Brakes - Diagnosis

The following diagnosis applies to both power brakes and standard brakes unless otherwise specified.

  1. Hard Pedal Feel May Be Caused By:
    1. Power brake vacuum failure due to:
      1. Faulty vacuum check valve or seal.
      2. Collapsed vacuum hose to manifold.
      3. Plugged or loose vacuum hose or fitting.
      4. Leaks in front or rear housing.
    2. Bound up pedal mechanism.
    3. Grease on brake drum or linings.
    4. Power brake unit trouble due to:
      1. Jammed air valve.
      2. Vacuum leak past the vacuum diaphragm.
      3. Leak in vacuum cylinder.
      4. Restricted air filter.
      5. Malfunctioning air valve.
      6. Leaking past floating or air valve.
  2. "Grabby" or Severe Brakes Caused By:
    1. Grease or brake fluid on linings.
    2. Scored drums.
    3. Burned linings.
    4. Power brake unit trouble due to:
      1. Sticking air valve.
      2. Binding master cylinder piston.
  3. Pedal Goes to Floor (or almost to floor) Caused By:
    1. Self-adjuster not operating.
    2. Air in hydraulic system.
    3. Hydraulic leak in line or at wheel cylinders.
    4. Low fluid level in master cylinder reservoir.
    5. Leak at primary cup.
    6. Sand hole or crack in master cylinder.
    7. Worn brake linings.
  4. Brake Lock-Up Caused By:
    1. Restricted compensator port.
    2. Incorrect push-rod adjustment (Power).
    3. Incorrect pedal free travel (Standard).
    4. Faulty hydraulic check valve.
    5. Sticking air valve.
  5. Excessive Lining Wear Rear Brakes
    1. Parking brake improperly adjusted.