1990 GMC R2500 Suburban Brake Service (ONLINE REPAIR MANUALS)

DISASSEMBLE

• Remove pushrod clevis and locknut.
• Install brake booster to brake mounting fixture, Fig. . Ensure booster vacuum pipe is clear of mounting fixture base and the booster mounting nuts are not over tightened.
• Turn fixture handle until No. 1 and No. 2 body tabs are aligned, Fig. .
• Remove booster from fixture, then separate body No. 1 and No. 2. This step must be performed with care because there is spring pressure between body No. 1 and No. 2.
• Remove booster piston spring, piston rod, boot, air cleaner and air cleaner separator from body No. 2.
• Remove valve stopper key cush...

EXCEPT TRACKER & 1990-91 C & K SERIES w/NON-SERVO BRAKES

• Raise and support vehicle, then remove tire and wheel assembly.
• Remove brake drum. If brake lining is dragging on brake drum, back off brake adjustment by rotating adjustment screw. Refer to individual truck chapter for procedure. If brake drum is rusted or corroded to axle flange and cannot be removed, lightly tap flange to drum mounting surface with a suitable hammer.
• Using brake spring pliers or equivalent, unhook primary and secondary return springs, Figs. through . Observe location of brake parts being removed to aid during ins...

The height sensing proportioning valve must be adjusted whenever the valve and/or linkage is disassembled or removed for service. In addition, adjustment should be checked if excessive front wheel lock-up is experienced with a lower than desired brake application rate when vehicle is at or near maximum GVWR.

• Raise and support vehicle leaving wheels on, and allow axle to hang free (no load condition).
• Remove lever retaining nut and disconnect lever from valve shaft, Fig. .
• Rotate valve shaft to permit installation of correct adjustment gauge, Fig. ,...

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...

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...

CABALLERO & EL CAMINO

• Remove vacuum hose from check valve and master cylinder retaining nuts.
• Pull master cylinder forward so it clears mounting studs and move to one side. Support cylinder to avoid stress on hydraulic lines.
• Remove power unit to dash nuts.
• Remove brake pedal pushrod retainer and disconnect pushrod from pin.
• Remove power brake unit from vehicle.
• Reverse procedure to install.

ASTRO & SAFARI VAN

• Disconnect master cylinder from power brake unit.
• Disconnect power brake unit pushrod from brake pedal.
• Remove power brake unit retaining nuts and the power brake unit.
• Rev...