1991 Chevrolet R1500 Suburban Brake Service (ONLINE REPAIR MANUALS)

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 (...

Certain general service procedures apply, regardless of whether the brakes are vacuum or hydraulically assisted. Only top quality, clean brake fluid should be used. More seals and valves are used with power brake systems than with ordinary brakes, so an inferior brake fluid will do much more damage. For the same reason, be sure all dirt is kept out of the system. Additionally, on models with hydraulic assist brakes, care must be taken not to mix the fluids of the booster hydraulic system and brake hydraulic system as the fluids are not compatible.

If the power unit fai...

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...

DESCRIPTION

The Hydro-Boost system, Fig. , provides an additional cylinder in the brake system. This cylinder contains no brake fluid. The Hydro-Boost cylinder is hydraulically operated, by pressurized fluid from the power steering pump, providing power assist to operate a dual master cylinder brake system.

The booster is composed of two sections; the linkage section and the power section.

The booster is designed so that if a total absence of power assist occurs, the brakes can be applied manually, but somewhat greater pressure on the brake pedal is required.

DISASSEMBLE

• Place accumulato...

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 DRUMS

Any time the brake drums are removed for brake service, the braking surface diameter should be checked with a suitable brake drum micrometer at several points to determine if they are within the safe oversize limit stamped on the brake drum outer surface. If the braking surface diameter exceeds specifications, the drum must be replaced. If the braking surface diameter is within specifications, drums should be cleaned and inspected for cracks, scores, deep grooves, taper, out of round and heat spotting. If drums are cracked or heat spotted, they must be replaced. Gr...