1995 GMC Safari Brake Service (ONLINE REPAIR MANUALS)

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 (...

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, Fig. , push piston back into its bore.
• Remove two mounting bolts and lift caliper away from disc.

Inspection

Should it become necessary to remove the caliper for installation of new parts, clean all parts in denatured alcohol, wipe dry using lint-free cloths. Using compressed air, blow out drilled passages and holes. Check dust boots for punctures or t...

Height Sensing Proportioning Valve

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 freely.
• Remove lever retaining nut and disconnect lever from valve shaft, Fig. .
• Rotate valve shaft to permit installation of correct adjustment gauge, Fig. , ensuring that D shape...

1992

The Rear Wheel Anti-Lock (RWAL) system, Fig. , reduces the occurrence of rear wheel lockup during severe braking by regulating rear hydraulic line pressure. Pressure applied to the rear wheel brakes is regulated by a control valve assembly located under the master cylinder. The control valve consists of a dump valve which releases hydraulic pressure into an accumulator, and an isolation valve which holds rear brake pressure. Operation of the dump valve and isolation valve is controlled by an Electronic Control Unit (ECU) which is mounted next to the master cylinder.

The ECU rec...

Except S & T Series w/VCM & VCM-A

This braking system, Figs. through , is designed to reduce the occurrence of wheel lock-up during severe braking conditions. To accomplish this function, the system regulates hydraulic brake line pressure by using an Electro-Hydraulic Control Unit (EHCU) module or a Brake Pressure Modulator Valve (BPMV). The EHCU/BPMV module has two types of valves: isolation valves, which maintain separate pressure for each front wheel and combine pressure for the rear wheels, and dump valves, which "dump" pressure to each front wheel separately and rear wheels comb...

The Bendix single piston sliding caliper disc brake is standard equipment on some truck applications, while on other trucks it is used only in Hydro-Boost power brake applications with both front disc brakes and 4 wheel disc brakes. On 4 wheel disc brakes, the front and rear systems are identical.

T...