Brakes won't release

[Daytodog]

I have a 923A2, problem is the brakes are not releasing sometimes. I'll try and explain as much as I can about what and when it does it and hopefully someone can point me to a link, manual page, or give me some guidance to troubleshoot.
First time it happened was this winter when I went and pulled out my buddies dump truck that he had gotten stuck. I was in and out of the truck hooking up Backing up setting the parking brake etc. I went to pull forward and all the rear brakes were locked. Tried the spring brake release with no luck. Came back a few days later and had no trouble, and pulled his truck out like it didn't even know it was pulling something. figured something had frozen in line.
I haven't been driving the truck much lately due to working on the dump bed I'm mounting on it. So I go to pull the truck out of the shop the other day and the brakes were locked up again. Tried the spring break release Knob again with no luck.
Truck builds air pressure fine parking brake engages holds fine and vents through the exhaust with that goose sound or however you want to describe it. Push the spring release knob in they release. At this point if you use the brakes, which as much fun as it is to run over stuff you need eventually the brakes won't release. Press the spring break knob in when this happens and brakes won't release. Try setting the parking brake and of course no goose sound venting out the exhaust now. Wait awhile (I waited about 2 hrs) start it back up and they will release briefly then lock up again. Thinking maybe it was the valve at the parking brake handle base so I cracked the air lines and operated the switch with my finger and it seemed to be working based on the air hissing from the respective line as you move the lever. So I got back in the manuals and started reading what I thought might be relevant but haven't found what I'm looking for yet. Tried searching past post no luck yet.
Ill say airbrakes are not my strong point but am not afraid to admit that, just explain it to me in detail if you have suggestions, like your trying to describe it to your mom, pictures are worth a lot, when your learning, lol. As always thanks in advance for the help. Here's a picture of the bed finally mounted and the cab controls.

 

[deuceman51]

Does your front glad hand have a breather on it? If not, your brakes will build backpressure and lock up.

 

[Daytodog]

Where would the breather your referring to be located make sure I'm checking the correct thing

 

[Trailboss]

The passenger side front gladhand behind the bumper should have NO valve in the piping, and the gladhand cover should have a little bobblehead vent that the cover on the driver side gladhand does not have.

 

[Daytodog]

Thanks a lot on the road working this week I'll check it out Saturday when I'm home.

 

[mcmullag]

Are you moving the transfer case from hi to low at all?
If the button on the that lever is not all the way out, the truck will not move forward.

 

[Daytodog]

No I haven't been but I'll doublecheck just to make sure the switch is not stuck

 

[Daytodog]

Trailboss checked this weekend and no valve behind glad hand, forgot to check bobble headvent will check again this weekend. Drove the truck around some this week. No issues when using foot brake and even engaged the parking brake several times couldn't get it to duplicate the problem again. Seems to only happen when I use the parking brake, just randomly. Somebody said that if you don't drain the air tanks in the proper order that can cause problems. Not saying they are wrong just not sure how that would create the issue that I am having with the brakes.

 

[Coffey1]

Just taking the air line off that valve at parking brake does nothing.
Take lines off and get some air gun oil in that valve it may be sticking.

 

[Daytodog]

Coffey1 did squirt some air tool oil in the air lines thinking it would push into the valve. I'll try this weekend taking the valve off completely and putting air tool oil directly in the valve, see it that helps. Thought about just replacing the valve at the parking brake if the oil doesn't help. Not sure though what the valve would cost and where to get it at, pretty sure somebody sells it. Haven't tried searching the Internet for it yet.

 

[quickfarms]

You could have one of several issues. It could be in the air system or it could be mechanical.

 

[Daytodog]

Correct you are, suggestions as to the steps one might take to determine the problem would greatly be appreciated. Remember air brakes are not my strong point but I'm learning so explain in details, thanks a lot.

 

[Coffey1]

Start with that valve it's easy to do.
Then it might be wheel and hub pulling time to clean and service all the hubs.
Everything in a brake system is suppose to move freely and these trucks sit for long periods of time things can get rusty in the hubs.and not move like they should.

 

[swbradley1]

I'm surprised someone didn't give you the answer to your first question, a pointer to the manuals.


At the top of the SS page you will see Forum.

Navigate to:
Forum - Technical Manuals - 5-ton and up TMs - TMs for M939 Series Trucks

or a link:


http://www.steelsoldiers.com/showthread.php?121487-TMs-for-M939-Series-Trucks

There is a troubleshooting section table of contents in this one:

TM 9-2320-272-23-1

 

[Coffey1]

Yes Steve you are correct we should have.

 

[Daytodog]

Thanks to everyone for the replies. Working on the road and not being able to run out and check things you guys suggest until the weekend stinks but I guess that problem is for another post. Reading through the manuals you all suggested I had a random thought and wasn't sure so I thought I would ask. When setting the parking break the sound of venting air I hear from the intake behind the cab on the driver side( I say more like a sick duck) is that normal or not? Is it possible that the foot brake treadle valve would be bad causing the problem with the sticking brakes after using the parking brake or would this have nothing to do with the problem I'm chasing?

 

[Coffey1]

Yes it sounds like a sick goose lol.
Anything is possible.

 

[4XDesign]

I had an issue with front brakes not releasing on m925a2 it was a bad check valve under radiator. They can cause issues on rear as well. When I took it apart it was apparent that was bad.

 

[Daytodog]

I'll check it out, but it's the back brakes that are locking up. Of course since I've posted this haven't had any trouble since.