XM211 Air Pack - need Help

Hi all. I hope you have your smarts caps on.
I have this XM211 that I have to get out tomorrow or I am in big trouble.

I have managed to restore this beast to the point where it runs well, lights all work, etc.
but I have this one problem. If I have air preassure going to the air pack, then all of the brakes
lock up harder that a w___es heart.

I will only have a few hours in the morning to tackle this. Are there any tricks to clearing
problems with these air packs, short of removing it and rebuilding it.

I really don't want to drive this without the air assisted brakes. There is an M108 wrecker body on the back of this truck and it weighs a whole bunch.

That happened to me on my Deuce a couple of times before I pulled the airpack for a good cleaning. I think what is happening is that the large plunger in the airpack is sticking so that there is continuous boost to the hydraulic side locking the brakes. First time it happened to me when I stopped at a store, I shut down, bled all the air from the system, shot some lube in the plug at the back of the airpack, banged on it etc. until it freed up which released the brakes. Until I had time to pull the pack, I used downshifting and gentle application of the brakes to try to prevent it from locking again.
Good luck with it

As a addendum to my post, I might suggest that for this situation, instead of using pneumatic tool oil which is recommended, you might try something a little thinner with a long spray nozzle so that it will allow you to spray into the hole and apply it to the top and sides of the cannister better. Then maybe some tool oil that will mix with the thin stuff and get you home. This is the approach I would take. You might wait for some more ideas here, but I think you have to get that plunger moving somehow.

How difficult is it to pull and overhaul the air pack?
Thanks a bunch for the the tips on freeing it up!

Bruce, as for rebuilding, see MVM article in June 2002 issue #91.

To confirm that the air is released, open the gladhand on the driver's side at rear of vehicle. The air pressure at this connection is the same as what's applied to the large piston within the airpak.
If it's not being vented then the valves in the airpak "control assembly" are sticking or the vent tube is clogged.

Air pak rebuild

Rebuild kits for the M211 Bendix air paks are N/A (or at least I could never find one). The 5 ton M54 / 800 trucks use a larger Bendix air pak than the M211, but 95% of the rebuild kit works for the M211 / M135. There is one seal for the small piston on the top of the M211 air pak that can not be used from the 5 ton kit. You can find the kits on Ebay for around $25. Beware of the Gov rebuilt M211 air paks that show up every now and than, evey one I puchased (three of them) was junk and needed rebuilt.
Good luck, Karl

RE: Air pak rebuild

Mico lock...is the electric valve which holds hydraulic pressure and the switch is marked "do not use for parking" as it eventually pushes fluid thru the weakest cup in the system... and in the M211 series there are 24 cups in the wheel cyls plus those in the MC and PaK......ACE

What is the NSN for the air pack repair kits for these trucks? Is it 2530-741-0844? The box also has DA-20-113-AMC-10581T C=10/66. Just curious if this is the kit for the air pack.
Thanks Marti

First off, Thanks to everyone who replied!!!
I had already disconnected the mico lock.
To test where the problem was I merely opened up the drains on the air tanks,
and voila, the wheels would turn.
I tried to pull the air pack off to see if I could free up things, but due to the modifications
when they added the M108 wrecker body, I couldn't get the wrenches that I have to
fit in where I could remove the air line nuts.
So we ended up just not using the air pack. The Brakes work ok if you are not
going too fast. Remember, the M108 wrecker body is not exactly light weight.

Needless to say, it was an exciting time had by all.
I will post a detailed report when I recover in a few days.