Hummer H1 (2006+). Manual - part 233

7-14

Brake System

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NOTE: Replace the brake pads in sets only. Replace the brake pads if the brake lining thickness is less than 1/8 in. (3.2 mm) and
operation in wet and muddy conditions is expected.

8.

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 both of the pads and the pads from the opposite caliper. 

Installation

1.

Install a washer and coupling to the caliper  (Figure  7-6).

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

2.

Position the brake pads on the adapter  (Figure  7-7).

Figure 7-7:   Service Brake Components

3.

Inspect the caliper guide pins and replace if worn, pitted or corroded.

4.

Apply a medium strength thread-locking compound to the threads of caliper the guide pins and install the pins into the yoke (if
removed during cleaning and inspection). Tighten the caliper guide pins to 30 lb-ft (41 N•m).

5.

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

®

Ultra Disc Brake Caliper Lube prior to installation.

6.

Position the caliper onto the yoke. 

NOTE: When installing the calipers, use a suitable tool to bottom out the piston in the caliper if needed.

7.

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

8.

Connect the brake line to the coupling and bleed the brake system.

MASTER CYLINDER REPLACEMENT

Removal

CAUTION: Cover or plug all open connections immediately after disconnecting to prevent contamination

NOTE: Have a drainage container ready to catch the brake fluid.

ADAPTER

BRAKE PAD

YOKE

CALIPER

CALIPER

COUPLING

TAPPED HOLE

GUIDE PINS

BRAKE

LINE/HOSE

COPPER
WASHER

BRAKE PAD

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 Brake System  7-15

5745804

1.

Disconnect the front and rear brake lines from the master cylinder  (Figure  7-8).

CAUTION: Do not apply excessive pressure or force on the master cylinder.

2.

Remove the two locknuts and master cylinder from the hydro-boost. Discard the locknuts  (Figure  7-8).

Installation

1.

Bench-bleed the master cylinder.

Figure 7-8:   Master Cylinder 

2.

Install the master cylinder to the hydro-boost with two locknuts. Tighten the locknuts to 22 lb-ft (30 N•m) (Figure  7-8).

3.

Install the front and rear brake lines to the master cylinder. Position the front and rear brake lines with a minimum of 1/2"
clearance to the hydro-boost accumulator and the right rear modulator output line. Clearance between the front and rear lines is
also 1/2" minimum.

MASTER CYLINDER BLEEDING 

NOTE: The master cylinder must be filled and kept at least half full during the bleeding operation (Figure  7-9). 

1.

Depress the brake pedal slowly and hold. Loosen the front brake line to purge air from the front section of the reservoir.

2.

Tighten the front brake line and release the brake pedal.

3.

Repeat steps 1 and 2 until the front reservoir is purged of air.

4.

Repeat steps 1 through 3 for the rear reservoir with the rear brake line.

5.

Bleed the brake system.

MASTER CYLINDER BENCH BLEEDING

NOTE: The master cylinder must be filled and kept at least half full during the bleeding operation. Perform this procedure prior to
installing the master cylinder on the vehicle.

1.

Secure the master cylinder flange in a vise.

2.

Remove the cover and fill the reservoir with DOT 3 brake fluid.

3.

Screw the threaded end of the bleeder hose into the brake line port on the master cylinder and insert the opposite end into the
reservoir. Repeat this step for the other bleeder hose (Figure  7-9).

4.

Slowly push the piston into the master cylinder. Do not release the piston. Air will be forced into the hoses. Repeat as needed
until no bubbles are noted from the lines. The lines must stay in the fluid until installed. 

5.

Refill the reservoir with DOT 3 brake fluid and repeat step 4 until no air bubbles remain in the brake fluid.

HYDRO-BOOST

MASTER

CYLINDER

REAR

BRAKE

LINE

FRONT
BRAKE

LINE

RIGHT MASTER

CYLINDER

MOUNTING STUD

7-16

Brake System

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6.

Remove the bleeder hoses from the brake line ports on the master cylinder.

7.

Install the cap on the master cylinder and remove from the vise.

8.

Install the master cylinder.

9.

Bleed the brake system.

Figure 7-9:   Bench Bleeding Master Cylinder 

HYDRO-BOOST REPLACEMENT

Removal

1.

Remove the two nuts securing the splash shield mount bracket to the hydro-boost/master cylinder assembly.

2.

Remove the nut securing the mount bracket to the splash shield and remove the mount bracket.

3.

Remove the two nuts securing the master cylinder to the hydro-boost and pull the master cylinder out and to one side.

4.

Disconnect the two high pressure lines and one return line from the hydro-boost  (Figure  7-10).

5.

Remove the cotter pin, washer, and pushrod from the brake pedal bellcrank. Remove the spring washer from the brake pedal
bellcrank and discard the cotter pin and spring washer.

6.

Remove the four nuts, lockwashers, washers, gasket, and the hydro-boost from the cowl. Discard the lockwashers.

Installation

1.

Install the gasket and the hydro-boost on the cowl with four washers, lockwashers, and nuts. Do not tighten the nuts. (Figure
 7-10). 

2.

Install the spring washer on the brake pedal bellcrank. Connect the hydro-boost pushrod to the brake pedal bellcrank. Install
the washer and cotter pin.

3.

Tighten the nuts to 21 lb-ft (28 N•m).

4.

Connect the two high pressure lines and one return line to the hydro-boost.

5.

Install the master cylinder and the splash shield mount bracket.

6.

Bleed the hydro-boost system.

CAP

BLEEDER

VISE

PISTON

FLANGE

MASTER CYLINDER

HOSES

RESERVOIR

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 Brake System  7-17

5745804

BLEEDING THE HYDRO-BOOST SYSTEM

Whenever the booster is removed and installed, the steering system should be bled. 

1.

Fill the power steering pump reservoir to the proper level and let the fluid remain undisturbed for at least two minutes. 

2.

Start the engine and run momentarily. Add fluid if necessary. 

3.

Repeat steps 1 and 2 until the fluid level remains constant after running the engine. 

4.

Turn off the engine. 

5.

Raise the front of the vehicle so the wheels are off the ground. Support the vehicle with suitable safety stands. 

6.

Turn the wheels from stop to stop. Add fluid if necessary.

7.

Lower the vehicle from the safety stands. 

8.

Start the engine and depress the brake pedal several times while rotating the steering wheel from stop to stop. 

9.

Turn the engine off and pump the brake pedal 4 to 5 times.

CAUTION: The HUMMER H1 is equipped with DOT 3 brake fluid. Do not mix with other brake fluids. Failure to use the proper
brake fluid will damage the brake system.

10. Check the brake fluid level. Add fluid if necessary. 

11. If the fluid is extremely foamy, allow the vehicle to stand a few minutes with the engine on. Then repeat steps 7, 8, and 9.

12. Check for the presence of air in the oil. Air in the oil will give the fluid a milky appearance. Air in the system will also cause

the fluid level in the pump to rise when the engine is turned off. 

Figure 7-10:   Hydro-boost Replacement Procedure

BRAKE LINE REPLACEMENT

Metal brake lines should be inspected for leaks or deterioration every time the vehicle is being serviced.

WARNING:  The batteries must be disconnected when the brake hydraulic system is being serviced and bled. If the
ABS motor pump runs when air is in the hydraulic system, air can get trapped behind the valves in the modulator
causing a spongy brake pedal.

NOTE: After servicing the brake system, bleed the brakes and refill as necessary. 

Front Brake Line Replacement

NOTE: The procedure is the same for the right and left front brake lines.

1.

Disconnect the brake line from the caliper.

SPRING WASHER

BRAKE

PEDAL

BELLCRANK

COWL

PUSHROD

HYDRO-BOOST

RETURN LINE

GASKET

HIGH

PRESSURE

LINES

FLATWASHER

PIN

NUTS

LOCKWASHER

WASHER