Hummer H2. Manual - part 808

operations on a clean bench, free from all mineral oil materials. Remove the brake caliper from vehicle. 
See BRAKE CALIPER under REMOVAL & INSTALLATION. Drain the brake fluid from the brake 
caliper.  

3.  

Place a 1" (25 mm) block of wood between the caliper and the piston. Install a large C-clamp over the 
body of the brake caliper with the C-clamp ends against the rear of the caliper body and against the block 
of wood. Carefully remove the brake caliper piston by directing low pressure compressed air into the 
brake caliper inlet hole.  

4. Remove the C-clamp form the caliper. Remove the block of wood from the caliper. Install clean cloths to 

pad the interior of the caliper housing between the remaining caliper piston and the caliper body. To 
cover the open caliper bore place a 1" (25 mm) block of wood between the caliper body and the brake 
caliper dust boot seal.  

5. Install a large C-clamp over the body of the brake caliper with the C-clamp ends against the rear of the 

caliper body and against the block of wood. Carefully remove the brake caliper piston by directing low 
pressure compressed air into the brake caliper inlet hole. Remove the C-clamp form the caliper. Remove 
the block of wood from the caliper.  

6.  

Remove the piston boots from the brake caliper. See Fig. 58 . Remove the piston seals from the brake 
caliper. Remove the brake caliper bleeder valve and cap from the brake caliper.  

7.  

Dry the caliper piston bores and counterbores, and the piston with non-lubricated, filtered air. Inspect all 
of the brake caliper parts as follows. Inspect piston for scoring, nicks, cracks, wear or corrosion.  

8. Replace the pistons if any damage is found. Inspect caliper bore for scoring, nicks, cracks, wear, or 

corrosion. Use crocus cloth to polish out light corrosion. Otherwise, replace the caliper. DO NOT hone 
the caliper bore. Seal groove in the caliper bore for nicks or burrs. If found, replace the caliper. 

CAUTION: DO NOT place your fingers in front of the piston in order to catch or 

protect the piston while applying compressed air. This could result in 
serious injury. 

NOTE:

Use clean cloths to pad interior of caliper housing during piston removal. 
Use just enough air to ease the pistons out of the bores. If the pistons are 
blown out, even with the padding provided, it may be damaged. 

CAUTION: Care must be used when removing the piston boot and seal from the 

caliper. Use a small plastic or wood tool for removal. DO NOT use a 
metal tool because it may damage the caliper bore or seal groove. 

CAUTION: DO NOT use abrasives to clean the brake caliper piston. Clean the 

brake caliper piston bore, seal counterbore and the caliper piston 
with denatured alcohol, or equivalent. 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer

  

Fig. 58: Exploded View Of Dual Piston Caliper Assembly 
Courtesy of GENERAL MOTORS CORP. 

Reassembly 

1. Install the brake caliper bleeder valve and bleeder valve cap into the brake caliper. Lubricate the NEW 

piston seal with Delco Supreme 11(R), (GM P/N 12377967) or equivalent DOT-3 brake fluid from a 
clean, sealed brake fluid container.  

2. Install the lubricated, NEW piston seals into the caliper bores. Install the caliper piston into the caliper 

bore. Install the NEW piston dust boot seal over the piston.  

3. Using the Brake Caliper Piston Boot Seal Installer (J-45515), fully seat the piston dust boot seal in the 

caliper. Install the brake caliper to the vehicle. See BRAKE CALIPER under REMOVAL & 
INSTALLATION.  

Disassembly (Rear) 

CAUTION: DO NOT place your fingers in front of the piston in order to catch or 

protect the piston while applying compressed air. This could result in 
serious injury. 

CAUTION: Avoid taking the following actions when you service wheel brake parts: 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer

  

1. Remove the brake caliper from the vehicle. See BRAKE CALIPER under REMOVAL & 

INSTALLATION. Place a thin piece of wood in front of the piston in order to prevent damage. Remove 
the piston by directing compressed air into the brake hose inlet fitting port of the brake caliper housing.  

2. Remove the piston boot. Remove the piston seal. Remove the brake caliper bleed screw cap. Remove the 

brake caliper bleed screw. See Fig. 58 . Inspect the brake caliper bore and the piston seal groove for 
scoring and corrosion. If you find excessive scoring or corrosion around the piston seal area, replace the 
brake caliper housing.  

3. Inspect the brake caliper mounting bracket guide surfaces for corrosion and wear. Remove and replace 

the brake caliper mounting bracket if needed. Clean all the residue from the brake pad guiding surfaces on 
the brake caliper housing and the brake caliper mounting bracket.  

4. Clean all the parts not included in the repair kit with denatured alcohol. Dry all the parts with filtered un-

lubricated compressed air. Blow out all passages in the brake caliper housing and the brake caliper 
bleeder valve.  

Reassembly 

1. Install the brake caliper bleed screw. Tighten the brake caliper bleed screw to specification. See 

TORQUE SPECIFICATIONS . Install the brake caliper bleed screw cap. Lubricate the NEW piston 
seal and the brake caliper bore seal groove with brake fluid, GM P/N 12388967.  

2. Install NEW the seal into the brake caliper bore seal groove. Ensure that the seal is not twisted. Lubricate 

the brake caliper bore and the piston with brake fluid, GM P/N 12388967. See Fig. 58 .  

3. Install the boot and the piston. Install the boot over the end of the piston so that the fold will face toward 

the brake caliper housing piston bore opening. Seat the boot into the brake caliper bore groove. Slide the 
piston into the brake caliper bore. Push down the piston to the bottom of the brake caliper bore.  

4. Ensure that the boot properly seats into the piston groove and into the groove in the brake caliper bore. 

Repeat previous step for the remaining piston. Install the brake caliper to the vehicle. See BRAKE 
CALIPER under REMOVAL & INSTALLATION.  

MASTER CYLINDER 

Disassembly 

DO NOT grind brake linings. DO NOT sand brake linings. DO NOT clean 
wheel brake parts with a dry brush or with compressed air. Some models 
or aftermarket brake parts may contain asbestos fibers which can become 
airborne in dust. Breathing dust with asbestos fibers may cause serious 
bodily harm. Use a water-dampened cloth in order to remove any dust on 
brake parts. Equipment is available commercially in order to perform this 
washing function. These wet methods prevent fibers from becoming 
airborne. 

CAUTION: Brake fluid may irritate eyes and skin. In case of contact, take the 

following actions: Eye contact; rinse thoroughly with water. Skin contact; 
wash with soap and water. If ingested, consult a physician immediately. 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer

  

1. Remove the brake master cylinder from the vehicle. See MASTER CYLINDER under REMOVAL & 

INSTALLATION. Secure the mounting flange of the brake master cylinder in a bench vise so that the 
rear of the primary piston is accessible.  

2. Clean the outside of the master cylinder reservoir on and around the reservoir cap prior to removing the 

cap and diaphragm. Remove the reservoir cap and diaphragm from the reservoir. Inspect the reservoir cap 
and diaphragm for the following conditions. If any of these conditions are present, replace the affected 
components. Cuts or cracks, nicks or deformation.  

3. Remove the master cylinder reservoir from the master cylinder. See MASTER CYLINDER 

RESERVOIR under REMOVAL & INSTALLATION. Using a smooth, round-ended tool, depress the 
primary piston and remove the piston retainer. Remove the primary piston assembly from the cylinder 
bore.  

4. Plug the cylinder inlet ports and the rear outlet port. Apply low pressure, non-lubricated, filtered air into 

the front outlet port, in order the remove the secondary piston with the primary and secondary seals, and 
the return spring. Discard the primary piston assembly, the piston retainer, and the seals and seal retainer 
from the secondary piston.  

Reassembly 

1. DO NOT use abrasives to clean the brake master cylinder bore. Clean the interior and exterior of the 

master cylinder, the secondary piston, and the return spring in denatured alcohol, or equivalent.  

2. Inspect the master cylinder bore, inlet and outlet ports, the secondary piston, and the return spring for 

cracks, scoring, pitting, and/or corrosion. Replace the master cylinder if any of these conditions exist. Dry 
the master cylinder and the individual components with non-lubricated, filtered air.  

3. Lubricate the master cylinder bore, the secondary piston, the return spring, and all of the individual 

overhaul components with Delco Supreme 11(R) (GM P/N 12377967) or equivalent DOT-3 brake fluid 
from a clean, sealed brake fluid container. Assemble the lubricated, NEW primary seal and retainer, and 
NEW secondary seal onto the secondary piston.  

4. Install the lubricated return spring and secondary piston assembly into the cylinder bore. Install the 

lubricated, NEW primary piston assembly into the cylinder bore. Using a smooth, round-ended tool, 
depress the primary piston and install the NEW piston retainer.  

5. Install the master cylinder reservoir to the master cylinder. See MASTER CYLINDER RESERVOIR 

under REMOVAL & INSTALLATION. Install the reservoir cap and diaphragm to the reservoir. Install 
the master cylinder to the vehicle. See MASTER CYLINDER under REMOVAL & INSTALLATION. 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer