dha
The slack adjuster is to keep the brakes adjusted properly. The air chambers that accuate the brakes only have a limited amount of stroke. As the pads wear, the slack adjuster must make up for the wear. All air brakes have an external slack adjuster. I assume you are referring to automatic slack adjusters.
I don't know about the failure rate as a % per year, but they can fail. A common cause is rusting and corrosion from road icemelt chemicals. Some of the new salt replacements can be much more corrosive than salt.
You can tell if the auto-slacks are working by checking the amount of travel in the brake chamber pushrod. The pushrod should move no more than 1 inch when moved by hand. This check must be done with the brakes released. This requires the vehicle to be on a level surface, and please chock the wheels! The human body makes a very poor wheel chock.
Improper slack adjustment is usually listed as the number one reason for out-of-service orders at inspections.
Thanks for the information- very useful.. I was also wondering whether over-braking can force the slack adjuster to open past the specified distance and if so, would this be considered a failure. Also, is there an accepted maintenance schedule or are these maintenance free?
