1990 GMC K1500 Pickup Brake Service (ONLINE REPAIR MANUALS)

SLOW BRAKE PEDAL RETURN

• Excessive seal friction in booster.
• Faulty spool action.
• Restriction in return line from booster to pump reservoir.
• Damaged input rod end.

GRABBY BRAKES OR BOOSTER CHATTERS/PEDAL VIBRATES

• Faulty spool action caused by contamination in ...

• Raise and support vehicle.
• Remove wheel, drum and brake shoes.
• Disconnect hydraulic line at wheel cylinder. Do not pull metal line away from cylinder, as this may kink or bend line. Line will separate from cylinder when cylinder is moved away from brake backing plate.
• Remove wheel cylinder-to-brake plate attaching screws, then the wheel cylinder.
• Remove boots, pistons, springs and cups from cylinder, Fig. .
• Clean all parts with brake fluid.
• Inspect cylinder bore. A scored bore may be honed as long as the diameter is not increased by ...

CABALLERO & EL CAMINO

Pump brake pedal several times with engine off to deplete accumulator of fluid.

• Remove two nuts attaching master cylinder to booster, then move master cylinder away from booster with brake lines attached.
• Remove three hydraulic lines from booster. Plug and cap all lines and outlets.
• Remove retainer and washer securing booster pushrod to brake pedal arm.
• Remove four nuts attaching booster unit to dash panel.
• From engine compartment, loosen booster from dash panel and move booster pushrod inboard until it disconnects from brake pedal arm. Remove spring wa...

In order to properly service power brake systems, a thorough understanding of the various power assist systems is necessary. These systems provide a mechanical assist, acting to increase the force applied to the master cylinder piston by the driver while decreasing the effort necessary to obtain acceptable stopping performance. Two basic types of power assist mechanisms are used: vacuum assist diaphragm assemblies which use engine vacuum and in some cases vacuum from an external vacuum pump, and hydraulic assist assemblies which use hydraulic pressure developed by an external pump (...

MASTER CYLINDER

Some vehicles use a conventional tandem master cylinder with two hydraulic pistons operating in line. The primary piston controls the front brake system and the secondary piston controls the rear brake system.

Other models use a master cylinder that operates the same as the conventional master cylinder, but also incorporates a quick take-up feature in the rear chamber to reduce excessive pedal travel which may result from increased fluid displacement required to move the low drag caliper piston out against the rotor.

The quick take-up uses a spring-loaded ball...

BRAKE LINES & LININGS

Remove one of the front wheels and inspect the brake disc, caliper and linings.

Do not get any oil or grease on the linings. It is recommended that all linings be replaced in sets when worn or damaged.

If the caliper is cracked or fluid leakage through the casting is evident, it must be replaced as a unit.

BRAKE ROUGHNESS

The most common cause of brake chatter on disc brakes is a variation in thickness of the disc. If roughness or vibration is encountered during highway operation or if pedal pumping is experienced at low speeds, the disc may have excessive t...