User's Manual

47
Date of Origin – 02/01/08
CHECKING SPRING BRAKES
Spring breaks must be inspected on a routine basis to insure proper operation. Inspection is
recommended a minimum of every 3 months or 25,000 miles.
WARNING! Always chock wheels to prevent the vehicle from rolling before per-
forming any brake maintenance.
1. Check overall condition of the foundation brakes including drums, shoes, lining, retainers, return
springs, bushings and rollers. Replace any damaged or worn components per manufacturer’s
specifications.
2. Check for obvious structural damage to the spring brakes, brake adjusters, or cam shafts and
replace any damaged or worn components per manufacturer’s specifications.
3. Hook up appropriate air supply and release parking brakes. Apply and fully release Parking Brake
several times while watching for brake adjuster movement. Adjusters should apply and retract at
relatively the same distance for all wheel positions.
4. To verify equal push rod movement, measure each push rod from the Face of the Air Brake Cham-
ber to the Center of the Clevis Pin with the brakes Fully Set or Parked. Apply air to the chambers to
release the parking brakes and re-measure all wheel positions. All strokes should be within 1/8" of
each other.
5. Applied Stroke at 90 to 100 psi can also be used to measure in a similar way as in step #4. Apply
Service Brakes instead of setting Spring (Emergency) Brakes and record before and after push
rod measurements. Measured push rod stroke should not exceed the recommended maximum
readjustment limit of 2" for Standard 30/30 chambers and 2 1/2" for Long Stroke 30/30 chambers.
AUTOMATIC SLACK ADJUSTERS
Effective 10/20/94 all semi-trailers with air brake systems were required to be built with automatic
slack adjusters to assist in maintaining the braking system performance. The automatic slack
adjusters should be periodically checked to insure that they are performing correctly and should
be lubricated on a regular schedule or at least every six months.
The following procedure can be used to check the in-service adjustment of air chamber push rod
travel (adjusted chamber stroke) on trailer air brakes with automatic slack adjusters.
1. Connect an adequate air supply to the SUPPLY glad hand of the trailer’s air system.
2. Increase the air pressure to 100 psi minimum to release the auxiliary spring brake cham-
bers.
3. Determine the size and type of brake chamber you are inspecting.
4. With the brakes NOT APPLIED measure the distance from the bottom of the air brake
chamber to the center of the large clevis pin on all wheel positions. Record each measure-
ment.
5. Connect a second air supply to the CONTROL glad hand of the trailer’s air system.
6. Increase the air pressure of the second air supply to 85 to 90 psi to apply the service
brakes.
7. With the SERVICE BRAKES APPLIED measure the distance from the bottom of the air
brake chamber to the center of the large clevis pin on all wheel positions. Record each
measurement.
8. Calculate the adjusted chamber stroke of each brake. Subtract the dimension that was
measured in Step #3 from the dimension that was measured in Step #6. The difference
between the two dimensions is the adjusted air brake chamber stroke. The adjusted air
brake chamber stroke must not be greater than 2” for 30/30 chambers and 1 ¾” for 24/20
chambers. If the adjusted air brake chamber stroke is greater than the dimensions listed,
inspect the automatic slack adjuster for wear or damage. See manufacturer’s recommen-
dations for repair or replacement.
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