Chevrolet Silverado / GMC Sierra. Service manual — part 2396

steering pump (8).

BRAKE ASSIST SYSTEM DESCRIPTION AND OPERATION (VACUUM ASSIST)

System Component Description

The brake assist system consists of the following:

Brake Pedal

Receives, multiplies and transfers brake system input force from driver.

Brake Pedal Pushrod

Transfers multiplied input force received from brake pedal to brake booster.

Vacuum Brake Booster

Uses source vacuum to decrease effort required by driver when applying brake system input
force.
When brake system input force is applied, air at atmospheric pressure is admitted to the rear
of both vacuum diaphragms, providing a decrease in brake pedal effort required. When
input force is removed, vacuum replaces atmospheric pressure within the booster.

Vacuum Source

Supplies force used by vacuum brake booster to decrease brake pedal effort.

Vacuum Source Delivery System

Enables delivery and retention of source vacuum for vacuum brake booster.

System Operation

Brake system input force is multiplied by the brake pedal and transferred by the pedal pushrod to
the hydraulic brake master cylinder. Effort required to apply the brake system is reduced by the
vacuum brake booster.

Active Brake Booster

Incorporated into the vacuum brake booster, is an electric solenoid actuator. This actuator can be
used to apply the brake booster and thus the master cylinder as commanded by the electronic
brake control module (EBCM). During stability events, the EBCM can command the solenoid

2008 Chevrolet Silverado 1500

2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

actuator in the brake booster to apply the booster. This quickly provides a large volume of
pressurized brake fluid to the brake pressure modulator valve (BPMV). The BPMV will then
control the flow of fluid to the brake corners to obtain the appropriate response for the vehicle.

SPECIAL TOOLS AND EQUIPMENT

SPECIAL TOOLS

Illustrations

Tool Number/Description

J 26889

Accumulator Piston Compressor

J 28662

Brake Pedal Effort Gauge

J 29532

Diaphragm Pressure Bleeder

2008 Chevrolet Silverado 1500

2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

J 35589-A

Brake Pressure Bleeder Adapter

J 45405

Brake Pipe Flaring Tool

2008 Chevrolet Silverado 1500

2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

2008 ACCESSORIES & EQUIPMENT

Instrument Panel and Console Trim - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra

& Silverado

SPECIFICATIONS

FASTENER TIGHTENING SPECIFICATIONS

Application

Specification

Metric

English

Front Floor Console Armrest Screws

2 N.m

18 lb in

Front Floor Console Compartment Screws

2 N.m

18 lb in

Front Floor Console Cupholder Screws

2 N.m

18 lb in

Front Floor Console End Panel Screws

2 N.m

18 lb in

Front Floor Console Inner Cover Screws

2 N.m

18 lb in

Front Floor Console Latch Inner Screws

2 N.m

18 lb in

Front Floor Console Latch Outer Screws

2 N.m

18 lb in

Instrument Panel Accessory Switch Screws

2 N.m

18 lb in

Instrument Panel Carrier Bolts

9 N.m

80 lb in

Instrument Panel Carrier Support Bolts

22 N.m

16 lb ft

Instrument Panel Carrier Support Lower Bolt
(w/RPO SLT)

2 N.m

18 lb in

Instrument Panel Cluster Screws

2 N.m

18 lb in

Instrument Panel Center Support Bracket Bolt

22 N.m

16 lb ft

Instrument Panel Cluster Trim Panel Screws
(w/RPO SLT)

2 N.m

18 lb in

Instrument Panel Cluster Trim Plate Cover Screws

2 N.m

18 lb in

Instrument Panel Compartment Screws

2 N.m

18 lb in

Instrument Panel Compartment Latch Screws

2 N.m

18 lb in

Instrument Panel Compartment Door Screws
(w/RPO SLT)

2 N.m

18 lb in

Instrument Panel Compartment Striker Screws

2 N.m

18 lb in

Instrument Panel Insulator Screws

2 N.m

18 lb in

Instrument Panel Knee Bolster Deflector Nuts

9 N.m

80 lb in

Instrument Panel Knee Bolster Screws

2 N.m

18 lb in

Instrument Panel Lower Trim Panel Screws

2 N.m

18 lb in

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Instrument Panel and Console Trim - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Instrument Panel and Console Trim - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado