The parking/emergency brake must hold the
vehicle on any grade. This requirement covers both
passenger and commercial motor vehicles equipped
with either the enclosed type brake at each rear wheel
or a single brake mounted on the drive line. The
Federal Motor Carrier Safety Regulations
Pocketbook, par. 393-52. lists emergency brake
BRAKE SYSTEM INSPECTION
Most vehicle manufacturers recommend periodic
inspection of the brake system. This involves checking
the fluid level in the master cylinder, brake pedal
action, condition of the lines and hoses, and the brake
assemblies. These checks are to be performed during
the preventive maintenance (PM) cycle.
Checking Master Cylinder Fluid Level
An important part of the brake system inspection is
checking the level of the brake fluid. To check the
fluid, remove the master cylinder cover, either by
unbolting the cover or prying off the spring clip. The
brake fluid level should be 1/4 inch from the top of the
Use only the manufacturers recom-
mended type of brake fluid. Keep grease, oil,
or other contaminates out of the brake fluid.
Contamination of the brake fluid can cause
deterioration of the master cylinder cups,
resulting in a sudden loss of braking ability.
Brake Pedal Action
A quick and accurate way to check many of the
components of the brake system is by performing a
brake pedal check. Applying the brake pedal and
comparing its movement to the manufacturers
specifications does this. The three brake pedal
application distances are as follows:
BRAKE PEDAL FREE PLAY, which is the
amount of pedal movement before the beginning of
brake application. It is the difference between the at
rest and initially applied position. Free play is required
to prevent brake drag and overheating. If pedal free play
is NOT correct, check the adjustment of the master
cylinder pushrod. If this adjustment is correct, check for
a worn pedal bushing or a bad return spring, which can
also increase pedal free play.
BRAKE PEDAL HEIGHT, which is the
distance from the pedal to the floor with the pedal at rest.
If the height is incorrect, there may be worn pedal
bushings, weak return springs, or a maladjusted master
BRAKE PEDAL RESERVE DISTANCE,
which is measured from the floor to the brake pedal with
the brake applied. The average brake pedal reserve
distance is 2 inches for manual brakes and 1 inch for
power brakes. If the reserve distance is incorrect, check
the master cylinder pushrod adjustment. Also, there
may be air in the system or the automatic brake adjusters
may not be working.
Brake System Leaks
If the fluid level in the master cylinder is low, you
should check the system for leaks. Check all brake
lines, hoses, and wheel cylinders. Brake fluid leakage
will show up as a darkened, damp area around one of
Checking Brake Assemblies
When inspecting the brake system, remove one of
the front and rear wheels. This will let you inspect the
condition of the brake linings and other components.
INSPECTING DISC BRAKES.Areas
check when inspecting disc brakes are the pads, the
disc, and the caliper. You should check the thickness of
the brake pad linings. Pads should be replaced when
the thinnest (most worn) part of the lining is
approximately 1/8 inch thick.
Check the caliper for fluid leakage at the piston
seal and missing or damaged clips/springs. The disc
should be checked for damage, such as heat cracks,
heat checks (overheating causes small hardened and
cracked areas), and scoring. Wheel bearings should be
checked and adjusted if necessary. To check for rattles,
strike the caliper with a soft-faced rubber mallet. To
repair any of these problems, consult the
manufacturers service manual.
INSPECTING DRUM BRAKES.Areas
check when inspecting drum brakes are the brake
shoes, the brake drums, the wheel cylinders, and other
related parts. Once the wheel is removed, you must
remove the brake drum that will expose all parts
The brake shoe linings must NOT be worn thinner
than 1/16 inch. They also should NOT be glazed or
coated with grease, brake fluid, or differential fluid.
Any of these conditions require lining replacement.