One service brake won’t release...

[ppillard]

Hi all. First post here. I’m limping my newly acquired ‘97 M1078 from Michigan to Dallas, TX.
My mechanical background: Back in the day, I was a diesel mechanic on semi’s and construction heavy equipment.

When I inspected her and decided to buy from an individual (in Michigan), she seemed pretty solid and was in service as a log hauler until recently.
An hour into the trip home, the water pump failed. Had her replaced at a local shop.
2 hours into the next attempt, when I got into some traffic, I discovered the service brakes weren’t completely releasing. Furthermore, a temp gun on each drum reveals that the right, rear drum is significantly hotter than the other 3 (260* F vs 200).
I’m about to tear into this RR brake, hoping to find dirt, rust and debris that might inhibit brake release. Can anyone offer any suggestions that might shorten my troubleshooting? I’ve done plenty of work on semi brakes, but these look a bit different.

 

[simp5782]

Hi all. First post here. I’m limping my newly acquired ‘97 M1078 from Michigan to Dallas, TX.
My mechanical background: Back in the day, I was a diesel mechanic on semi’s and construction heavy equipment.

When I inspected her and decided to buy from an individual (in Michigan), she seemed pretty solid and was in service as a log hauler until recently.
An hour into the trip home, the water pump failed. Had her replaced at a local shop.
2 hours into the next attempt, when I got into some traffic, I discovered the service brakes weren’t completely releasing. Furthermore, a temp gun on each drum reveals that the right, rear drum is significantly hotter than the other 3 (260* F vs 200).
I’m about to tear into this RR brake, hoping to find dirt, rust and debris that might inhibit brake release. Can anyone offer any suggestions that might shorten my troubleshooting? I’ve done plenty of work on semi brakes, but these look a bit different.

Cage the brake cans, smack the drum with a hammer. Ensure its released and move on home

 

[ppillard]

I just find one of the rear brake chambers leaking air pretty heavily. I’ll replace and evaluate.

 

[Suprman]

If you have moisture in the air system on a cold day it can freeze and block off the air release system. Have some one step on the brakes see if air is releasing from the front blue gladhand. You should get a puff when the pedal is released.

 

[ppillard]

Cage the brake cans, smack the drum with a hammer. Ensure its released and move on home

This I did. And I capped the air lines going to the chamber. Got me home. Thanks.

 

[fasttruck]

Wedge brakes are less common in the commercial world than s-cam brakes so naturally the Army loaded up on them. In theory they are self adjusting but the military is buying self adjusting slack adjusters for cam brakes too. My M871A2 has them. The wedge brakes, if not operated often or submerged in water have a habit of sticking. As post 2 suggests, beat on it with a heavy hammer to try to release it. Obviously brake has to be released and the truck chocked so it does not roll away.

 

[ppillard]

Next issue: the engine fan is not engaging, and she’s running a bit hot. Is there any way to override the air clutch?

 

[Suprman]

Pull cb22

 

[wandering neurons]

Springs in the spring brake chambers (two per wheel) break and puncture the diaphragm. You push the knob on the dash for the spring brakes, pressure should override the spring in the chamber, pushing the diaphragm and releasing the brake. With the punctured diaphragm, the spring brake will not completely release and cause dragging. Ask me now I know. You can either replace the whole assembly and hope that the springs and diaphragms are good, or carefully and safely disassemble the whole thing and replace broken parts. I did a write-up on this several years ago here.

 

[fasttruck]

Some clutch fans (Hortons I believe) have a provision to pass a bolt through the clutch sides which will cause them to turn as one. Repairing ruptured emergency diaphragms in dual service brake chambers is hazardous to your health when the spring gets away from you. Springs are bigger than those on some cars. See attachment. It is usually prudent to replace the chamber assembly if their is a fault in the emergency side. Service side and single service chambers are repairable. Some manufacturers do not even put a removable clamp on the emergency side to save people from themselves.