1991 Chevrolet S10 Pickup Brake Service (ONLINE REPAIR MANUALS)

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. ...

DESCRIPTION

Hydro-Boost II is an hydraulically operated power brake booster. The hydraulic brake booster consists of an open center spool valve and an hydraulic cylinder combined into a single housing. The power steering pump provides the hydraulic fluid pressure to operate both the power brake booster and the power steering gear.

A dual master cylinder is bolted to the brake booster and is operated by a pushrod projecting from the booster cylinder bore.

The Hydro-Boost II also has an accumulator system which stores sufficient fluid under pressure to provide one power assisted brake...

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...

This braking system Fig. 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 Electronic Hydraulic Control Unit (EHCU) module. This control module has two types of valves. Isolation valves which maintain pressure to each front wheel separately and rear wheels combined. Dump valves which dump pressure to each front wheel separately and rear wheels combined. These valves are controlled by a microcomputer which is part of the EHCU module. During a severe brak...

WIRING DIAGRAMS

Refer to "Wiring Diagrams" in "Vehicle Systems."

READING TROUBLE CODES

Trouble codes are accessed by connecting a jumper wire between terminals A and H of the underdash ALDL connector and observing the flashes of the brake warning lamp. Note the following when performing the Diagnostic Circuit Check to access trouble codes.

• When the terminals are jumped, count the number of short flashes starting from the initial long flash and including the long flash in the count.
• The count sequence will repeat as long as the ALDL connector terminals are jumped with the ignition on.
• ...

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 free (no load condition).
• Remove lever retaining nut and disconnect lever from valve shaft, Fig. .
• Rotate valve shaft to permit installation of correct adjustment gauge, Fig. ,...