The American Driver
From Drivers...For Drivers
WITHIN AN INCH OF YOUR LIFE

TRUCKERS! Poorly adjusted brakes could cost you time and money with out-of-service violations, jeopardize your safety and that of others
due to impaired stopping ability, and even cost you your life. The only way to be sure that your vehicle’s brakes are properly adjusted is to
physically check each wheel on a regular schedule. It is difficult for you to sense, simply from pedal feel, that your brakes are out of
adjustment. Under normal braking conditions, your brakes may respond satisfactorily, but under a hard or panic stop you may find that
you are unable to stop in time.

HOW TO CHECK

Before checking or making adjustments, be sure that your vehicle is parked on a level surface with the wheels blocked, spring brakes
released, and the engine shut off. The following measurements are for Type 30 air chamber brakes only. For other types, check with your
mechanic, supervisor, or manufacturer.

One person method: (1) Pull the chamber pushrod to its limit by hand or by prying with a short pry bar. (2) Measure from the clevis pin to
the chamber face at both full retraction and at full extension. The difference between these measurements is the pushrod travel or slack.
One-half inch is correct, and the MAXIMUM ALLOWABLE TRAVEL IS ONE INCH (one-person method).

Two-person method: Make the same measurements described in the one-person method, but with brakes fully applied and with brakes
released. Because of the considerable stretching and bending of various parts when using the two-person method, the MAXIMUM
ALLOWABLE TRAVEL IS TWO INCHES for Type 30 air chamber brakes.

HOW TO ADJUST

Brake adjustment, or “taking up the slack,” is done by first making sure the brakes are released, then turning the adjusting bolt on the
slack adjuster arm:
(
1) Depress the spring locking sleeve with a wrench.
  • open-end wrench is the ideal tool
  • depending on the slack adjuster type...wrench size: 9/16th, 7/16th or 3/8th
(2) Tighten the bolt until solid resistance is met. This indicates that the brake linings are touching the drum.
(
3) Restore running clearance by backing off the adjustment between one-quarter and one-half a turn. Re-check the pushrod travel.
Proper adjustment leaves one-half an inch.
(
4) Check each brake drum or rotor for excessive heat soon after the brakes have been adjusted. An extra-hot brake drum means that you
have adjusted the brakes too tightly.

NOTE: Most adjusting bolts require a normal clockwise turn to “set up” the brakes, but some require a counter-clockwise turn. Be alert for
any outward movement of the chamber pushrod and slack adjuster arm while the adjustment bolt is being turned. This movement means
you are turning in the wrong direction.

For both this type and other types of brake systems, always check with the manufacturer for proper maintenance and adjustment
procedures. If you are not comfortable with these procedures, ask your mechanic or supervisor.
IF BRAKE SLACK EXCEEDS ONE INCH, YOU COULD BE DRIVING A “KILLER TRUCK”.
THIS IS THE MOST IMPORTANT INCH OF YOUR LIFE.
BRAKES SHOULD BE CHECKED BEFORE EACH TRIP AND MORE FREQUENTLY IN HILLY AREAS.