M35A2 intermittent brake issues

[Sam varano]

I have a m35a2 that I have completely stripped and rebuild and I have a brake issue I can't seem to figure out. My issue is intermittently without warning I have a rock hard pedal with no brakes. Everything has been gone through, I rebuild the air pack. I have even torn the air pack apart 2 additional times now. The initial rebuild everything was honed and lubricated with silicone brake fluid on the brake side and air tool oil on the air side. I replaced the master cylinder also during the restoration. The brake lines, wheel cylinders and shoes are all new and properly adjusted and bleed. When the brakes work they work great. I am very mechanically inclined and even did my own HF54 power steering conversion but this is driving me crazy and I am at a loss.

 

[silverstate55]

This happened to me on my Deuce several years ago, and it involved a small piece of something blocking the small relief (pinhole) in the master cylinder. I managed to get a welding torch tip cleaner into it to clear the blockage, but had to remove everything & flush the lines later to make sure it didn’t happen again.

 

[davidb56]

This happened to me on my Deuce several years ago, and it involved a small piece of something blocking the small relief (pinhole) in the master cylinder. I managed to get a welding torch tip cleaner into it to clear the blockage, but had to remove everything & flush the lines later to make sure it didn’t happen again.

It sounded like a master cylinder problem to me also, but I don't know enough about the air assist to determine if they can hold pressure on the master cylinder instead of assisting it.

 

[hoop]

Clean the small relief hole.

 

[Sam varano]

Ok so today I pulled the cap off the master and sucked out most the fluid so I could see the small return. I could see fluid squirt from it briefly when you first applied pressure to the pedal and then a lot of fluid once the pedal was released. I went ahead and pulled the master cylinder off and disassembled it and saw nothing wrong with it. Keeping in mind this was a NOS cylinder so I went ahead and reassembled and bleed the whole truck again. The problem is still there. The more I play with it the more I do not trust this system. I mostly use this truck to haul everyone around at my camp which is in the mountains of Pennsylvania. As you could imagine brakes are pretty important. Has anyone converted over to a disc brake setup using a hydraulic booster? I do have a power steering conversion. If I am able to figure out what's wrong with the stock system I am at the very least adding pinion brakes to the front and rear differential for a backup. Thanks again for the suggestions

 

[davidb56]

There should be some info on adding a hydrovac booster and master cylinder, which would split the rear and front brakes hydraulically, making it like a regular truck. No need to convert to disc unless you want to. Since you have a power steering pump, this should be a easier job. You also have to change the brake pedal mechanism so it "hangs" from under the dash by a firewall mounted bracket. Maybe "Hanks Deuce" website has some info. I don't like going there because it makes me want to spend $$$ on upgrades he has done.

 

[Sam varano]

There should be some info on adding a hydrovac booster and master cylinder, which would split the rear and front brakes hydraulically, making it like a regular truck. No need to convert to disc unless you want to. Since you have a power steering pump, this should be a easier job. You also have to change the brake pedal mechanism so it "hangs" from under the dash by a firewall mounted bracket. Maybe "Hanks Deuce" website has some info. I don't like going there because it makes me want to spend $$$ on upgrades he has done.

Honestly I think you just gave the best advice, there is really nothing to fabricating a bracket and pedal and the rest I can go pull from a salvage yard. Couple hundred dollars and a much safer brake system.

 

[hoop]

Can you see both holes working? As in releasing fluid...

 

[hoop]

If you look at the 3rd pic on post 23 you can see both holes. and the size difference. https://www.steelsoldiers.com/threads/brake-not-bleeding-off-pressure.185079/page-2#post-2256244

 

[Sam varano]

If you look at the 3rd pic on post 23 you can see both holes. and the size difference. https://www.steelsoldiers.com/threads/brake-not-bleeding-off-pressure.185079/page-2#post-2256244

I really didn't pay any mind to the larger hole to the front to notice if anything came out of it, I was only really paying attention to the smaller pin hole to the rear. Does fluid release from that one also, if so I don't think it was I would think it would have caught my attention

 

[hoop]

Yes.

 

[Sam varano]

Yes.

That may be my issue then, I know the smaller rear hole was returning the fluid under what I thought to be extreme pressure. After I drained down the master cylinder there was less than a half inch of fluid left and it was able to squirt it up and out of the reservoir

 

[bigmike]

My experience is that the little hole getting clogged creates a lockup of the brakes until fluid is released Not the opposite.

 

[hoop]

Bigmike is right. But I remember most of the pressure coming from the big hole. I can go out and check tomorrow....
My remembering skills are not what they used to be.....