1990 GMC K2500 Pickup Brake Service (ONLINE REPAIR MANUALS)

REMOVAL

• Siphon enough brake fluid out of the master cylinder to bring fluid level to^1-3 full to avoid fluid overflow when the caliper piston is pushed back into its bore.
• Raise and support vehicle, remove front wheels.
• Using a C-clamp, as illustrated in Fig. , push piston back into its bore.
• Remove two mounting bolts and lift caliper away from disc.

DISASSEMBLE

• Disconnect hose from the caliper being careful not to lose copper washers.
• Remove caliper as outlined above.
• Drain brake fluid from caliper.
• Pad caliper interior with clean shop towels and apply compressed air to remove piston, Fi...

REMOVAL

• Remove caliper assembly as outlined above.
• Remove inboard pad with retainer spring. Dislodge outboard pad and position caliper on the front suspension so the brake hose will not support the weight of the caliper.
• Remove two sleeves from inboard ears of the caliper.
• Remove four rubber bushings from the grooves in each of the caliper ears.

INSTALLATION

• Lubricate new sleeves, rubber bushings, bushing grooves and mounting bolt ends with Delco Silicone Lube or equivalent.
• Install new bushings and sleeves in caliper ears. Position the sleeve so that the end toward the pad is flush...

DELCO MORAINE TYPE

COMPOSITE TYPE

Refer to Figs. and when performing the following procedures.

Disassemble

• Remove master cylinder from vehicle.
• Remove reservoir cover and diaphragm. Discard old brake fluid in reservoir.
• Inspect cover and diaphragm. Replace if cut, cracked or deformed.
• Remove fluid level switch and proportioner valve assembly, if equipped.
• Depress primary piston and remove lock ring.
• Plug primary fluid outlet (outlet nearest to cowl when master cylinder is installed), then apply compressed air into secondary fluid outlet to remove primary and secondary pistons.
• R...

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...

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 ...

REMOVAL

• Siphon two-thirds of brake fluid from master cylinder reservoir serving front disc brakes.
• Raise vehicle, support on jack stands and remove front wheels.
• Bottom the caliper piston in bore. Insert a screwdriver between inboard shoe and piston, then pry piston back into bore. The piston can also be bottomed in the bore with a large C-clamp, Fig. .
• Remove support key retaining screw.
• Drive caliper support key and spring from steering knuckle with a suitable drift and hammer, Fig. .
• Lift caliper from anchor plate and off rotor, Fig. . Hang caliper from coil spring with wire. Do n...