DP Brake Job Cost?

Also, if a brake is out of adjustment it will squeal. Very common on big trucks. I'd get a 9/16 box end and a ballpeen hammer, get under there and tap the boxend of your wrench onto the nut, this will collapse the lockring and allow you to adjust the brake. Turn it unitl its tight and back it off 1/4 turn. This will allow it to rub but won't hurt it. Then back off until the lockring pops back up. It takes 3 minutes to do a single axle and Freightliner will charge you $75.00. Inspect the pad and see what the thickness is. If you don't know what it should be look it up on the internet.
https://www.bing.com/videos/search?q=adjusting+slack+adjusters&FORM=VIRE2#v