylinder outlet plugs to isolate master cylinder problems, i.e. rear anti-lock modulator valves.
  • When bench bleeding a unit, use a syringe part #MT-6130 (to reverse bleed) to expel all air from new master cylinder or a vacuum bleeder to suction fluid through the cylinder bore. Be sure to use NEW & CLEAN fluid only. Be sure to use the proper bleeding procedure for the vehicle you are working on.
  • CAUTION: Avoid over-stroking and rapid pedal movement during foot bleeding. The entire system should be flushed when any major repair is done, i.e. master cylinder, wheel cylinders, calipers, etc. The recommended service interval for brake fluid is 2 years or 30,000 miles, whichever comes first.
  • Many ABS systems require special procedures and precautions. Refer to the appropriate service manual before major repairs are undertaken.

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