How Do You Check and Adjust Air Brakes?
Checking your air brake adjustment from time to time is a good idea, everything after 94 has automatic slack adjusters which cannot be replaced by the manual adjust type. After some years of service, the automatic slack adjuster may lose its alignment due to brake cans being changed, or can or cam brackets being bent, heavy or no grease, missing adjuster pins, any of these things can affect the performance of the slack adjuster.
If after correcting any defects and the adjustment changes again, replace the slack adjusters, always do both on an axle at a time to ensure proper vehicle control while braking. There are a few different automatic slack adjusters being used on trucks today, some of the tools you may need to check your brake adjustment are 7/16, 9/16 socket and ratchet or wrenches, 5/16 pipe plug socket, small flat blade screwdriver.
Before starting your brake adjustment make sure your air system has 120psi, with the engine off, block two sets of wheels front and back, (don’t rely on shutting the truck off in gear if the engine compression is low the truck will move, resulting in injury) then release the parking brakes, get your tools and a good work light and begin your brake adjustment on your manual or automatic slack adjusters.
If your automatic slack adjuster has the hex adjuster just run the adjustment up against the drum lightly and back off 1/2 turn, make sure to watch the cam when backing off, if the cam doesn’t move right away because of slack adjuster wear you will have to increase your back off amount, and/or replace the slack adjuster.
If your automatic slack adjuster has the square adjuster run the adjustment up against the drum lightly and then find the release button on the slack, insert the flat tip screwdriver under the button and rotate it to pull the release button out, then back the slack off 1/2 turn, again watch the cam movement, increase or replace if cam doesn’t move right away.
If you have a manual slack adjuster use a 9/16 wrench and push in on the release cone and turn the adjustment up against the drum lightly and back off 1/2 turn, again watch the cam movement, increase or replace if cam doesn’t move right away. Also, make sure the release cone pops back out or the adjustment will not stay if it won’t come out, replace the slack.
Most manual and automatic slacks are adjusted clockwise, but it’s a good idea to have a work light present and watch the cam direction, you want the cam to be moving the same way as the brake can stroke. Often you see the manual type adjusted backward making the adjustment worse than before or no change at all, just poor braking.