Brakes Won't Release After First Application

[lilymonster]

I've looked around here and searched a fair amount and did not see any threads describing a problem I'm having with my M35A3. Basically what's going on is the first time I apply my brakes after starting the truck up, all 4 rear wheels stayed LOCKED. Now, I can get them to release, but only by shutting the truck off and purging the air out of the system. Once the pressure bleeds down, then the brakes will let up and I can then roll the rear tires again. I lifted up the whole back end to do this test. Any ideas here what's going on here??? Is there a valve or something somewhere that is sticking? Please let me know if you have any ideas, THANKS! I'm have owned other military trucks, but I am new to the Deuce, especially the M35A3

 

[porkysplace]

Airpack is probably sticking
MY Airpack Rebuild with Photos!

 

[flyxpl]

I have had this happen with air and dirt in the master cylinder also . I am taking a guess if it was the airpack all 3 axles would be locked up . Look into the part of the master that runs the rear axle .
I have had rust in the compensation port cause this problem .

 

[FormerNewMVGuy]

Airpack is probably sticking
MY Airpack Rebuild with Photos!

Doesnt That have dual airpacks?, Not being smarta$$ , Just wondering?
i thought they had the dual circuit system.

 

[porkysplace]

Doesnt That have dual airpacks?, Not being smarta$$ , Just wondering?
i thought they had the dual circuit system.

It should have duel airpacks , since only the back brakes are locking ,it's most likely the airpack for the rear or the master cylinder

Edit ; It looks like it does only have 1 airpack with a duel port master cylinder and proportioning valve .
This attachment may or may not help .

 

[flyxpl]

I was under the impression one airpack with two resivoirs . I only see one airpack on my truck ??

 

[johnejones]

had similar issues on my truck....after much wrenching I found that the 1st piston in the 2 piston Master was not releasing completely and would not let the fluid release. In addition, the actuator rod was falling out of its socket when this happened and would always keep pressure on the pistons. It will be rebuilt but I was able to secure replacement from other member and it works great now.

Note....when done adjust brake shoes first as if not you might think you are not done bleeding the system when you are......I have the empty bottles of DOT 5 to show what happens when done backwards.

On mine there is 2 airpacks not close to each other and my understanding is that one is for the front and one for the back. that being said, I sell fish for a living and only ticker with trucks so if someone with more experience tells you different you might listen to them

JJ

www.lochowranch.com

 

[gungearz]

I'd bleed them first before tearing anything apart. Its still possible to have something lodged somewhere in that main line for that tandem.

 

[gimpyrobb]

Do a search for "compensation port".

 

[steelandcanvas]

Mactiredearg and I are going to rebuild (2) airpacs on his M35A4 this weekend. Same scenario, except all wheels locked up. We were able to release the brakes by opening the bleeder screw in the M/C, but as soon as you touch the brake pedal, it locks up again. Something's not releasing somewhere.

 

[mactiredearg]

My M109A4's symptoms are slightly different. The brakes do lock up, but not immediately. They get more and more locked with each press of the brakes until they are completely locked. Takes 5-6 pumps to get the full lockup. Also the front brakes seem more locked but that may be due to brake adjustments.

Then draining the air tanks does nothing. The brakes stay locked up until I get underneath and loosen up the bleeder valves on BOTH master cylinders. However just running the engine and building up air seems to have caused the block without the brake pedal being pressed, but I have to confirm this.

Our current thought is flush the brake fluid and if that doesnt resolve the issue then move on to an airpack rebuild. Anyone have suggestions.

 

[1 Patriot-of-many]

Doesnt That have dual airpacks?, Not being smarta$$ , Just wondering?
i thought they had the dual circuit system.

Yes they do. The left one has the brake light switch on it, the right one doesn't. I couldn't tell you which pack is for which circuit, but they can easily be traced.

Should be fairly easy to determine which airpack is kaput by which wheels are locking up if thats the problem. Didn't someone have a plugged vent on the MC that was causing the same issue?

http://www.steelsoldiers.com/deuce/73202-help-brakes-stuck.html

 

[1 Patriot-of-many]

It should have duel airpacks , since only the back brakes are locking ,it's most likely the airpack for the rear or the master cylinder

Edit ; It looks like it does only have 1 airpack with a duel port master cylinder and proportioning valve .
This attachment may or may not help .

Mine has two airpacks. One is on the right side of the vehicle behind the battery box, one is on the left side with the brake light switch mounted on the front of it.

 

[jrv7874]

My M109A4's symptoms are slightly different. The brakes do lock up, but not immediately. They get more and more locked with each press of the brakes until they are completely locked. Takes 5-6 pumps to get the full lockup. Also the front brakes seem more locked but that may be due to brake adjustments.

Then draining the air tanks does nothing. The brakes stay locked up until I get underneath and loosen up the bleeder valves on BOTH master cylinders. However just running the engine and building up air seems to have caused the block without the brake pedal being pressed, but I have to confirm this.

Our current thought is flush the brake fluid and if that doesnt resolve the issue then move on to an airpack rebuild. Anyone have suggestions.

I had the exact same symptoms when I picked my A3 up from Ft. Drum. It turned out that the brake pedal arm under the floor was hitting the floor when released. So the pedal was never getting fully released. A quick adjustment and everything was all better

 

[mactiredearg]

Update: Went over to steelandcanvas' shop Sunday morning and we got back to work on the truck. Pulled the skid plates for the airpacks and then pulled the vent lines. Ran the truck up to pressure and pumped the brakes. The driver side air park was venting correctly, but the passenger side wasnt at all. Shut down and pulled that air pack.

We took the entire thing apart, well as much as we could, but for either of our lives we couldnt see anything wrong. The gaskets look fine, everything seemed like it should. Only thing that seems slightly off kilter was the alignment of one piece in the side stack where the vent elbow connects (I haven't been able to find a diagram with that part of the air pack exploded to say which part). We also could not get the parts in that portion of the air pack out. There was a snap ring to hold them in, but when it was removed they wouldn't budge...

After this tear down we re-greased everything, put it back together, put it back on the truck but left the vent disconnected. When we had it back on the truck and were back up to pressure we tried pumping the brakes again. This time that air pack did vent. Problem is the brakes still gradually locked up with each pump. Only difference besides the venting is that the brake pedal did not go to full lock where it would not budge at all. Now there was an inch or so of play still left in the pedal at full lockup.

After this lockup I was able to get the brakes to release by opening the bleeder valve on the passenger side airpack only.

Unless someone has some thoughts on what in that side-stack might cause this issue (and how to get the parts out without breaking them) I think our next course of action is to drain the brake fluid and pull either/both the differential valve and master cylinder and see if a teardown of them revels anything

 

[JH1]

I had this same problem happen on a M813. Different animal, but maybe similar. The field fix on the 800 series is to crack open one of the two towing air ports under the front fender just a little. That will allow the pressure to vent back out, while not affecting the braking markedly. Not a permanent fix, but I know a guy who did that for a year with no problems. Fix asap, of course. This is just to get you off the road, around the corner or home, it is really close.

 

[lilymonster]

OK, so I believe I have narrowed it down to the drivers side air pack, which is the one that works the rear wheels. My question is: WHERE is the best place to buy one of these either new or used for a reasonable price? Does it matter what version ("new" or "old") I buy? I don't have the equipment necessary here to rebuild my own that is why I am looking to buy a cheap USED, rebuilt, or new one. Anyone have any ideas where to get one for the best price? or possibly have a used one they would part with? I'm just looking to do this as cost effectively as possible. Money is tight right now.

 

[steelandcanvas]

OK, so I believe I have narrowed it down to the drivers side air pack, which is the one that works the rear wheels. My question is: WHERE is the best place to buy one of these either new or used for a reasonable price? Does it matter what version ("new" or "old") I buy? I don't have the equipment necessary here to rebuild my own that is why I am looking to buy a cheap USED, rebuilt, or new one. Anyone have any ideas where to get one for the best price? or possibly have a used one they would part with? I'm just looking to do this as cost effectively as possible. Money is tight right now.

Basic hand tools and a pair of snap-ring pliers will get you apart and back together again. Here is a link for the rebuild kit:


Rebuild kit for the M35 Truck Air Pack, 8345007

 

[FormerNewMVGuy]

Basic hand tools and a pair of snap-ring pliers will get you apart and back together again. Here is a link for the rebuild kit:


Rebuild kit for the M35 Truck Air Pack, 8345007

I would assume he has the new style airpacks on an A3, Do the kits fit both the long (old) and the new?

 

[1 Patriot-of-many]

Call or email Erik. Great guy to deal with, he would probably know.