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5-20
Hydraulic Brakes
Brake System Testing
Test the brakes on a roadway that meets all of the
following conditions:
.. Dry
.. Clean
.. Reasonably smooth
" Level
Test the brakes at different vehicle speeds with both
light and heavy brake pedal force.
Do not test the brakes on a roadway with the following
conditions because the tires will not grip the road
equally:
• Wet
., Greasy
.. Covered with loose dirt
Do not test the brakes on a crowned roadway because
the weight of the vehicle will be thrown toward the
wheels on one side.
Do not test the brakes on a rough roadway because
the wheels will tend to bounce.
Brake Pedal Travel
Tools Required
J 28662 Brake Pedal Effort Gauge
One of the following conditions may be the cause of
most low brake pedal problems:
.. Air in the brake system. Bleed the system until the
air is purged. Refer to Hydraulic Brake System
Bleeding (Manual Bleeding) or Hydraulic
Brake System Bleeding (Pressure Bleeding).
" Misadjusted rear drum brakes. Inspect the rear
brake adjustment.
The following conditions may be other less frequent
causes of excessive brake pedal travel:
• Incorrect pushrod length
• Malfunctioning rear brake shoe adjusters
" Excessively worn pads
" Brake hydraulic system leakage
One of the following conditions is usually the cause of
high brake pedal effort problems:
.. Low engine vacuum
.. Vacuum leak
" Improperly functioning vacuum booster
1. Install the J 28662 onto the brake pedal.
2. Hook the end of the tape measure over the top
edge of the pedal.
3. Measure the distance from the top edge of the
pedal to the rim of the steering wheel.
4. Block the tires and the wheels.
5. Run the engine at idle.
6. Put the range selector lever in NEUTRAL.
7. Apply 445 N (100 lb) of force to the brake pedal.
8. Remeasure the distance from the top edge of
the pedal to the rim of the steering wheel. The
difference between both of the readings is
the actual brake pedal travel. The brake pedal
travel should be between 51-89 mm (2.0-3.5 in).
Brakes
Brake Fluid Leak
1. Run the engine at idle.
2. Put the range selector lever in NEUTRAL .
3. Depress the brake pedal. Hold the brake pedal
with constant foot pressure.
4. If the pedal gradually falls away with constant
pressure, the brake hydraulic system may be
leaking. Inspect the hydraulic system for
any suspected leaks.
5. Inspect the master cylinder fluid level.
• A slight drop in the master cylinder resewoir
level results from normal pad wear. The
reservoir may be as low as 25.4 mm (1.0 in)
from the top if the pads are worn. This
condition is not abnormal.
• An abnormally low level in the reservoir
indicates a leak in the system. The brake
hydraulic system may be leaking either
internally or externally. Refer toHydrau/ic Brake.
Diagnostic System Check. The system may
appear to pass this test but still h~ve a slight
leakage.
6. Inspect the brake pipe and the brake hose
connections for brake fluid Jeaks.
7. If any leaks are found, replace the hose or the pipe.
8: If any hoses or pipes are replaced, inspect the
connecting brake component for damage. If
damage is found, rebuild or replace the
component.
9. Inspect the brake caliper boots and rear wheel
cylinder boots for leaks.
10. If any leaks are found, rebuild or replace the part
in question. Refer to Disc Brakes.
Brake Hose and Pipe Inspection ·
Notice: Do not allow components to hang from the
flexible brake hoses as damage to the hoses
may occur. Some brake hoses have protective rings
or covers to prevent direct contact ofthe hose
with other chassis parts. Besides causing possible
structural damage to the hose, excessive tension could
cause the hose rings to move out of their proper
locations .
Inspect the brake hoses at least twice a year for the
following conditions:
• Road hazard damage
• Cracks
• Chafing of the outer cover
• Leaks
• Blisters
Use a light and a mirror for an adequate inspection.
Replace any hoses with any of the above conqitions.
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