Step
| Action
| Yes
| No
|
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.
|
1
| Were you
sent here from a Brake Symptom Table?
| Go to
Step 2
| Go to
Diagnostic Starting Point - Hydraulic Brakes
|
2
| Inspect and adjust the brake fluid level. Refer to
Master Cylinder Reservoir Filling
.
Was the brake fluid level low?
| Go to
Step 3
| Go to
Step 4
|
3
|
- Inspect the brake fluid for the following conditions, indicating
contamination:
| • | Fluid separation indicating two types of fluid are present |
| - | A swirled appearance indicates an oil-based substance |
| - | A layered appearance indicates a silicone-based substance |
| - | A cloudy appearance indicates moisture |
| - | A dark appearance or suspended particles in fluid indicate dirt,
rust, corrosion, or brake dust |
- 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?
| Go to
Step 5
| Go to
Step 6
|
4
|
- Inspect the brake fluid for the following conditions, indicating
contamination:
| • | Fluid separation indicating two types of fluid are present |
| - | A swirled appearance indicates an oil-based substance |
| - | A layered appearance indicates a silicone-based substance |
| - | A cloudy appearance indicates moisture |
| - | A dark appearance or suspended particles in fluid indicate dirt,
rust, corrosion, or brake dust |
- 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?
| Go to
Step 5
| Go to
Step 12
|
5
|
- Flush the hydraulic brake system. Refer to
Hydraulic Brake System Flushing
.
- 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:
| 2.1. | Remove ALL of the following components that utilize rubber seals
or linings. |
| 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 containing rubber
seals or linings. |
| • | 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. |
| • | Replace the brake master cylinder reservoir cap diaphragm. |
- If the brake fluid was NOT contaminated with an oil-based fluid,
but WAS contaminated with water or dirt, 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. Refer to
Hydraulic Brake System Bleeding
.
Did you complete the operation and any required repairs and/or replacements?
| Go to
Step 9
| --
|
6
|
- 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 procedure(s):
| • | Brake master cylinder reservoir cap diaphragm |
- If you repaired or replaced any of the brake system components
listed, bleed the hydraulic brake system. Refer to
Hydraulic Brake System Bleeding
. While bleeding the hydraulic
brake system, observe for the following:
| • | An unrestricted and even flow of brake fluid per axle |
| • | The presence of air in the system at a bleeder screw location
other than at the repair location, except if the brake master cylinder and/or
the proportioning valve was replaced |
Did you find and correct a condition?
| Go to
Step 7
| Go to
Step 12
|
7
| Was there air in the system at a bleeder screw location other than at
the repair location, except if the brake master cylinder and/or the proportioning/combination
valve was replaced?
| Go to
Step 19
| Go to
Step 8
|
8
| Was the
flow of brake fluid unrestricted and even per axle during the bleeding procedure?
| Go to
Step 9
| Go to
Step 10
|
9
| Inspect the hydraulic
function of the brake calipers and the wheel cylinders for proper operation.
Refer to
Hydraulic Brake Component Operation Visual Inspection
.
Was the hydraulic function of the brake calipers and the wheel cylinders
operating properly?
| Go to
Step 21
| Go to
Step 14
|
10
| Was the
flow of brake fluid restricted or uneven through front axle hydraulic components
during the bleeding procedure?
| Go to
Step 13
| Go to
Step 11
|
11
| Was the flow of brake fluid 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 and the wheel cylinders
for proper operation. Refer to
Hydraulic Brake Component Operation Visual Inspection
.
Was the hydraulic function of the brake calipers and the wheel cylinders
operating properly?
| Go to
Step 15
| Go to
Step 13
|
13
| Determine
if the brake caliper is restricting the flow of brake fluid and/or not operating
properly:
- Raise and suitably support the vehicle. Refer to
Lifting and Jacking the Vehicle
in General Information.
- Remove the tire and wheel assemblies. Refer to
Tire and Wheel Removal and Installation
in Tires and Wheels.
- Open the suspected caliper bleeder screw.
- 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.
- Close the caliper bleeder screw.
Was the flow of brake fluid unrestricted and did the caliper piston
move freely?
| Go to
Step 17
| Go to
Step 14
|
14
| Repair or replace any brake caliper/wheel cylinder that was not operating
properly. Refer to the appropriate procedures:
Did you complete the repair and/or replacement?
| Go to
Step 21
| --
|
15
| 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 . Refer to
Hydraulic Brake System Bleeding
.
Was there air in the system?
| Go to
Step 19
| Go to
Step 16
|
16
| Was the flow of brake fluid unrestricted and even per axle during the
bleeding procedure?
| Go to
Step 21
| Go to
Step 17
|
17
|
- Inspect the following hydraulic brake system components for signs
of a fluid restriction; such as being bent, kinked or pinched.
- Replace any of the components listed found to be bent, kinked
or pinched.
- If none of the components listed were bent, kinked or pinched,
replace the hydraulic brake flex hose at the restricted location.
Did you find and correct a condition?
| Go to
Step 21
| Go to
Step 18
|
18
| Replace the proportioning valve. If the vehicle has ABS, refer to
Proportioning Valve Replacement
. If the vehicle
does not have ABS, refer to
Load Sensing Proportioning Valve Replacement
.
Did you complete the replacement?
| Go to
Step 21
| --
|
19
|
- 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.
- Inspect the hydraulic brake system components for evidence of
a recent repair, which may have introduced air into the system.
- Repair or replace any of the components found to be installed
incorrectly or seeping brake fluid.
Did you find and correct a condition?
| Go to
Step 21
| Go to
Step 20
|
20
|
- Inspect the brake master cylinder for internal fluid leaks. Refer
to
Brake System Internal Leak Test
.
- Repair or replace the brake master cylinder if it is found to
be leaking brake fluid internally. Refer to
Master Cylinder Overhaul
or
Master Cylinder Replacement
.
Did you find and correct a condition?
| Go to
Step 21
| Return to Symptom Table
|
21
| Install or connect components that were removed or disconnected
during diagnosis.
Did you complete the operation?
| Hydraulic Brake System OK
Return to Symptom Table
| --
|
