1990 Chevrolet P30 VAN Brake Service (ONLINE REPAIR MANUALS)

When working on or around brake assemblies, care must be taken to prevent breathing asbestos dust, as many manufacturers incorporate asbestos fibers in the production of brake linings. During routine service operations, the amount of asbestos dust from brake lining wear is at a low level due to a chemical breakdown during use, and a few precautions will minimize exposure. Do not sand or grind brake linings unless suitable local exhaust ventilation equipment is used to prevent e...

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...

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...

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...

WIRING DIAGRAMS

Refer to "Wiring Diagrams" in "Vehicle Systems."

READING TROUBLE CODES

Trouble codes are accessed by connecting a jumper wire between terminals A and H of the underdash ALDL connector and observing the flashes of the brake warning lamp. Note the following when performing the Diagnostic Circuit Check to access trouble codes.

• When the terminals are jumped, count the number of short flashes starting from the initial long flash and including the long flash in the count.
• The count sequence will repeat as long as the ALDL connector terminals are jumped with the ignition on.
• ...

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...