1991 Oldsmobile 98 Brake Service (ONLINE REPAIR MANUALS)

• Raise and support vehicle.
• Remove wheel, drum and brake shoes.
• Disconnect hydraulic line at wheel cylinder.Do not pull metal line away from cylinder, as this may kink or bend line. Line will separate from cylinder when cylinder is moved away from brake backing plate.
• Remove wheel cylinder-to-brake plate attaching screws, then the wheel cylinder.
• Remove boots, pistons, springs and cups from cylinder,Fig. .
• Clean all parts with brake fluid.
• Inspect cylinder bore. A scored bore may be honed as long as the diameter is not increased by m...

COMPOSITE TYPE

Refer toFigs. and when performing the following procedures.

EXCEPT CORVETTE

Disassembly

• Remove master cylinder from vehicle as follows:
• Disconnect and plug hydraulic lines.
• Remove two master cylinder attaching nuts, then the master cylinder.
• Remove reservoir cover and diaphragm. Discard old brake fluid in reservoir.
• Inspect cover and diaphragm. Replace if cut, cracked or deformed.
• Remove fluid level switch, if equipped.
• On models with compact master cylinder, remove proportioner valve assembly,Fig. .
• Depress primary piston and remove lock ring.
• Plug primary fluid ou...

BLEEDING BRAKES

Manual Bleeding

Pressure bleeding is recommended for all hydraulic systems. However, if a pressure bleeder is unavailable, use the following procedure.Brake fluid damages painted surfaces. Immediately clean any spilled fluid.

• Remove vacuum reserve by pumping brakes several times with engine off.
• Fill master cylinder reservoir with clean brake fluid. Check fluid level often during bleeding procedure; do not let reservoir fall below half full.
• If necessary, bleed master cylinder as follows:
• Disconnect master cylinder forward brake line connection until fluid flows from re...

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...

Should it become necessary to remove the caliper for installation of new parts, clean all parts in alcohol, wipe dry using lint free cloths, using an air hose to blow out drilled passages and bores. Check dust boots for punctures or tears. If punctures or tears are evident, new boots should be installed upon reassembly.

Inspect piston bores for scoring or pitting. Bores that show light scratches or corrosion can usually be cleaned with crocus cloth. However, bores that have deep scratches or scoring may be honed, provided the diameter of the...

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...