Freightliner columbia Brake ((madness))!!

If your trailer brake adj. will not stay adj. then you must replace them with new ones! not many hills that need that much brake pressure, after you replace the brake adj. you will see a lot less air press. needed to get it stopped?

 

If auto slacks won't adjust, they're either shot or the pushrods are cut to the wrong length.

As for air pressure loss when you step on the brakes, have you checked the air loss with the service brakes applied? Park truck, release brakes, push brake pedal to floor and hold it there for a few minutes. Do you lose air or does it hold air pressure? If it holds, you have a supply volume issue (ie water in tanks, tanks too small etc). I believe your reservoirs need to be minimum 7x the volume of all your brake chambers combined.

 

If slacks are failing after only 2 years I'd recommend that they see grease a little more often.

 

Unless your slack adjusters have a release to back them off when adjusting, they don’t like being adjusted. Good rule of a teacher gave me. When the brakes are applied (either park brakes set or a helper applying foot brake) the chambers push rod should be at a 90deg angle to the center of the S-cam shaft (or real close one way or the other). If they break a 90, then they are out and need adjusted. Loose s-cam bushings, wheel bearing torque, and faulty drums can cause s-cams to not hold adjustment. And yes regular grease makes a difference.
Also if your drive brakes are getting low, that can make a big difference on stopping power. And your trailer brakes will work harder to make up for them. (Story time) In my early years, I had a driver who was particularly hard on brakes. At the time, I used the cheapest brakes I could find an reused drums if they looked OK. After his initial complaint of weak brakes, I change all his brake valves, chambers, and slack adjusters because his brake shoes looked fine. I ran all over that truck for a month until I did a drive wheel seal and found the inner part of his shoe was on rivets and the out sides still had a 1/4” more than the DOT line. New brakes and new drums fixed it. Fast forward 10 years, I use the hardest brake I can find, and new (but cheapest) drums every time. Same driver caught me again only this time we found it in the shop. His last set of trailer brakes we had changed to an over sea’s drum to save 10 bucks. Between the hard pad and his habits he belled the cheap drum and was again on the rivets on the inside where it couldn’t readily be seen, If my helper hadn’t notice how high on the s-cam the roller was, he never would have caught it. I’ve learned a thing or two, iwith the brake lining I run, the drum must say “made in the USA”

 

The only problem with the 90 degree angle rule is that it only works if the pushrods are cut to the proper length. The auto slack adjuster is designed to maintain that 90 degree angle. If the pushrod is cut too short, the brake chamber will stroke more to reach that 90 degree angle. If the pushrod is cut too long, it will stroke the chamber less to keep that 90 degree applied angle. If you run the same truck and trailer every day and you know that the pushrod stroke is good at 90 degrees, perfect. If you're always in a different truck or do a lot of drop and hook I would not rely on the 90 degree rule to save your butt. DOT won't care and will probably ticket you.

 

I’m assuming they are automatic adjusters any thing 1997 and newer are supppose to have them.
The only blue ones I’ve seen where haledex. And to be honest I’ve only seen what your describing once or twice. I’m much more familiar with the Bendix (does have a button to pull out and 1/4” square to adjust) and Gunite (7/16 head that ratchets when backed off). If yours are the type I’m thinking, they run up kind of easy, then back off with an increasing drag, those may be finicky about what type of grease is used in them. May not hurt to see if there’s any literature that comes with the new ones. But I’m only guessing, barely an educated one at that....

 

You are correct. The 90 deg trick only works when everything is right. The auto slacks with the adjuster arm mounted to a fixed point are the exception. They readjust based on travel. And the trick wouldn’t work for sure there either.
I forget when I started, most of the units I inherited had mis matched chamber rods and slack adjusters that had been installed by the shade trees before me. Really adjusted my learning curve.

Oh that, if your slacks at failing prematurely, and you have poor brake performance, the chamber rods may be cut to the wrong length. Brakes have there highest application pressure at 90 deg, which is why most adjusters try to hold them there.