Spring Brakes Not releasing

[TCD]

Spring Brakes Not releasing

Hi Folks,

My truck is a 1990 BMY 923-a2 that generally is in very good shape. Unfortunately my trucks sits more than it should. A few weeks ago I went to drive the truck and it would only move when a great deal of power was applied.

A friend solved a problem similar to mine by cleaning and lubing the handbrake valve. I always got the “crying loon” sound when setting the brake but I went ahead and cleaned and lubed the handbrake valve. The problem persists.

I have followed several links on this forum and I have not been able to get the brakes released.

Links I have used so far are:

https://www.steelsoldiers.com/threads/m931a2-rear-brakes-wont-release.176453/#post-2106859 - An excellent document for checking the “Spring air tank” and the related valving.

https://www.steelsoldiers.com/threads/m923a2-brake-issue-help-advice-needed.130835/ - A discussion relating to the handbrake valve.

I have confirmed that I have air in my spring brake tank and both valves tested OK.

When I hit the override valve in the dash I hear air moving and it seemed to make a small difference in the rolling resistance. However the brakes are still locked up even when I get 90 pounds of operating pressure.

During my last test drive the truck was able to move with less power so I drove around the yard for a few minutes. I can't explain this improvement but I suspect one or more spring brakes released. On the rear axles, every drum had a different degree of heat from way to hot to touch to cold. The override valve did not change the brakes during this test.

Next I tap tap taped all of the rear hubs and drums, let the brakes cool and retested by driving around again.

The condition was the same as the test drive above.

So do I need to disassemble each brake assembly to R&R of does anyone have any other ideas or test I can run?

I imagine that removing the drum with the spring brake set is going to take some effort. Any words of advice on disassembling the locked up drum?

All comments greatly appreciated!


Thanks for taking the time to read this and for the help!
Tom

 

[frank8003]

So jack her up complete and pull all the wheels and drums. Might find the problem.
Fix everything in there.
All military trucks were built to use, not used = it fails.

 

[simp5782]

Check the front service gladhand to ensure its not clogged from a critter . If clear proceed below. If clogged then clear and recheck.

Open the rear service gladhand and ensure you do not have air coming from it. If yes. Verify the treadle valve is releasing all the way. If no, you need to verify that air is actually going to the spring brakes. Just cause your gauge reads 90lbs doesn't mean the spring tank has 90lbs

You can jack it up and cage the spring chamber and spin the wheel and see if it drags. If no then you have an air problem. If yes then you have a sticking wedge or rust issue

 

[tobyS]

I can't reply to why this is happening but I think "caging" the brake, will release it. Of course it is entirely inoperable then, but it might give room to get it apart.

 

[frank8003]

brakes

 

[WillWagner]

If these are like OTR stuff, caging might not help. Caging releases the spring pressure. If the shoes are rusted to the drums, chock the wheels, build air, release the brakes and roll under it with a hammer. Smack the drums. If you get a ringing sound, they are free, a thud is stuck or out of adjustment. Smack them a few times, if just rusted, they will break free. Drive it somewhere with no traffic, then re adjust.

 

[TCD]

Hi Folks,

Thanks very much for all of the advice!

I've been traveling but hope to try the suggestions tomorrow or Monday. I have also downloaded the PDF "frank8003" posted and I'll study that document.

I'll report back with any results and/or what I have found...

Thanks again,
Tom