Content .. 788 789 790 791 ..

Hummer H2. Manual - part 790

15. Select a smooth, dry, clean and level road that is as free of heavy traffic as possible for brake system

moderate speed road testing.

16. Drive the vehicle at a moderate speed. Observe for a pull and/or incorrect tracking of the vehicle without

the brakes applied.

17. While continuing to drive the vehicle at a moderate speed, perform several light applies of the brakes.

Observe the pedal effort and the pedal travel, observe for brake system noise, pulsation and/or brake drag.

18. If the brake pedal apply effort was excessive, or the pedal travel was excessive. DO NOT continue to test

drive the vehicle until it is repaired.

19. If the brake pedal apply effort was not excessive and the pedal travel was not excessive, proceed to next

step.

20. While continuing to drive the vehicle at a moderate speed, perform several moderate applies of the

brakes. Observe the pedal effort and the pedal travel, observe for brake system pulsation and/or uneven
braking action, either side to side, or front to rear. A small amount of vehicle front end dip is expected
during a moderate apply of the brakes.

21. If the brake pedal apply effort was excessive, or the pedal travel was excessive. DO NOT continue to test

drive the vehicle until it is repaired.

BRAKE SYSTEM INTERNAL LEAK TEST

1. Start the engine and allow it to idle.

2. Apply light, steady pressure to the brake pedal. Observe both the brake pedal feel and travel.

3. Release the brakes and turn OFF the ignition.

4. If the brake pedal apply felt spongy, but the brake pedal travel was not excessive, perform the following

steps:

Inspect the brake system for external leaks. See BRAKE SYSTEM EXTERNAL LEAK
INSPECTION under ADJUSTMENTS & INSPECTION.

Pressure bleed the brake system in order to purge any air that may be trapped in the system. See
MANUAL BLEEDING or PRESSURE BLEEDING under BLEEDING BRAKE SYSTEM.

5. If the brake pedal apply did not feel spongy, but the brake pedal travel was excessive, loosen the master

cylinder-to-brake power booster mounting nuts. Carefully pull the master cylinder away from the brake
power booster just enough to inspect the mounting surface of the master cylinder. Inspect the master
cylinder mounting surface at the primary piston for brake fluid leaks. See Fig. 12 .

WARNING:

Brake fluid may irritate eyes and skin. In case of eye contact, rinse
thoroughly with water. In case of skin contact, wash with soap and water.
In case of ingestion, consult a physician immediately.

CAUTION: Avoid spilling brake fluid onto painted surfaces, electrical connections,

wiring, or cables. Brake fluid will damage painted surfaces and cause
corrosion to electrical components. If any brake fluid comes in contact
with painted surfaces, immediately flush the area with water. If any brake
fluid comes in contact with electrical connections, wiring, or cables, use a
clean shop cloth to wipe away the fluid.

2004 Hummer H2

2003-04 BRAKES Disc - Hummer

6. If the master cylinder exhibits any leakage around the primary piston, then the primary piston primary

seal and/or secondary seal is leaking and the master cylinder requires overhaul or replacement:

For overhaul, see MASTER CYLINDER under OVERHAUL.

For replacement, see MASTER CYLINDER under REMOVAL & INSTALLATION.

7. If the master cylinder primary piston does not exhibit any leakage, pressure bleed the brake system. See

MANUAL BLEEDING or PRESSURE BLEEDING under BLEEDING BRAKE SYSTEM.

8. If the brake pedal apply did not feel spongy, and the brake pedal travel was initially steady and not

excessive, but then gradually fell, then the master cylinder requires overhaul or replacement due to an
internal leak past the secondary piston from the secondary piston primary seal or secondary seal.

9. If the brake pedal apply did not feel spongy, and the brake pedal travel was initially steady and not

excessive, then fell slightly, then became steady again, then the Brake Pressure Modulator Valve (BPMV)
may be leaking internally, and may require replacement. See appropriate ANTI-LOCK BRAKES article.

Fig. 12: Inspecting Master Cylinder For Fluid Leaks
Courtesy of GENERAL MOTORS CORP.

SERVICING

BURNISHING PADS & ROTORS

CAUTION: Road test a vehicle under safe conditions and while obeying all traffic

laws. Do not attempt any maneuvers that could jeopardize vehicle control.

2004 Hummer H2

2003-04 BRAKES Disc - Hummer

Burnishing the brake pads and brake rotors is necessary in order to ensure that the braking surfaces are properly
prepared after service has been performed on the disc brake system. This procedure should be performed
whenever the disc brake rotors have been refinished or replaced, and/or whenever the disc brake pads have been
replaced.

1. Select a smooth road with little or no traffic.

2. Accelerate the vehicle to 30 Mph (48 Km/h).

Using moderate to firm pressure, apply the brakes to bring the vehicle to a stop. DO NOT allow the
brakes to lock.

4. Repeat until approximately 20 stops have been completed. Allow sufficient cooling periods between

stops in order to properly burnish the brake pads and rotors.

REMOVAL & INSTALLATION

BRAKE BOOSTER

Removal & Installation

1. Apply the park brake and block the wheels. Disconnect the inlet hose, the steering gear hose, and the

return hoses from the booster assembly. Remove the master cylinder retaining nuts and remove the master

Failure to adhere to these precautions could lead to serious personal
injury and vehicle damage.

CAUTION: Use care to avoid overheating the brakes while performing this next

step.

CAUTION: Use the correct fastener in the correct location. Replacement fasteners

must be the correct part number for that application. Fasteners requiring
replacement or fasteners requiring the use of thread locking compound or
sealant are identified in the service procedure. DO NOT use paints,
lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces
unless specified. These coatings affect fastener torque and joint clamping
force and may damage the fastener. Use the correct tightening sequence
and specifications when installing fasteners in order to avoid damage to
parts and systems.

NOTE:

Avoid spilling brake fluid onto painted surfaces, electrical connections, wiring,
or cables. Brake fluid will damage painted surfaces and cause corrosion to
electrical components. If any brake fluid comes in contact with painted
surfaces, immediately flush the area with water. If any brake fluid comes in
contact with electrical connections, wiring, or cables, use a clean shop cloth to
wipe away the fluid.

2004 Hummer H2

2003-04 BRAKES Disc - Hummer

cylinder. DO NOT disconnect the brake pipes.

2. Remove the stop lamp switch retaining clip from the brake pedal pin. See Fig. 13 . Remove the stop light

switch and the pushrod from the brake pedal pin. Remove the booster to bulkhead nuts. Remove the
booster assembly. Remove the gasket.

3. Install the gasket. Install the booster assembly.

4. Install the booster to bulkhead nuts. Tighten the nuts to specification. See TORQUE

SPECIFICATIONS . Install the stop lamp switch and the pushrod to the brake pedal pin. Install the stop
lamp switch retaining clip to the brake pedal pin.

5. Install the master cylinder and the master cylinder retaining nuts. Tighten the nuts to specification.

Connect the return hose, the steering gear hose, and the inlet hoses.

6. Bleed the hydraulic brake booster system. See POWER RACK & PINION article in STEERING. Release

the park brake and unblock the wheels.

Fig. 13: Removing/Installing Hydraulic Brake Booster
Courtesy of GENERAL MOTORS CORP.

BRAKE CALIPER

2004 Hummer H2

2003-04 BRAKES Disc - Hummer

Content .. 788 789 790 791 ..