1991 GMC K1500 Pickup Brake Service (ONLINE REPAIR MANUALS)

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. Gr...

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...

BLEEDING BRAKES

Manual Bleeding

• If vehicle is equipped with power brakes, remove vacuum reserve by applying brakes several times with engine off.
• Fill master cylinder reservoirs with suitable brake fluid. Be sure to always keep master cylinder reservoirs at least half full during entire bleeding procedure.
• If master cylinder is suspected to have air in the bore, it must be bled first, as follows:
• Disconnect forward brake pipe connection at master cylinder.
• Allow brake fluid to fill master cylinder bore until it begins to flow from forward pipe connector port.
• Connect and tighten forward...

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 receives ...

DESCRIPTION

These units, Figs. and , have a vacuum power chamber that consists of a front and rear shell, a housing divider, front and rear diaphragm and plate assemblies, an hydraulic pushrod and a diaphragm return spring.

The unit operates in much the same manner as the Single Diaphragm unit described above. The diaphragm and plate assemblies use the pressure differential created by engine intake manifold vacuum and atmospheric pressure to assist the hydraulic pushrod.

BOOSTER SERVICE

Disassemble

• Remove boot, silencer, vacuum check valve, grommet and front housing seal Fig. ...

DELCO MORAINE TYPE

COMPOSITE TYPE

Refer to Figs. and when performing the following procedures.

Disassemble

• Remove master cylinder from vehicle.
• 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 and proportioner valve assembly, if equipped.
• Depress primary piston and remove lock ring.
• Plug primary fluid outlet (outlet nearest to cowl when master cylinder is installed), then apply compressed air into secondary fluid outlet to remove primary and secondary pistons.
• R...