1994 GMC Safari Brake Service (ONLINE REPAIR MANUALS)

Certain general service procedures apply, regardless of whether the brakes are vacuum or hydraulically assisted. Only top quality, clean brake fluid should be used. More seals and valves are used with power brake systems than with ordinary brakes, so an inferior brake fluid will do much more damage. For the same reason, be sure all dirt is kept out of the system. Additionally, care must be taken not to mix the fluids of the booster hydraulic system and brake hydraulic system as the fluids are not compatible.

If the power unit fails, the brakes will still operate, as the conventio...

The braking system can be bled manually or with pressure bleeding equipment. If bleeding manually, check fluid level frequently.

Brake fluid should never be reused. Before driving the vehicle, check brake operation to ensure a firm pedal has been obtained.

Brake fluid will damage electrical connections and painted surfaces. Use shop cloths, suitable containers, and fender covers to prevent brake fluid from contacting these areas. Always seal and wipe off brake fluid containers to prevent spills.

Manual Bleeding

C/K, G, M/L, P & S/T Series

• If vehicle is equipped with a vacuum or hy...

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...

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...

Brake System Bleed

1992-95

Electro-Hydraulic Control Unit Brake Pressure Modulator Valve (EHCU/BPMV) Module

The EHCU/BPMV Module should be bled after replacement or if air is trapped in the unit. If bleeding is required, the module must be bled thoroughly before the wheel cylinders and calipers.

There are two bleeders on top of the unit that appear to be normal bleeders, Fig. . These are modulator bleeders and must remain closed when the unit is not pressurized.

The internal bleeders are on either side of EHCU/BPMV module. The valves are used to open the internal passages within the E...

Duo-Servo Brakes

Removal

• Raise and support vehicle, then remove tire and wheel assembly.
• Remove brake drum. If brake lining is dragging on brake drum, back off brake adjustment by rotating adjustment screw. Refer to individual truck chapter for procedure. If brake drum is rusted or corroded to axle flange and cannot be removed, lightly tap flange to drum mounting surface with a suitable hammer.
• Using brake spring pliers or equivalent, unhook primary and secondary return springs, Fig. . Observe location of brake parts being removed to aid during installation.
• Remove brake hold-down spri...