Hummer H1 (2006+). Manual - part 232

7-10

Brake System

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Booster Functional Test

With the engine off, apply the brake pedal several times until the accumulator is completely depleted. Depress the brake pedal us-
ing 40 lb-ft (54 N•m) of force and start the engine. The pedal will fall and then push back against your foot. 

Accumulator Leakdown Test

1.

Start the engine and charge the accumulator by applying the brake pedal or by turning the steering wheel from stop to stop. 
Turn off the engine and let the vehicle sit for one hour. After one hour there should be at least two power-assisted applications
with the engine off.

2.

If the reserve system will not retain a charge for one hour, but functions normally immediately following charging, the
accumulator valves are at fault. Replace the hydro-booster.

3.

If the accumulator can be heard charging and discharging but does not hold a charge, replace the hydro-booster. 

4.

Deplete the accumulator by pressing the brake pedal several times. If the accumulator can has lost its charge, it is possible to
rotate or wobble the accumulator can with respect to the housing. Replace the hydro-booster. 

Handling - The booster should not be carried by the accumulator nor should the booster ever be dropped on the accumulator. The
snap ring which holds the accumulator into the housing should be checked for proper positioning before the booster is used. The
accumulator contains high pressure gas and with any high pressure gas a certain degree of danger is present if mishandled.

Disposal - The accumulator should not be exposed to excessive heat, fire or incineration. Before discarding accumulator following
replacement, drill a 1/16 inch diameter hole in the end of accumulator can to relieve the pressure. BE SAFE! Protect your eyes.
Wear approved safety glasses.

SERVICE BRAKE SYSTEM BLEEDING 

NOTE: If only the front or rear half of the system has been serviced, it is usually necessary to bleed only that half of the system.
However, if a firm brake pedal cannot be obtained after bleeding, it will be necessary to bleed the entire system. The brake hydrau-
lic system can be bled manually or by using a pressure tank and adapters. Each method is outlined in the following procedures.

WARNING:  Disconnect the batteries before bleeding the brake system. If the ABS modulator receives power during
the bleed procedure, air may become trapped in areas in the modulator that cannot be bled by conventional tech-
niques. The modulator would need to be replaced to obtain a firm brake pedal.

WARNING:  If the reservoir has run very low or dry, bleed the master cylinder before bleeding the remainder of the
brake system to keep from introducing additional air into the system.

WARNING:  Always wear eye protection when bleeding brakes. Failure to do this may cause injury if brake fluid
comes in contact with eyes.

Pressure Bleeding 

CAUTION:  When using a pressure bleeding tank J–29532, follow the manufacturer's instructions for its use. Use only DOT 3
brake fluids when bleeding. Do not exceed the recommended working pressure when pressurizing the tank. A tank pressure of 15-
20 psi (103-138 kPa) is sufficient to bleed the brake hydraulic system. Release all air pressure from the tank after using it.

NOTE: This procedure covers bleeding at one wheel. Repeat bleeding task for remaining wheels.

1.

Disconnect the batteries.

2.

Remove the cap from the master cylinder. Fill the master cylinder if necessary. 

3.

Install the pressure tank bleeder adapter to the master cylinder  (Figure  7-4).

4.

Connect the line from the pressure tank to the adapter.

NOTE: Bleed the calipers in the following order: right rear, left rear, right front, left front.

5.

Remove the protective cap from the bleeder screw on the caliper assembly  (Figure  7-5).

6.

Connect the short piece of hose to the bleeder screw, and place the other end of the hose in a container 3/4 full of brake fluid.

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7.

Open the valve on the line from the pressure tank to the master cylinder allowing the pressurized brake fluid to enter the
system
 (Figure  7-4).

8.

Open the bleeder screw 3/4 turn and observe the brake fluid in the container. Close the bleeder screw when the brake fluid
flows free of air bubbles  (Figure  7-5).

9.

Disconnect the hose from the bleeder screw and install the protective cap on the bleeder screw.

10. Close the valve on the line from the pressure tank to the master cylinder  (Figure  7-4).

11. Disconnect the line from the adapter.

12. Remove the adapter from the master cylinder and fill the master cylinder if necessary.

13. Install the master cylinder cap. 

14. Connect the batteries.

Figure 7-4:   Pressure Bleeding Brake System

Manual Bleeding 

NOTE: This procedure covers bleeding at one wheel. Repeat the bleeding task for remaining wheels. Assistance is required to de-
press the brake pedal when manually bleeding brakes while the tech opens and closes bleeder screw.

NOTE: Bleed the calipers in the following order: right rear, left rear, right front, left front.

1.

Disconnect the batteries.

2.

Remove the protective cap from the bleeder screw on the caliper assembly  (Figure  7-5).

3.

Connect the short piece of hose to the bleeder screw, and place the other end of the hose in a container 3/4 full of brake fluid.

CAUTION: Check the master cylinder fluid level frequently during the bleeding operation and refill the reservoirs as necessary.
Do not allow the master cylinder to run out of fluid at any time, or additional air will be drawn into the system.

4.

Have an assistant depress the brake pedal. Open the bleeder screw 3/4 turn.

PRESSURE TANK BLEEDER ADAPTER

MASTER CYLINDER

VALVE

PRESSURE TANK

7-12

Brake System

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Figure 7-5:   Manually Bleeding Brake System

5.

When the pedal reaches the floor, tighten the bleeder screw and have your assistant slowly release the brake pedal.

6.

Repeat steps 3 and 4 until the fluid flows clear and free of air bubbles.

7.

Disconnect the hose from the bleeder screw and install the protective cap on the bleeder screw.

8.

Connect the batteries.

9.

Operate the vehicle and check the brakes for proper operation.

SERVICE BRAKE PAD REPLACEMENT

NOTE: The following procedure applies to the front brake system only.

Removal

1.

Using a crowfoot, remove the two capscrews and washers securing the yoke and the caliper to the adapter.

NOTE: Note the positioning of the brake pad surfaces for installation.

2.

Remove the yoke, caliper, and two brake pads.

Cleaning and Inspection 

NOTE: Clean all the components, examine for wear or damage, and replace if necessary.

1.

Inspect the dust boot for tears or deterioration (Figure  7-6).

2.

Inspect the rotor for heat cracks, spotting, discoloration, pitting, or scoring. Resurface the rotors if discolored, pitted, or scored.
It is not recommended that the rotors be turned when spotted or heat cracks. 

3.

Inspect the brake pads for glazing, oil saturation, or wear. If glazed, oil saturated, or if brake lining thickness is less than 1/8 in.
(3.2 mm), replace the brake pads. The brake pads should be replaced as an axle set (front or rear).

Installation

1.

Check the brake pad backing plate notches for burrs or excess coating and ensure that the pad will fit the adapter slide with 
enough clearance to afford stick-free movement.

2.

Lubricate the caliper guide pins, sleeves and adapter slides with Permatex

®

Ultra Disc Brake Caliper Lube prior to installation.

BLEEDER SCREW

PROTECTIVE

CAP

HOSE

CALIPER

ASSEMBLY

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WARNING:  Ensure the brake pads are installed with linings facing rotor. Failure to do this will cause poor performance,
damage to equipment, and may result in injury.

3.

Position the brake pads on the adapter.

NOTE: When installing the yoke and the caliper, use a suitable tool to compress the piston.

4.

Apply a non-hardening thread-locking compound to the tapped holes of the adapter. Using the crowsfoot, secure the yoke and
caliper to the adapter with the two washers and capscrews. Tighten the capscrews to 30-40 lb-ft (41-54 N•m).

LINING AND ROTOR BURNISHING

After you replace the brake pads and/or refinish the rotors, it is recommended that the new braking surface be broken in, or “bur-
nished.” To do this, make 20 stops, one every one to two miles at 30 mph, using medium pedal effort. The amount of time it takes
to stop should be approximately five seconds. During this procedure, use care to avoid overheating the brakes.

Figure 7-6:   Caliper Assembly

FRONT SERVICE BRAKE CALIPER REPLACEMENT

NOTE: The following procedure applies to the front brake system only. If removing the left front caliper, the halfshaft must be re-
moved.

Removal

1.

Disconnect the brake line from the coupling (Figure  7-7).

2.

Using a crowfoot, remove the two capscrews and washers securing the yoke and the caliper to the adapter.

NOTE: Note the positioning of the brake pad surfaces for installation.

3.

Remove the yoke, caliper, and the two brake pads from the adapter.

4.

Slide the yoke and caliper guide pins out from the caliper. Remove the coupling and washer from the caliper.

Cleaning and Inspection 

NOTE: Clean all the components, examine for wear or damage, and replace if necessary.

1.

Clean the mating surfaces of the caliper and adapter  (Figure  7-7).

2.

Inspect the caliper and caliper piston for pitting, or damage  (Figure  7-6).

3.

Inspect the caliper guide pins and sleeves for wear.

4.

Inspect the dust boot and bushings for tears or deterioration.

5.

Inspect the yoke and caliper guide pins for corrosion. Perform step 6 if corroded. If not, perform step 8 (Figure  7-7).

6.

Remove the caliper guide pins from the yoke. Discard the caliper guide pins.

7.

Inspect the rotor for heat checks, discoloration, pitting, or scoring. Check the rotor thickness variation.

CALIPER

PISTON

DUST BOOT