spring brake problem on the M923A2

[Doug Roberts]

Truck airs up fine , but the spring brakes will not release. One assessment is the prority valve is faulty. What could it be ?

 

[The HUlk]

From what I understand the priority valve on the wet tank will disrupt air from accesories like the horn and wipers. Mine stuck and that was the symptom along with the air not blowing off and constantly building. Took it off and worked some ATF into it by actioning the spring with a small diameter rod.

I would think a failure in the parking brake air circuit may cause the brakes to not release when pressure is good.

 

[Coffey1]

The valve at the parking brake will hang and won't switch and vent the air.

 

[98G]

The valve at the parking brake will hang and won't switch and vent the air.

This...

Use the override on the dash to diagnose this problem. If the dash override fixes it, that's the problem.

Obviously don't use the override as a workaround, only as a diagnostic...

 

[wheelspinner]

You also might just have stuck drums. Block the wheels and get under there with a good size hammer and give them all a good whack. This problem has the same feel as spring brakes not releasing. It's fairly common with wedge brakes if they don't get used a lot.

 

[tractors0130]

Double check that the vent on the front right glad hand (pass. side) is not plugged.Thought my spring brakes were sticking until I found the vent hole in the right glad hand plugged solid. There should not be a valve on this side either. This would be the easiest to do before you check the quick release valve located behind the drivers step or the actual brake wedges.

 

[Hard Head]

Ran into a braking problem last month. Every time I braked, the truck seemed to struggle to pull the slightest hill. 20 miles and I could fry eggs on all 4 rear rims. The vent hole was plugged on the glad hand! I am going to repack bearings before I put it back on the road! One little thing causes a lot of work!

 

[Doug Roberts]

the vent is the glad hand opened ? I'm not grasping exactly where the vent is

 

[tractors0130]

There is vent hole in the glad hand cover on the right front gladhand with a spring loaded vent cap on the outside similar to the vents on your diffs., if the vent is plugged your brakes will start to drag. This vent is suppose to be open allowing air to escape.

 

[Doug Roberts]

thanks , I should have spotted that I think , but it got by me !

 

[Doug Roberts]

there was no vent on the glad hand. Opened it up and the brake is symptom free. Of course we can't leave it open. Maybe the vent is on the frame ? This truck is in another state miles away BTW

 

[MtnSnow]

That is an Improper glad-hand dummy cover for that line.

 

[The HUlk]

Not the first time I have seen somebody find the gladhand vent to be the problem with brake trouble.