Chevrolet Silverado / GMC Sierra. Service manual — part 2389

Cloudy appearance - moisture

Dark appearance/suspended particles in fluid - dirt, rust, corrosion, brake dust

2. Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder

grommets for swelling, indicating brake fluid contamination.

3. If the brake fluid WAS contaminated with an oil-based or a silicone-based substance,

indicated by fluid separation and/or a swollen master cylinder reservoir cap diaphragm
and/or swollen reservoir-to-master cylinder grommets, perform the following:

1. Remove ALL of the following components listed from the vehicle. Each component

contains internal rubber seals/linings which have been contaminated by the
contaminated brake fluid in the brake hydraulic system.

Refer to the procedures indicated:

Master Cylinder Replacement (JD9, JF3, JF7)Master Cylinder
Replacement (JH6, JH7)

Front Brake Hose Replacement (JD9, JF3, JF7)Front Brake Hose
Replacement (JH6, JH7)

Rear Brake Hose Replacement (Frame to Axle - JH6, JH7)Rear Brake
Hose Replacement (Frame to Axle - JD9, JF3 w/JL4)Rear Brake Hose
Replacement (Caliper - JH6, JH7)Rear Brake Hose Replacement (Caliper
- JD9)Rear Brake Hose Replacement (Frame to Axle - JF3 w/o JL4, JF7)

Front Brake Caliper Replacement (JH6, JH7) Front Brake Caliper
Replacement (JD9, JF3, JF7)

Rear Brake Caliper Replacement (JH6, JH7) Rear Brake Caliper
Replacement (JD9)

Brake Pressure Modulator Valve Replacement (JD9, JF3, JF7) Brake
Pressure Modulator Valve Replacement (JH6, JH7)

2. Clean out all the hydraulic brake pipes using denatured alcohol, or equivalent.

3. Dry the brake pipes using non-lubricated, filtered air.

4. Repair or replace ALL of the following components listed and install them to the

vehicle. Each component contains internal rubber seals/linings which have been
contaminated by the contaminated brake fluid in the brake hydraulic system.

Refer to the procedures indicated:

Master Cylinder Replacement (JD9, JF3, JF7)Master Cylinder
Replacement (JH6, JH7) ; also perform the following:

2008 Chevrolet Silverado 1500

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

Clean the brake master cylinder reservoir using denatured alcohol, or equivalent,
then dry the reservoir using non-lubricated, filtered air. Inspect the reservoir for
cracks and/or damage and replace if necessary. Refer to Master Cylinder
Reservoir Replacement (JD9, JF3, JF7)Master Cylinder Reservoir
Replacement (JH6, JH7) .

Replace the brake master cylinder reservoir cap diaphragm.

Front Brake Hose Replacement (JD9, JF3, JF7)Front Brake Hose
Replacement (JH6, JH7)

Rear Brake Hose Replacement (Frame to Axle - JH6, JH7)Rear Brake
Hose Replacement (Frame to Axle - JD9, JF3 w/JL4)Rear Brake Hose
Replacement (Caliper - JH6, JH7)Rear Brake Hose Replacement (Caliper
- JD9)Rear Brake Hose Replacement (Frame to Axle - JF3 w/o JL4, JF7)

Front Brake Caliper Overhaul (JH6, JH7) or Front Brake Caliper
Replacement (JH6, JH7) Front Brake Caliper Replacement (JD9, JF3,
JF7)

Rear Brake Caliper Overhaul (JH6, JH7) or Rear Brake Caliper
Replacement (JH6, JH7) Rear Brake Caliper Replacement (JD9)

Brake Pressure Modulator Valve Replacement (JD9, JF3, JF7) Brake
Pressure Modulator Valve Replacement (JH6, JH7)

4. If the brake fluid was NOT contaminated with an oil-based or a silicone-based substance,

but WAS contaminated with water or dirt, rust, corrosion, and/or brake dust, replace the
brake master cylinder reservoir cap diaphragm. The diaphragm may have allowed the
moisture or particles to enter the hydraulic system.

5. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11®,

GM P/N 12377967 (Canada P/N 992667) or equivalent, DOT-3 brake fluid from a clean,
sealed brake fluid container.

6. Pressure bleed the hydraulic brake system. Begin the procedure with the pressure bleeder

reservoir filled to the maximum-fill level with the correct brake fluid as indicated. Refer to
Hydraulic Brake System Bleeding (Pressure) or Hydraulic Brake System Bleeding
(Manual).

POWER VACUUM BRAKE BOOSTER REPLACEMENT (NON-ADJUSTABLE PEDALS)

2008 Chevrolet Silverado 1500

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

Fig. 33: Power Vacuum Brake Booster Replacement (Non-Adjustable Pedals)
Courtesy of GENERAL MOTORS CORP.

Callout

Component Name

Preliminary Procedures

1. Apply the park brake.

2. Deplete the vacuum reserve in the vacuum booster by applying the brake pedal 3 times

or until the pedal becomes firm.

1

Brake Booster Pushrod Retainer Bolt

Tighten: 10 N.m (89 lb in)

NOTE:

Refer to Fastener Notice .

2

Brake Booster Pushrod Retainer

3

Stop Lamp Switch

4

Brake Booster Pushrod

Brake Booster Nut (Qty: 4)

2008 Chevrolet Silverado 1500

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

POWER VACUUM BRAKE BOOSTER REPLACEMENT (ADJUSTABLE PEDALS)

5

Tip: Tighten the upper right vacuum brake booster nut first.

Tighten: 33 N.m (24 lb ft)

6

Master Cylinder Nut (Qty: 2)

Tighten: 33 N.m (24 lb ft)

7

Master Cylinder Assembly

Procedure

1. Without disconnecting the brake pipe fittings, carefully position the master

cylinder assembly aside and support with heavy mechanics wire or
equivalent.

2. Inspect the brake master cylinder to vacuum brake booster seal for damage

and replace if necessary.

3. Ensure the brake master cylinder to vacuum brake booster seal is properly

seated in the groove of the master cylinder.

8

Vacuum Brake Booster Hose Clamp

9

Vacuum Brake Booster Hose

10

Vacuum Brake Booster

Procedure

1. Disconnect the vacuum brake booster electrical connectors, if equipped.

2. Discard the vacuum brake booster gasket.

3. Install a new vacuum brake booster gasket.

2008 Chevrolet Silverado 1500

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