Hummer H2. Manual — part 786

See BRAKE ROTOR THICKNESS MEASUREMENT under ADJUSTMENTS & INSPECTION. If
the brake rotor exhibits thickness variation that exceeds the maximum acceptable level, go to step 17 . If
the brake rotor does not exhibit thickness variation that exceeds the maximum acceptable level, go to step
16 .

16. Make the following determination individually for each rotor:

z

Heavy rust and/or pitting.

z

Cracks and/or heat spots.

z

Excessive blueing discoloration.

z

Deep or excessive scoring beyond maximum acceptable level.

Make a determination for each brake rotor if the rotor requires refinishing based upon the results of the
inspection. If the brake rotor exhibits any of the conditions listed previously, it requires refinishing. If the
brake rotors require refinishing, go to step 17 . If the brake rotors DO NOT require finishing, go to step
22 .

17.

z

Refinish the brake rotor. See BRAKE ROTOR REFINISHING under OVERHAUL.

z

Inspect the brake rotor thickness. See BRAKE ROTOR THICKNESS MEASUREMENT under
ADJUSTMENTS & INSPECTION.

If you were able to refinish the brake rotor within the minimum requirements, go to step 22 . If you were
not able to refinish the brake rotor within the minimum requirements, go to step 21 .

18. If the brake rotor is at or below the discard requirements, go to step 21 . If the brake rotor is not at or

below the discard requirements, go to step 19 .

19.

Inspect each of the disc brake rotors for thickness variation that exceeds the maximum acceptable level.
See BRAKE ROTOR THICKNESS MEASUREMENT under ADJUSTMENTS & INSPECTION. If
the brake rotor exhibits thickness variation that exceeds the maximum acceptable level, go to step 21 . If
the brake rotor does not exhibit thickness variation that exceeds the maximum acceptable level, go to step
20 .

20.

A. Inspect each of the disc brake rotors for the following surface and wear conditions:

z

Heavy rust and/or pitting.

z

Cracks and/or heat spots.

z

Excessive blueing discoloration.

z

Deep or excessive scoring beyond maximum acceptable level.

See BRAKE ROTOR SURFACE & WEAR INSPECTION under ADJUSTMENTS &
INSPECTION.

B. Make a determination for each brake rotor if the rotor requires replacement based upon the results

of the inspection. If the brake rotor exhibits any of the conditions listed previously, it requires
replacement. If the brake rotor requires replacement, go to step 21 . If the brake rotor does not
require replacement, go to step 22 .

NOTE:

Make the following determination individually for each rotor.

2004 Hummer H2

2003-04 BRAKES Disc - Hummer

21.

Replace the brake rotor. See BRAKE ROTOR . After repairs are complete, go to step 24 .

22.

Inspect each of the disc brake rotors for assembled LRO that exceeds the maximum acceptable level. See
appropriate ANTI-LOCK article. If the brake rotor exhibits assembled LRO that exceeds the maximum
acceptable level, go to step 23 . If the brake rotor does not exhibit assembled LRO that exceeds the
maximum acceptable level, go to step 24 .

23. Correct the LRO for each brake rotor that was determined to have LRO exceeding the maximum

acceptable level. See appropriate ANTI-LOCK article. If the operation was completed, go to step 24 .

24. Install or connect components that were removed or disconnected during diagnosis. If the operation was

completed, disc brake system okay. If the operation was not completed, return to symptom list.

HYDRAULIC BRAKE SYSTEM DIAGNOSIS

1. If were you sent here from a brake symptom test, go to step 2 . If you were not sent here from a brake

symptom test, see HYDRAULIC BRAKE SYSTEM under GENERAL DIAGNOSIS.

2. Inspect and adjust the brake fluid level in the brake master cylinder. See MASTER CYLINDER

RESERVOIR FILLING under BLEEDING BRAKE SYSTEM. If the brake fluid level was low, go to
step 3 . If the brake fluid level was not low, go to step 4 .

3. Inspect the brake fluid for the following conditions, indicating brake fluid contamination:

A. Fluid separation, indicating 2 types of fluid are present:

z

Swirled appearance, oil-based substance.

z

Layered appearance, silicone-based substance.

B. Fluid discoloration:

z

Cloudy appearance, moisture.

z

Dark appearance/suspended particles in fluid, dirt, rust, corrosion and brake dust.

Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for
swelling, indicating fluid contamination. If any of the above conditions exist, go to step 5 . If any of the
above conditions DO NOT exist, go to step 6 .

4. Inspect the brake fluid for the following conditions, indicating brake fluid contamination:

A. Fluid separation, indicating 2 types of fluid are present:

z

Swirled appearance, oil-based substance.

z

Layered appearance, silicone-based substance.

B. Fluid discoloration:

z

Cloudy appearance, moisture.

NOTE:

Whenever a brake rotor is replaced, the assembled Lateral Runout (LRO)
of the rotor must be measured to ensure optimum performance of the disc
brakes. See appropriate ANTI-LOCK article.

NOTE:

Make the following determination individually for each rotor.

2004 Hummer H2

2003-04 BRAKES Disc - Hummer

z

Dark appearance/suspended particles in fluid, dirt, rust, corrosion and brake dust.

Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for
swelling, indicating fluid contamination. If any of the above conditions exist, go to step 5 . If any of the
above conditions DO NOT exist, go to step 12 .

5. Flush the hydraulic brake system. See HYDRAULIC BRAKE SYSTEM FLUSHING under

BLEEDING BRAKE SYSTEM. If the brake fluid WAS contaminated with an oil-based or a silicone-
based fluid, indicated by fluid separation and/or a swollen master cylinder reservoir cap diaphragm and/or
swollen reservoir-to-master cylinder grommets, perform the following steps. Refer to the procedures
indicated:

z

Remove all of the following components listed. Each component contains internal rubber
seals/linings which have been contaminated.

z

Clean out the hydraulic brake pipes using denatured alcohol, or equivalent.

z

Dry the brake pipes using non-lubricated, filtered air.

z

Repair or replace all of the following components listed. Each component contains internal rubber
seals/linings which have been contaminated.

A. Perform master cylinder overhaul and/or master cylinder replacement. See MASTER

CYLINDER under OVERHAUL; or MASTER CYLINDER under REMOVAL &
INSTALLATION.

B. Clean the brake master cylinder reservoir using denatured alcohol, or equivalent, then dry the

reservoir using non-lubricated, filtered air, or if necessary, replace the brake master cylinder
reservoir. See MASTER CYLINDER RESERVOIR under REMOVAL &
INSTALLATION.

C. Replace the brake master cylinder reservoir cap diaphragm.

D. Replace front and/or rear brake hose. See BRAKE HOSE under REMOVAL &

INSTALLATION.

E. Perform front and/or rear brake caliper overhaul. See BRAKE CALIPER under

OVERHAUL. Replace front and/or rear brake caliper. See BRAKE CALIPER under
REMOVAL & INSTALLATION.

F. Replace Brake Pressure Modulator Valve (BPMV). See appropriate ANTI-LOCK article.

If the brake fluid was NOT contaminated with an oil-based fluid, but was contaminated with water or dirt,
rust, corrosion, and/or brake dust, replace the brake master cylinder reservoir cap diaphragm which may
have allowed moisture or dirt to enter the system. Refill and bleed the hydraulic brake system. See
BLEEDING BRAKE SYSTEM . If the operation and any required repairs and/or replacements were
completed, go to step 9 .

6.

A. Inspect the following hydraulic brake system components for external fluid leaks. Repair or replace

any of the components found to be leaking brake fluid. Refer to the appropriate procedures:

z

Perform master cylinder overhaul and/or master cylinder replacement. See MASTER
CYLINDER under OVERHAUL; or MASTER CYLINDER under REMOVAL &
INSTALLATION.

z

Replace front and/or rear brake hose. See BRAKE HOSE under REMOVAL &
INSTALLATION.

2004 Hummer H2

2003-04 BRAKES Disc - Hummer

z

Replace Brake Pipe. See BRAKE PIPE under REMOVAL & INSTALLATION.

z

Perform front and/or rear brake caliper overhaul. See BRAKE CALIPER under
OVERHAUL. Replace front and/or rear brake caliper. See BRAKE CALIPER under
REMOVAL & INSTALLATION.

z

Replace Brake Pressure Modulator Valve (BPMV). See BRAKE PRESSURE
MODULATOR VALVE. See appropriate ANTI-LOCK article.

B. If you repaired or replaced any of the brake system components listed, bleed the hydraulic brake

system. See BLEEDING BRAKE SYSTEM . While bleeding the hydraulic brake system, observe
for the following conditions:

z

The presence of air in the system at a bleeder valve location other than at the repair location,
except if the brake master cylinder was replaced.

z

An unrestricted and even flow of brake fluid per axle during the bleeding procedure.

If the condition was found and corrected, go to step 7 . If the condition was not found and corrected, go to
step 12 .

7. If there was air in the system at a bleeder valve location other than at the repair location, except if the

brake master cylinder was replaced, go to step 19 . If there was nor air in the system at a bleeder valve
location other than at the repair location, except if the brake master cylinder was replaced, go to step 8 .

8. If the flow of brake fluid was unrestricted and even per axle during the bleeding procedure, go to step 9 .

If the flow of brake fluid was not unrestricted and even per axle during the bleeding procedure, go to step
10 .

9. Inspect the hydraulic function of the brake calipers for proper operation. See HYDRAULIC BRAKE

COMPONENT OPERATION VISUAL INSPECTION under ADJUSTMENTS & INSPECTION. If
the hydraulic function of the brake calipers was operating properly, go to step 21 . If the hydraulic
function of the brake calipers was not operating properly, go to step 14 .

10. If the flow of brake fluid was restricted or uneven through front axle hydraulic components during the

bleeding procedure, go to step 13 . If the flow of brake fluid was not restricted or uneven through front
axle hydraulic components during the bleeding procedure, go to step 11 .

11. If the flow of brake fluid was restricted or uneven through rear axle hydraulic components during the

bleeding procedure, go to step 17 .

12. Inspect the hydraulic function of the brake calipers for proper operation. See HYDRAULIC BRAKE

COMPONENT OPERATION VISUAL INSPECTION under ADJUSTMENTS & INSPECTION. If
the hydraulic function of the brake calipers are operating properly, go to step 15 . If the hydraulic function
of the brake calipers are not operating properly, go to step 13 .

13. Determine if the brake caliper is restricting the flow of brake fluid and/or not operating properly:

z

Raise and support the vehicle.

z

Remove the tire and wheel assemblies.

z

Open the suspected caliper bleeder valve.

z

Using a large C-clamp, compress the caliper piston and observe for an unrestricted flow of brake
fluid and for free movement of the caliper piston.

z

Close the caliper bleeder valve.

If the flow of brake fluid was unrestricted and if the caliper piston moved freely, go to step 17 . If the
flow of brake fluid was not unrestricted and if the caliper piston did not move freely, go to step 14 .

2004 Hummer H2

2003-04 BRAKES Disc - Hummer