Air over hydraulic brake problem

crzyxj

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I am having issues getting the brakes to work in my 1972 M-35. I replaced the master cylinder and have air pressure, I still have stiff pedal. I must be missing something somewhere. It seems to be pretty simple system. Anyone else have this issue?
 

dmetalmiki

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The problem you are experiencing is most likely with the air pack Which is the 'power assistance' on your trucks braking system.
Try sitting in the cab engine off, NO AIR PRESSURE. press the brake pedal.
Start the engine and build up the air in the system.
Now press the brake pedal.
Any difference?.
 

sandcobra164

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I agree with above prognosis and diagnostic procedure. My Deuce had good brakes but an extremely hard to push brake pedal. My results to the above test felt exactly the same with or without air. Changed my air pack and I could lock the rears without lifting off of the seat and regular braking was much easier than before. I gave my airpack to a member who wanted to take it apart and see how it works. The "air assist" piston was frozen stuck in the bore of the can on the back half of the air pack. That is why alot of people suggest to remove the plug from the back of the air pack and oil the air pack on occasion. One step you might try is to fog some PB Blaster or your favorite penetrating oil into the back half of the air pack. I'm going from memory here and will likely get corrected. I no longer have the truck so I can't walk out to confirm. I know I put a "short" air pack on and don't remember it having the plug to fog the oil into. I believe my older "long" air pack did have the plug on the back side. I'm sure someone knowledgeable will come along and correct or confirm. If you're air pack doesn't have a plug, you can easily drain the air tanks, remove the supply line from the air pack and add oil. Start the truck, allow it to build air pressure and try pumping the brakes. If you get lucky, the assist piston will free up and you won't have to replace your air pack. If I had known that in the past, I would have tried it and maybe got lucky and saved some money.
 

crzyxj

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Yep no change in pedal. I guess I will have to try to lubricate it. Any idea on cost of the air pack or where to get one? I am in the middle of nowhere Wyoming! LOL
 

bigmike

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Airpacks are in the $400.00 range nowadays. There are several suppliers on the internet as well as this site. I think I have some rebuild kits if you are interested.
 

sgms18

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I just put an air pack on my truck & it was a pretty easy job. I can't help ya on the rebuild, I just went ahead & got a new one.
 

crzyxj

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It is not real dirty like I saw on the rebuild thread but the brake fliuid is in there. this truck sat for several years and I am finally getting to work on it. and an axle seal went to **** yesterday! lol. i drove it a quarter mile and well,,, #moneypit
 

pwerwagn

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Not to hijack your thread, but I have a similar problem with my 35a2. I bought it needing brake work. The brake pedal is solid, but it doesn't actuate the brakes.

Is there any work around to have brakes to move the thing?

I also have a spare short airpack, but my truck uses the long airpack. Is one preferred over the other?

If the airpack freezes in the spot that mine must be in, is there a way to get brakes, even if not assisted, to move the truck? My truck is ~130 miles from me, heading down there tonight to mess with it. I gotta get it out of the place its at so I can get it on my trailer to haul it home.

--Jeff
 
Last edited:

98G

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Is there any work around to have brakes to move the thing?



I gotta get it out of the place its at so I can get it on my trailer to haul it home.

--Jeff
Brakes enough to get it on a trailer? The parking brake combined with low range and shut off the engine when it's where you want it.

Brakes enough to drive it on the road? No...
 

pwerwagn

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Brakes enough to get it on a trailer? The parking brake combined with low range and shut off the engine when it's where you want it.

Brakes enough to drive it on the road? No...
That was kind of my plan if I cant figure out the full problem. The parking brake is pretty much non-functional right now, but I did not check adjustment or anything.
 

crzyxj

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Pretty easy to adjust the park brake. Just screv it tight at the handle or the band on the rear output of the tcase. That is how I got mine home, Low range and park brake lol. Was a little sketchy!
 

73m819

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When you are going to lube the air pack, use air tool oil because other stuff may be NOT compatible with the internal O-rings
 

WillWagner

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And, if you rebuild the air pack, lay the parts out as you disassemble, SOME of the TMs are wrong, I had one that was wrong and 1 correct
 
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