1990 Chevrolet C2500 Pickup Brake Service (ONLINE REPAIR MANUALS)

DESCRIPTION

Hydro-Boost II is an hydraulically operated power brake booster. The hydraulic brake booster consists of an open center spool valve and an hydraulic cylinder combined into a single housing. The power steering pump provides the hydraulic fluid pressure to operate both the power brake booster and the power steering gear.

A dual master cylinder is bolted to the brake booster and is operated by a pushrod projecting from the booster cylinder bore.

The Hydro-Boost II also has an accumulator system which stores sufficient fluid under pressure to provide one power assisted brake...

EXCESSIVE PEDAL TRAVEL

• Worn brake linings.
• Disc pads knock back after cornering or rough road travel.
• Piston and linings not properly seated or positioned.
• Insufficient fluid in system.
• Loose wheel bearing adjustment.
• Damaged or worn caliper piston seal.
• Improper booster pushrod adjustment.
• Pads out of flat more than .005 inch.
• Rear brake automatic adjusters inoperative.
• Improperly ground rear brake shoes.

BRAKE ROUGHNESS OR CHATTER; PEDAL PUMPING

• Excessive lateral runout of rotor.
• Rotor excessively out of parallel.

EXCESSIVE PEDAL EFFORT

• Frozen or seized pistons.
• Brake fluid, oil or grease on ...

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. ,...

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 (...

The procedures to remove & install the brake pads are outlined under "Caliper Service," "Remova... "

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...