Hummer H2. Manual - part 778

1. Place a clean shop cloth beneath the brake master cylinder to prevent brake fluid spills. With the ignition 

OFF and the brakes cool, apply the brakes 3-5 times, or until the brake pedal effort increases 
significantly, in order to deplete the brake booster power reserve.  

2. If you have performed a brake master cylinder bench bleeding on this vehicle, or if you disconnected the 

brake pipes from the master cylinder, you must perform the following steps: 

A. Ensure that the brake master cylinder reservoir is full to the maximum-fill level. If necessary, add 

Delco Supreme 11(R) (GM P/N 12377967) or equivalent DOT-3 brake fluid from a clean, sealed 
brake fluid container. If removal of the reservoir cap and diaphragm is necessary, clean the outside 
of the reservoir on and around the cap prior to removal.  

B. With the rear brake pipe installed securely to the master cylinder, loosen and separate the front 

brake pipe from the front port of the brake master cylinder.  

C. Allow a small amount of brake fluid to gravity bleed from the open port of the master cylinder.  

D. Reconnect the brake pipe to the master cylinder port and tighten securely.  

E. Have an assistant slowly depress the brake pedal fully and maintain steady pressure on the pedal.  

F. Loosen the same brake pipe to purge air from the open port of the master cylinder.  

G. Tighten the brake pipe, then have the assistant slowly release the brake pedal.  

H. Wait 15 seconds, then repeat steps C - G until all air is purged from the same port of the master 

cylinder.  

I. With the front brake pipe installed securely to the master cylinder, after all air has been purged 

from the front port of the master cylinder, loosen and separate the rear brake pipe from the master 
cylinder, then repeat steps C - H  

J. After completing the final master cylinder port bleeding procedure, ensure that both of the brake 

pipe-to-master cylinder fittings are properly tightened.  

3. Fill the brake master cylinder reservoir with Delco Supreme 11(R) (GM P/N 12377967), or equivalent 

DOT-3 brake fluid from a clean, sealed brake fluid container. Ensure that the brake master cylinder 
reservoir remains at least half-full during this bleeding procedure. Add fluid as needed to maintain the 
proper level. Clean the outside of the reservoir on and around the reservoir cap prior to removing the cap 
and diaphragm.  

4. Install a proper box-end wrench onto the RIGHT REAR wheel hydraulic circuit bleeder valve.  

5. Install a transparent hose over the end of the bleeder valve.  

6. Submerge the open end of the transparent hose into a transparent container partially filled with Delco 

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

7. Have an assistant slowly depress the brake pedal fully and maintain steady pressure on the pedal.  

8. Loosen the bleeder valve to purge air from the wheel hydraulic circuit. 

CAUTION: When adding fluid to the brake master cylinder reservoir, use only Delco 

Supreme 11(R) (GM P/N 12377967), or equivalent DOT-3 brake fluid from a 
clean, sealed brake fluid container. The use of any type of fluid other than 
the recommended type of brake fluid, may cause contamination which 
could result in damage to the internal rubber seals and/or rubber linings of 
hydraulic brake system components. 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer

  

9. Tighten the bleeder valve, then have the assistant slowly release the brake pedal.  

10. Wait 15 seconds, then repeat steps 8 - 10 until all air is purged from the same wheel hydraulic circuit.  

11. With the right rear wheel hydraulic circuit bleeder valve tightened securely, after all air has been purged 

from the right rear hydraulic circuit, install a proper box-end wrench onto the LEFT FRONT wheel 
hydraulic circuit bleeder valve.  

12. Install a transparent hose over the end of the bleeder valve, then repeat steps 7 - 11 .  

13. With the left front wheel hydraulic circuit bleeder valve tightened securely, after all air has been purged 

from the left front hydraulic circuit, install a proper box-end wrench onto the LEFT REAR wheel 
hydraulic circuit bleeder valve.  

14. Install a transparent hose over the end of the bleeder valve, then repeat steps 7 - 11 .  

15. With the right front wheel hydraulic circuit bleeder valve tightened securely, after all air has been purged 

from the left rear hydraulic circuit, install a proper box-end wrench onto the RIGHT FRONT wheel 
hydraulic circuit bleeder valve.  

16. Install a transparent hose over the end of the bleeder valve, then repeat steps 7 - 11 .  

17. After completing the final wheel hydraulic circuit bleeding procedure, ensure that each of the 4 wheel 

hydraulic circuit bleeder valves are properly tightened.  

18. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11(R) (GM P/N 

12377967), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.  

19. Slowly depress and release the brake pedal. Observe the feel of the brake pedal.  

20. If the brake pedal feels spongy, repeat the bleeding procedure again. If the brake pedal still feels spongy 

after repeating the bleeding procedure, perform the following steps: 

A. Inspect the brake system for external leaks. See BRAKE SYSTEM EXTERNAL LEAK 

INSPECTION under ADJUSTMENT & INSPECTION.  

B. Pressure bleed the hydraulic brake system in order to purge any air that may still be trapped in the 

system.  

21. Turn the ignition key ON, with the engine OFF. Check to see if the brake system warning light remains 

illuminated.  

22.  

If the brake system warning light remains illuminated, see BRAKE WARNING INDICATOR 
ALWAYS ON under SYMPTOM TESTS.  

PRESSURE BLEEDING 

CAUTION: DO NOT allow the vehicle to be driven until it is diagnosed and 

repaired 

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, 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer

  

1. Place a clean shop cloth beneath the brake master cylinder to prevent brake fluid spills.  

2. With the ignition OFF and the brakes cool, apply the brakes 3-5 times, or until the brake pedal effort 

increases significantly, in order to deplete the brake booster power reserve.  

3. If you have performed a brake master cylinder bench bleeding on this vehicle, or if you disconnected the 

brake pipes from the master cylinder, you must perform the following steps: 

A. Ensure that the brake master cylinder reservoir is full to the maximum-fill level. If necessary, add 

Delco Supreme 11(R) (GM P/N 12377967), or equivalent DOT-3 brake fluid from a clean, sealed 
brake fluid container. If removal of the reservoir cap and diaphragm is necessary, clean the outside 
of the reservoir on and around the cap prior to removal.  

B. With the rear brake pipe installed securely to the master cylinder, loosen and separate the front 

brake pipe from the front port of the brake master cylinder.  

C. Allow a small amount of brake fluid to gravity bleed from the open port of the master cylinder.  

D. Reconnect the brake pipe to the master cylinder port and tighten securely.  

E. Have an assistant slowly depress the brake pedal fully and maintain steady pressure on the pedal.  

F. Loosen the same brake pipe to purge air from the open port of the master cylinder.  

G. Tighten the brake pipe, then have the assistant slowly release the brake pedal.  

H. Wait 15 seconds, then repeat steps C - G until all air is purged from the same port of the master 

cylinder.  

I. With the front brake pipe installed securely to the master cylinder, after all air has been purged 

from the front port of the master cylinder, loosen and separate the rear brake pipe from the master 
cylinder, then repeat steps C - H .  

J. After completing the final master cylinder port bleeding procedure, ensure that both of the brake 

pipe-to-master cylinder fittings are properly tightened.  

4. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11(R) (GM P/N 

12377967), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container. Clean the outside 
of the reservoir on and around the reservoir cap prior to removing the cap and diaphragm.  

5. Install the Master Cylinder Bleeder Adapter (J-35589-A) to the brake master cylinder reservoir.  

6. Check the brake fluid level in the Diaphragm Type Brake Pressure Bleeder (J-29532), or equivalent. Add 

Delco Supreme 11(R) (GM P/N 12377967), or equivalent DOT-3 brake fluid from a clean, sealed brake 
fluid container as necessary to bring the level to approximately the half-full point.  

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. 

CAUTION: When adding fluid to the brake master cylinder reservoir, use only Delco 

Supreme 11(R) (GM P/N 12377967), or equivalent DOT-3 brake fluid from a 
clean, sealed brake fluid container. The use of any type of fluid other than 
the recommended type of brake fluid, may cause contamination which 
could result in damage to the internal rubber seals and/or rubber linings of 
hydraulic brake system components. 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer

  

7. Connect the diaphragm type brake pressure bleeder, or equivalent, to the master cylinder bleeder adapter. 

8. Charge the diaphragm type brake pressure bleeder, or equivalent, air tank to 25-30 Psi (175-205 kPa).  

9. Open the diaphragm type brake pressure bleeder, or equivalent, fluid tank valve to allow pressurized 

brake fluid to enter the brake system.  

10. Wait approximately 30 seconds, then inspect the entire hydraulic brake system in order to ensure that 

there are no existing external brake fluid leaks. Any brake fluid leaks identified require repair prior to 
completing this procedure.  

11. Install a proper box-end wrench onto the RIGHT REAR wheel hydraulic circuit bleeder valve.  

12. Install a transparent hose over the end of the bleeder valve.  

13. Submerge the open end of the transparent hose into a transparent container partially filled with Delco 

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

14. Loosen the bleeder valve to purge air from the wheel hydraulic circuit. Allow fluid to flow until air 

bubbles stop flowing from the bleeder, then tighten the bleeder valve.  

15. With the right rear wheel hydraulic circuit bleeder valve tightened securely, after all air has been purged 

from the right rear hydraulic circuit, install a proper box-end wrench onto the LEFT REAR wheel 
hydraulic circuit bleeder valve.  

16. Install a transparent hose over the end of the bleeder valve, then repeat steps 13 - 14 .  

17. With the left rear wheel hydraulic circuit bleeder valve tightened securely, after all air has been purged 

from the left front hydraulic circuit, install a proper box-end wrench onto the RIGHT FRONT wheel 
hydraulic circuit bleeder valve.  

18. Install a transparent hose over the end of the bleeder valve, then repeat steps 13 - 14 .  

19. With the right front wheel hydraulic circuit bleeder valve tightened securely, after all air has been purged 

from the left rear hydraulic circuit, install a proper box-end wrench onto the LEFT FRONT wheel 
hydraulic circuit bleeder valve.  

20. Install a transparent hose over the end of the bleeder valve, then repeat steps 13 - 14 .  

21. After completing the final wheel hydraulic circuit bleeding procedure, ensure that each of the 4 wheel 

hydraulic circuit bleeder valves are properly tightened.  

22. Close the diaphragm type brake pressure bleeder, or equivalent, fluid tank valve, then disconnect the 

diaphragm type brake pressure bleeder, or equivalent, from the master cylinder bleeder adapter.  

23. Remove the master cylinder bleeder adapter from the brake master cylinder reservoir.  

24. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11(R) (GM P/N 

12377967), DOT-3 brake fluid from a clean, sealed brake fluid container.  

25. Slowly depress and release the brake pedal. Observe the feel of the brake pedal.  

26. If the brake pedal feels spongy perform the following steps: 

z

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

z

Using a scan tool, perform the anti-lock brake system automated bleeding procedure to remove any 
air that may have been trapped in the BPMV. See appropriate See ANTI-LOCK article in 
BRAKES.  

27. Turn the ignition key ON, with the engine OFF. Check to see if the brake system warning light remains 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer