Step
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Action
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Yes
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No
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DEFINITION: This diagnostic table is designed to diagnose ONLY the
components of the HYDRAULIC brake system in order to determine if
the HYDRAULIC brake system is operating properly. You will be
directed by the appropriate Symptom table to go to other brake
system diagnostic tables as appropriate.
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1
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Were you sent here from a Brake Symptom table?
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Go to Step 2
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2
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Inspect and adjust the brake fluid level in the brake master
cylinder. Refer to
Master Cylinder Reservoir Filling .
Was the brake fluid level low?
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Go to Step 5
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Go to Step 3
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3
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1. |
Inspect the brake fluid for the following
conditions, indicating brake fluid contamination: |
| • |
Fluid separation, indicating two types of fluid
are present |
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Swirled appearance - oil-based substance |
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Layered appearance - silicone-based substance |
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Cloudy appearance - moisture |
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Dark appearance/suspended particles in fluid - dirt, rust,
corrosion, brake dust |
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2. |
Inspect the master cylinder reservoir cap
diaphragm and the reservoir-to-master cylinder grommets for
swelling, indicating fluid contamination. |
Do any of the above conditions exist?
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Go to Step 4
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Go to Step 5
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4
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2. |
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. |
| 2.1. |
Remove ALL of the following components listed.
Each component contains internal rubber seals/linings which have
been contaminated. |
| 2.2. |
Clean out the hydraulic brake pipes using
denatured alcohol, or equivalent. |
| 2.3. |
Dry the brake pipes using non-lubricated, filtered
air. |
| 2.4. |
Repair or replace ALL of the following components
listed. Each component contains internal rubber seals/linings which
have been contaminated. |
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Replace the brake master cylinder reservoir cap diaphragm. |
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Brake master cylinder reservoir: 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. Refer to
Master Cylinder Reservoir Replacement . |
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3. |
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. |
Did you complete the operation and any required repairs and/or
replacements?
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Go to Step 6
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5
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1. |
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: |
| • |
Brake master cylinder reservoir cap diaphragm |
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2. |
If you repaired or replaced any of the brake
system components listed, bleed the hydraulic brake system. Refer
to . While bleeding the hydraulic brake system, observe for the
following conditions:
Hydraulic Brake System Bleeding |
| • |
The presence of air in the system at a bleeder
valve location other than at the repair location, except if the
brake master cylinder, and/or the proportioning valve assembly, was
replaced |
| • |
An unrestricted and even flow of brake fluid per
axle during the bleeding procedure |
Did you find and correct a condition?
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Go to Step 6
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Go to Step 8
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6
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Was there air in the system at a bleeder valve location other than
at the repair location, except if the brake master cylinder, and/or
the proportioning valve assembly, was replaced?
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Go to Step 17
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Go to Step 7
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7
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Was the flow of brake fluid unrestricted and even per axle during
the bleeding procedure?
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Go to Step 8
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Go to Step 9
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8
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Inspect the hydraulic function of the brake calipers and/or wheel
cylinders, if equipped for proper operation. Refer to
Hydraulic Brake Component Operation Visual Inspection .
Was the hydraulic function of the brake calipers/wheel cylinders
operating properly?
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Go to Step 19
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Go to Step 12
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9
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Was the flow of brake fluid restricted or uneven through front
axle hydraulic components during the bleeding procedure?
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Go to Step 11
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Go to Step 10
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10
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Was the flow of brake fluid restricted or uneven through rear axle
hydraulic components during the bleeding procedure?
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Go to Step 15
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11
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Determine if the brake caliper is restricting the flow of brake
fluid and/or not operating properly:
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3. |
Open the suspected caliper bleeder valve. |
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4. |
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. |
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5. |
Close the caliper bleeder valve. |
Was the flow of brake fluid unrestricted and did the caliper
piston move freely?
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Go to Step 15
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Go to Step 12
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12
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Repair or replace any brake caliper/wheel cylinder that was not
operating properly. Refer to the appropriate procedure.
Did you complete the repair and/or replacement?
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Go to Step 19
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13
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Bleed the hydraulic brake system to observe for the presence of
air in the system and to observe for an unrestricted and even flow
of brake fluid per axle during the bleeding procedure. Refer to
Hydraulic Brake System Bleeding .
Was there air in the system?
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Go to Step 17
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Go to Step 14
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14
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Was the flow of brake fluid unrestricted and even per axle during
the bleeding procedure?
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Go to Step 19
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Go to Step 15
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15
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1. |
Inspect the hydraulic brake pipes and flexible
brake hoses for signs of a fluid restriction; such as being bent,
kinked, pinched or damaged. Refer to .
Brake Pipe and Hose Inspection |
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2. |
Replace any of the hydraulic brake pipes and/or
flexible brake hoses found to be bent, kinked, pinched, or damaged.
Refer to the following procedures as necessary: |
|
3. |
If none of the hydraulic brake pipes or flexible
brake hoses were visibly bent, kinked, pinched, or damaged, replace
the hydraulic brake flex hose at the restricted location. |
Did you find and correct a condition?
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Go to Step 19
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Go to Step 16
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16
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Replace the brake modulator assembly, in order to correct the
hydraulic brake dynamic rear proportioning mechanical operation.
Refer to
Brake Pressure Modulator Valve Replacement .
Did you complete the replacement?
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Go to Step 19
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17
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1. |
Inspect the hydraulic brake system components for
brake fluid seepage at a seal and/or fitting location, which may
have drawn air into the system. |
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2. |
Inspect the hydraulic brake system components for
evidence of a recent repair, which may have introduced air into the
system. |
|
3. |
Repair or replace any of the components found to
be installed incorrectly or seeping brake fluid. |
Did you find and correct a condition?
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Go to Step 19
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Go to Step 18
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18
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2. |
Repair or replace the brake master cylinder if it
is found to be leaking brake fluid internally. Refer to .
Master Cylinder Replacement |
Did you find and correct a condition?
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Go to Step 19
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Return to Symptom Table
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19
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Install or connect components that were removed or disconnected
during diagnosis.
Did you complete the operation?
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Hydraulic Brake System OK
Return to Symptom Table
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