1990 Pontiac Bonneville 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 excessive asbestos exposure.
• Wear a suitable respirator approved for asbestos dust use during all repai...

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. Mi...

DESCRIPTION

This unit utilizes a vacuum power chamber, consisting of a front and rear shell, housing divider, front and rear diaphragm, plate assemblies, hydraulic pushrod and a diaphragm return spring,Figs. and .

The unit operates in much the same manner as the single diaphragm unit described previously. The diaphragm and plate assemblies utilize the pressure differential between the engine intake manifold vacuum and atmospheric pressure to assist in braking.

TROUBLESHOOTING

Hard Pedal

• Internal vacuum leak.
• Faulty control valve.

Brakes Grab

• Faulty control valve...

Servicing of disc brakes is extremely critical due to the close tolerances required in machining the brake disc to insure proper brake operation.

The maintenance of these close controls of the shape of the rubbing surfaces is necessary to prevent brake roughness. In addition, the surface finish must be non-directional and maintained at a micro inch finish. This close control of the rubbing surface finish is necessary to avoid pulls and erratic performance, and to promote long lining life and equal lining wear of both left and right brakes.

In light of the foregoing remarks, ref...

DUAL MASTER CYLINDER

Front & Rear Split System

When the brake pedal is depressed, both the primary (front brake) and the secondary (rear brake) master cylinder pistons are moved simultaneously to exert hydraulic fluid pressure on their respective systems,Figs. and .

If the rear (secondary) brake system fails, initial brake pedal movement will cause the unrestricted secondary piston to bottom in the master cylinder bore. Primary piston movement will displace hydraulic fluid in the primary section of the master cylinder to actuate the front brake system.

If the front (primary) brak...

DEPRESSURIZING HYDRAULIC ACCUMULATOR

Depressurize accumulator before performing any ABS service.

• Disconnect battery ground cable or place ignition switch in the Off position.
• Apply and release brake pedal a minimum of 20 times using approximately 50 lbs. of force on pedal. A noticeable change in pedal feel will occur when accumulator is completely discharged. If battery negative cable was disconnected, reactivate Delco-Loc radios by turning ignition and radio to the On position, then pressing the Mute button on the steering wheel control.

BRAKE SYSTEM FILLING

Ensure pump is not allowe...