M931 Removing Brake Chamber Assembly

[D6c]

I'm trying to remove one of the rear brake chamber assemblies from my M931 and I'm having difficulty getting it loose. I tried using a punch to loosen the lock nut (#10 in the diagram) without success. There's not much room to work on the inside of the brake backing plate.

Before I get too aggressive with it and do some damage I thought I'd ask if anyone has a good technique. Is there a special tool for the lock nut? If the tube was a little heavier I'd put a pipe wrench on it but I'm afraid it would just crush it.
I'ts probably been in place for 30 years so there's likely a little rust.

Thanks

 

[Floridianson]

Yea just rusted PB and a prayer. Why do you feel the need to remove the whole thing? I would also make sure you get the depth correct so if you do get the jam nut loose count the number of turns it takes to get it out.

 

[D6c]

The spring brake diaphragm is leaking pretty good and the plate that the safety bolt hooks into has a piece broken out so it's kind of risky to take it apart and repair. I just bought the whole assembly NOS rather than risk it taking my head off.

 

[Floridianson]

http://www.axletech.com/resources/service_manuals/pdf/MM_4R.pdf Yea understand. I found it and page 17 says to make sure jam nut is out of way and tighten chamber all the way down and not to back off more than one turn to line up air lines. Been awhile had to reread myself.

 

[D6c]

http://www.axletech.com/resources/service_manuals/pdf/MM_4R.pdf Yea understand. I found it and page 17 says to make sure jam nut is out of way and tighten chamber all the way down and not to back off more than one turn to line up air lines. Been awhile had to reread myself.

Thanks for the info....should be helpful.

 

[JohnnyBM931A2]

Fun stuff.. I don't blame you for buying a new assembly rather than taking a risk. Better safe than sorry!

 

[wrenchturner6238]

If you have or can get an air hammer and a blunt punch may help. Air hammers are very good with rusty stuff and if all else use some heat to warm it up some.

 

[Csm Davis]

If you are not reusing it put a big pipe wrench on it and turn, it will break loose and or use a chisel on the nut.

 

[D6c]

I ended up making a split bushing type tool to clamp over the tube on the brake actuator. I cut wrench flats on the tool for a 2" wrench and it loosened it right up.
On one end of my tool I cut teeth to engage the lock nut when tightening down the new part. Didn't have time just now to post a pic but I'll do it later.
The tool worked great so that problem is solved.

Now for the bad news.....got it all back together and the brake won't release on that wheel. Air doesn't compress the spring brake on that wheel when the park brake is released. Even when I pull the spring brake back with the release bolt that wheel is still locked. I'm sure I put the lines back in the same locations....I marked them when I took them off and they don't easily line up any other way.

Perhaps I should have function checked the brake assy. before installing it, but it never occurred to me that a new part wouldn't work.

When I removed the old brake assy. the spring & roller assy. that actuates the wedges came out. I cleaned & greased it and put it back.....felt like it went in right.
Is it possible that the spring & roller assy. is out of place and locking the brake?

I'll double check the lines again tomorrow but I'm kind of stumped.

 

[MyothersanM1]

Were the brakes released when you had the air chamber including the wedge (spring & roller assembly) removed from the plunger housing?

 

[Floridianson]

Cage it and see if it releases.

 

[D6c]

This is the split bushing tool I made to remove the stuck brake actuator. It clamps around the tube and has flats cut on the sides for a 2" wrench to turn it loose. The spanner teeth on the end of the tool were used to tighten the new collet nut. No need to clamp the halves together to tighten the nut as the wrench holds the halves together. Didn't use the spanner teeth to loosen the old nut as they were kind of chiseled up. Worked well.




Figured out what the problem was with the brakes.....it was actually two problems.

I had taken care to move the air line fittings from the old unit to the new one, making sure I got them in the same ports. As it turns out the new one has the spring brake ports reversed. That's why the spring brake wasn't releasing with the air.

The other problem was that the brakes were simply adjusted up too tight. I readjusted the brake pads and I'm good.
Because the spring wasn't releasing it fooled me into thinking that that was the source of the problem, but it was only half the problem. Rookie errors.

 

[JohnnyBM931A2]

Very creative tool Glad you found a solution to the problem