GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1997 🢒 GMC P62 Commercial Chassis 🢒 Brakes 🢒 Hydraulic Brakes 🢒 Brake System Diagnosis

Excessive Brake Pedal Travel

Checks

Action

Preliminary Check

Check for air in the hydraulic system. Refer to Bleeding The Brake Hydraulic System.

Additional Checks
    • Check for leaks in brake pipes, in brake hoses, and at connections. Refer to Brake Fluid Leaks.
    • Check for leaks at piston seals. Refer to Seal Leak Diagnosis.
    • Check for leaks at the master cylinder. Refer to Master Cylinder.
    • Check for contaminated or improper brake fluid. Refer to Substandard or Contaminated Brake Fluid.
    • Check for uneven wear of the brake linings.
    • Check for improper variations in the thickness of the brake linings.
    • Check for excessive lateral runout.
    • Check for missing or loose attachments to the brake assembly.

Brake Pedal Travel Gradually Increases

Checks

Action

Preliminary Checks
    • Check for leaks in brake pipes, in brake hoses, and at connections. Refer to Brake Fluid Leaks.
    • Check for leaks at piston seals. Refer to Seal Leak Diagnosis
    • Check for leaks at the master cylinder. Refer to Master Cylinder.

Additional Checks
    • Check for a restricted passage in the hydraulic booster.
    • Check for damage to the hydraulic booster.
    • Check for improper variation in the thickness of the brake linings.
    • Check for excessive lateral runout.
    • Check for restrictions in the passage of brake fluid.

Excessive Brake Pedal Effort

Checks

Action

Preliminary Checks
    • Check for leaks in the hydraulic booster system. Refer to Hydraulic Booster System Fluid Loss.
    • Check for glazed brake linings.

Additional Checks
    • Check for a restricted passage in the hydraulic booster.
    • Check for damage to the hydraulic booster.
    • Check for worn-out brake linings.
    • Check for brake linings of an incorrect material.
    • Check for contaminated brake linings.
    • Check for brake linings that have been damaged by abuse.
    • Check for restricted passages of brake fluid.
    • Check for interference or binding in the brake pedal linkage. Refer to Brake Pedal Linkage.
    • Check to see if the driver rides the brake pedal.
    • Check the finish on the rotor surface.

Excessive Braking Action

Checks

Action

Preliminary Check

Check for brake linings that have been damaged by abuse.

Additional Checks
    • Check for damage to the hydraulic booster.
    • Check for worn-out brake linings.
    • Check for brake linings that have uneven wear.
    • Check for brake lining of an incorrect material.
    • Check for brake discs that are heat-spotted or scored.
    • Check for missing or loose attachments to the brake assembly.

Brakes Are Slow To Respond

Checks

Action

Preliminary Check

Check for a restricted passage in the hydraulic booster.

Additional Checks
    • Check for contaminated or improper brake fluid. Refer to Substandard or Contaminated Brake Fluid.
    • Check for leaks in the hydraulic booster system. Refer to Hydraulic Booster System Fluid Loss.
    • Check for brake linings that are glazed.
    • Check for restricted passage of brake fluid.
    • Check for interference or binding in the brake pedal linkage.
    • Check for binding in the caliper or caliper pistons.

Brakes Are Slow To Release

Checks

Action

Preliminary Checks
    • Check for damage to the hydraulic booster.
    • Check for interference or binding in the brake pedal linkage.

Additional Checks
    • Check for contaminated or improper brake fluid. Refer to Substandard or Contaminated Brake Fluid.
    • Check for a restricted passage in the hydraulic booster.
    • Check for a restricted passage of brake fluid.
    • Check for binding calipers or caliper pistons
    • Check for a stuck parking brake.

Brakes Drag

Checks

Action

Preliminary Checks
    • Check for interference or binding in the brake pedal linkage. Refer to Brake Pedal Linkage.
    • Check for binding calipers or caliper pistons.

Additional Checks
    • Check for contaminated or improper brake fluid. Refer to Substandard or Contaminated Brake Fluid.
    • Check for missing or loose attachments to the brake assembly.
    • Check for a restricted passage of brake fluid.
    • Check for an improperly adjusted stoplamp switch. Refer to Stoplamp Switch Adjustment.
    • Check for an improperly adjusted parking brake.
    • Check for loose attachments to the front suspension.
    • Check to see if the driver rides the brake pedal.

Uneven Braking Action (Side to Side)

Checks

Action

Preliminary Checks
    • Check for contaminated brake linings.
    • Check for incorrect front end alignment

Additional Checks
    • Check for contaminated or improper brake fluid. Refer to Substandard or Contaminated Brake Fluid.
    • Check for worn-out brake linings.
    • Check for uneven wear of the brake linings.
    • Check for brake linings that are glazed.
    • Check for brake linings of an incorrect material.
    • Check for brake linings that have been damaged by abuse.
    • Check for brake discs that are heat-spotted or scored. Check for missing or loose attachments to the brake assembly
    • Check for a restricted passage of brake fluid
    • Check for an improperly adjusted parking brake.
    • Check for incorrect tire pressure.
    • Check for loose attachments to the front suspension. Check for binding calipers or caliper pistons.
    • Check for a stuck parking brake.

Uneven Braking Action (Front to Rear)

Checks

Action

Preliminary Check

Check for contaminated brake linings.

Additional Checks
    • Check for leaks in brake pipes, in brake hoses, or at connections. Refer to Brake Fluid Leaks.
    • Check for leaks at piston seals. Refer to Seal Leak Diagnosis
    • Check for leaks at the master cylinder. Refer to Master Cylinder.
    • Check for air in the hydraulic system. Refer to Bleeding the Brake Hydraulic System.
    • Check for contaminated or improper brake fluid. Refer to Substandard or Contaminated Brake Fluid.
    • Check for worn-out brake linings.
    • Check for uneven wear of the brake linings.
    • Check for brake linings that are glazed.
    • Check for brake linings of an incorrect material.
    • Check for brake linings that have been damaged by abuse.
    • Check for brake discs that are heat-spotted or scored.
    • Check for missing or loose attachments to the brake assembly.
    • Check for a restricted passage of brake fluid.
    • Check for an improperly adjusted parking brake.
    • Check for binding calipers or caliper pistons.

Scraping Noise From Brakes

Checks

Action

Preliminary Check

Check for loose attachments to the front suspension.

Additional Checks
    • Check for worn-out brake linings.
    • Check for brake linings that have uneven wear.
    • Check for contaminated brake linings.
    • Check for brake linings that have been damaged by abuse.
    • Check for missing or loose attachments to the brake assembly.

Brakes Squeak During Application

Checks

Action

Preliminary Checks
    • Check for worn-out brake linings.
    • Check for brake linings that have uneven wear.
    • Check for brake linings that are glazed.
    • Check for brake linings of an incorrect material.
    • Check for contaminated brake linings.
    • Check for brake linings that have been damaged by abuse.
    • Check for brake discs that are heat-spotted or scored.

Brakes Squeak During Stop

Checks

Action

Preliminary Check

Check for brake linings that have uneven wear.

Additional Checks
    • Check for worn-out brake linings.
    • Check for brake linings that are glazed.
    • Check for brake linings of an incorrect material.
    • Check for contaminated brake linings.
    • Check for brake linings that have been damaged by abuse.
    • Check for brake discs that are heat-spotted or scored.
    • Check for missing or loose attachments to the brake assembly.

Brakes Chatter (Roughness)

Checks

Action

Preliminary Checks
    • Check for brake discs that are heat-spotted or scored.
    • Check for improper variation in the thickness of the brake lining.

Additional Checks
    • Check for excessive lateral runout
    • Check for missing or loose attachments to the brake assembly.

Brakes Groan at the End of a Stop

Checks

Action

Preliminary Check

Check for wheel assemblies that are out of balance.

Additional Checks
    • Check for brake linings that have been damaged by abuse.
    • Check for loose attachments to the front suspension.

"BRAKE" Warning Lamp Stays Lit

Checks

Action

Preliminary Checks
    • Check for leaks in the brake pipes, in the brake hoses, or at connections. Refer to Brake Fluid Leaks.
    • Check for air in the hydraulic system. Refer to Bleeding the Brake Hydraulic System.
    • Check for a short to ground in the parking brake switch circuit.
    • Check for a stuck parking brake.

Additional Checks
    • Check for leaks at the piston seal. Refer to Seal Leak Diagnosis.
    • Check for leaks at the master cylinder. Refer to Master Cylinder.
    • Check for contaminated or improper brake fluid. Refer to Substandard or Contaminated Brake Fluid.
    • Check for worn-out brake linings.
    • Check for brake linings that have uneven wear.