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M35A2C master cylinder failure?

DeucesWild11

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Isn't that what it looks like in the TM?

Air blowing out the vent is classic bad air pack. (which one?, you'll need to remove the vent lines and see which one).

I'd rebuild both, and the master cylinder.
Ditto on what DH said, I would do the same. I don't have the same set up as you but I had a bad airpack and MC with brake fluid blowing out the vent tube. Knowing what I do now, I would do all in your case. If one is bad the other could be right behind it. With trucks this big brakes are a good thing!!

If you do it yourself the cost is relatively cheap for the safety and piece of mind!:wink:
 

oifvet

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Just so I understand correctly...

If there is no air built-up in the system, (system bled / air tanks drained, truck sitting...), and pushing on the brake pedal with the pedal going to the floor with NO resistance, the DOT 5 from the master cylinder reservior is squirting out of the open end of the vent line located in the engine compartment firewall, this could be at least one bad air-pack?

I believe the air-pack rebuild kits are easy enough to find... The MC is another story.
 

gringeltaube

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I don't see how this could be caused by the airpack, with no air pressure left.
But I could imagine a malfunctioning MC, with the reservoir(s) topped off and spitting out some excess fluid via that vent line, when the pedal is pushed all the way down.

G.
 

lawdog1623

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well i guess i'll add these two rebuilts to the "stuff i will do now but didnt know i needed to do before a catastrophe happens" list.
 

G-Force

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I would get yourself a set of line fittings the size of the ones that screw into the master cylinder with some short lengths of tubing that you can put a flare on the same as are on your existing lines. Crimp or have the line ends welded and screw them into the connections on the master cylinder and then pump the brake petal. If you still have brake fluid blowing back into the reservoir and out the vent then this proves there is a master cylinder problem. If you are able to build pressure then I would look elsewhere. Either the air packs or even the pressure differential switch for the brake light on the dash.
As for the M35a3c master, you could use that with your existing reservoir I believe. you will just have to get the fittings and the adapter plate to mount the reservoir remotely like on the a3 (better setup in my opinion). your existing reservoir bolts onto the top of the master. When I was researching this a while back the A2 master was obsolete but the A3 was still available but not the remote reservoir or the adapter plate.
At least you have something interesting to do today!!!!:grd:
 
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oifvet

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As my pre-MC removal ponderings continue, even in my sleep, I went outside this morning (before coffee) and put the cardboard down and crawled back underneath to look. This time, I brought the end of the vent line down to where I was and held it in a rag and operated the brake pedal arm again. The fluid did not pump out right away. It took several operations of the brake to get fluid to travel out the vent line.

The MC is obviously developing some hydraulic pressure. I know it is minute, but it's happening somewhat.

I hate to start throwing parts at this problem. I suppose removing the MC tomorrow will be a start. The MC that I found in another thread (and posted on page 2 of this thread) has me curious. Either that, or order the M35A3 master cylinder from TNJ Murray (or somewhere) and run the lines to a remote reservior and create the M35A3 arrangement on my 1989 USAF M35A2C.

The PITA factor is climbing. Maybe I'll just overreact and head to the classifieds. That's been my coping mechanism many times in the past.

I'll ask this...

If one (or both) airpack(s) fail, how do they fail (usually)? Would they indroduce air into the system to the point where these symptoms would exist? Would the airpack mechanism "collapse" to the point where they no longer pushed out to the wheel cylinders? In other words, the airpack now absorbs all of the hydraulic/mechanical movement of the system. Does and airpack "blow" catastrophically? Would this truck make a better range target than a hobby? (PTSD kicking in).
 
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groundog

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:grd:I JUST RE-PLACED THE MC ON MY M-813A1---I USE A WRENCH DESIGNED FOR USE ON STARTERS---IT IS CURVED---HELPS GET TO BOLT #4---ALSO USE A SHORT RACHET---GOOD LUCK ON YOUR BRAKES---I RE-PLACED ALL WHEEL CYLINDERS---RUBBER HOSES AND THE AIR-PAK---BRAKES ARE VERY IMPORTANT
 

73m819

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Memphis Equipment has the late model USAF dual MC's for sale.
They will also charge you for the M/C about what you paid for the whole truck, , my truck will sit and turn to dust before a M E part goes on it.

Eastern Surplus also has the M/C
 
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oifvet

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I began the MC removal today. Everything went pretty smooth. I used a turkey baster to empty the reservoir. The DOT 5 was clean. There was not any rust or sediment. I removed the lines from the side of the MC w/o any difficullty.

Before I started to remove the four mounting bolts (last step), I pulled on the brake pedal arm once again just to "see". I held a rag next to the port closest to the front of the truck and fluid shot out like no tomorrow. The second port did the same on another pump.

I'm all for taking the MC down and inspecting/cleaning, but I'm wondering if a good pressure bleeding of all fluid in all lines would be worth doing first. I know the DOT 5 is expensive, that is not my concern right now.

One thing that I recall from the other day when the brakes stopped (well, not really "stopped"), but "quit working", was a noise that I heard. Thetruck is obviously loud, but I thought it was something that fell inside the cab near my seat, like a padlock or something. I thought it might have even been something inside the toolbox area under the driver's seat. Now I'm thinking that the one air pack is under the frame rail on the driver's side. Might that pack have been frozen and "let go" all of the sudden, thus causing a sudden noise and ejecting fluid back through the MC and reservoir? I realize now that it was brake fluid under the engine hood that shot out of the vent line. I originally thought it was from me pushing on the pedal, but now I'm not convinced of that either. I'm just doing some brainstorming/mental troubleshooting before I start tearing things apart and buying expensive parts that might not be the problem. Thought it best to think first, and try not to turn this into something expensive and maybe unnecessary.

What might be the symptom of what I described? (An air pack that was stuck, suddenly "popping", if something like that even occurs?)

Thanks in advance (again) for any and all useful information regarding this phenomenon.

*********************************************************************************************

I removed and thoroughly claened the MC with isopropyl alcohol. There was no rust or pitting and the seals were beautiful. There was crud that might have been bloking the check valves beloe the reservoir. It seems to work. It shot fluid across the driveway.

The MC was reinstalled without much difficulty or swearing.

I purchased a Motive Power Bleeder but cannot get fluid to push through the system. I cannot develop any pedal pressure. Only a small amount of "old" fluid pushed out before everything stopped. No fluid pushing through.

I will try again tomorrow and see what I'm doing wrong.
 
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oifvet

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Have you figured out what the problem is oifvet???
Though I cannot point to anything and say, "this was the problem", I believe the check valves in the bottom of the master cylinder were blocked open with debris and crud.

I removed and cleaned the master cylinder without much headache. I then bed the system thoroughly and replaced the old fluid with new (DOT 5). A lot of crud and goo came out (with the air bubbles), and I now have great brakes.

One thing I noticed... I had to use a second person to pump the brake pedal AND use the power bleeder to push the fluid! I could have used a vacuum pump bleeder at the fittings to get things moving faster. I don't know why, but the power bleeder would not push through the master cylinder and the rest of the system without the pedal being operated. Maybe the design of the MC or the dual circuits, but it took longer than I expected.

I have solid pedal and good braking now.

What a relief!

I'm back on the road, and much more cautious! :driver:
 

oifvet

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I used the Motive Power Bleeder (garden sprayer type) with the tree-tab twist-lock adaptor (proper for reservoir w/ 1.68" ID cap size, a.k.a. "Chrysler"), and even though they advise "10 p.s.i.", I took it up to 25 p.s.i. and prayed I didn't spit the reservoir. The pressure on the system kept everything topped off so I did not have to keep checking the level of the reservoir. It just didn't keep the steady flow like I have seen on the original "single circuit" system on my 1971 M35A2. I got the job done, but it was not as easy as I had anticipated.

Whoever decided to use a two-cap plastic reservoir and locate it beneath the cross-member and right below the driver's (often dirt covered) floor needed to give their parent's money back from sending him to engineering school at some expensive college. Mom and dad did NOT get their moneys worth out of Jr.'s education. I'm sure he partied and cheered the footbal team on, but I cussed him good when I was under that truck. Not that it is essential, but one cannot even access the second cap. It is completely obstructed.
 

gringeltaube

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Well, guess he meant the one who decided to use THAT master cylinder for THAT application...

Obviously referred "Junior" grew up; realized that his creation wasn't that user-friendly and only a few years later came up with the remote reservoir, in the M35A3...;-)

Oifvet: glad you solved your problem, for now at least.
Since everything looked new, have you considered retrofitting your MC with a remote reservoir?

G.
 

3dAngus

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This just arrived in todays mail. Came from TJn murray and won on a popular web auction site. Cost? $50 plus shipping. Thanks to this thread for citing the need for a backup spare in my spares kit. Also received two toolboxes from a SS member where I can store many of my backup spares in the lockable tool boxes which will be mounted in back of my bobbed deuce.

This one is listed for dropside cargo truck 2 1/2 ton,
TRUCK, CARGO, DROPSIDE 2 1/2-TON 6X6 W/E
and is NSN 2530-00-753-9267

I hope it is the same form fit and function as the M35A2. It is new, old stock, produced in Sept, 2006.
 

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3dAngus

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He advertised it for a M35A2. Do I need a dual? I don't have my deuce here where I can compare this vs. the one currently installed.

Never mind, TM indicates its the same NSN. Thanks. I'll still compare it to my deuce to see if there is any difference. Not sure what the dual does vs the single, but I'll find out.
 
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