1992 Buick Lesabre Brake Service (ONLINE REPAIR MANUALS)

MASTER CYLINDER OVERHAUL

EXCEPT CORVETTE

Disassemble

Refer to Figs. and when performing the following procedures.

• 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 fl...

AC-DELCO TANDEM DIAPHRAGM TYPE

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.

AC-DELCO SINGLE DIAPHRAGM TYPE

The AC-Delco power booster assembly, Fig. is located along the bulkhead in ...

When troubleshooting the hydraulic brake system, perform the following checks and inspections as outlined below. If problem still exists within system, refer to Fig. first, then to Figs. and as necessary.

CHECKING FOR FLUID LEAKAGE

Start engine and depress the brake pedal. If the pedal gradually falls under constant pressure, the hydraulic system may be leaking. Raise the vehicle on a lift and check all tubing lines and backing plates for signs of leakage. It may be necessary to lift or re...

Refer to Fig. , for overview of anti-lock brake system.

The purpose of the anti-lock brake system is to prevent wheel lock-up under heavy braking conditions, on virtually any road surface. When a wheel locking condition exists, the pressure modulator valve (PMV) assembly isolates each wheel hydraulic circuit, then begins modulation of fluid pressure to each wheel according to wheel speed input to the EBCM. The PMV is controlled by the Electronic Brake Control Module (EBCM).

Modulation occurs by means of three ABS modes: pressure hold, pressure reduce and pressure increase. The PMV ass...

BRAKE PEDAL

Toyota/GM Single Diaphragm Type

• With engine running and brake pedal in rest position, measure distance between face of pedal and floor mat.
• If distance is not 5.79-6.18 inches, adjust pedal height as follows:
• Remove left lower instrument panel trim section and air duct.
• Loosen stop lamp switch sufficiently to gain clearance for pedal adjustment.
• Loosen locknut and rotate pedal pushrod as needed to obtain specified pedal height, then tighten locknut.
• Adjust position of brake light switch so that plunger lightly contacts pedal stopper and brake lamps are off when pedal is release...

REMOVAL

• Remove caliper assembly as described in "Caliper Service."
• Remove shoe and lining assemblies from caliper, Figs. through , noting the following:
• On models with tab mount outer shoe (all except series 3264), straighten bent over shoe tabs with suitable pliers.
• On models with spring mount outer shoe (series 3264), insert screwdriver between shoe and caliper and disengage buttons on shoe from holes in caliper.
• Remove sleeves and bushings from grooves in caliper mounting bolt holes, Figs. through .

INSTALLATION

• Lubricate new bushings with suitable grease, install bushings in cali...