M35A2 LOTS of Brake questions - HELP!

[Jake0147]

The problem with the OP's brakes can be narrowed down pretty easily. All six brakes didn't fail at once and then recover just as quickly. The trouble is a bound linkage (unlikely but possible) or something related to the airpack. Most likely internal, but not "guaranteeable" until somebody dissects it to see what is on the inside.

AZDeuce, question: When the brake pedal gets hard, if you pinch the seat good and tight and rail down on the pedal with everything you've got, it doesn't move far but does it give you ZERO brakes, or does it give you "just a little bit but completely inadequate" brakes? That might help you narrow down without a doubt if it's a mechanical issue or if it's an airpack (power assist) issue.


All the discussion of brake fluid on this site amazes me. DON'T TRUST YOUR BRAKES TO WHAT SOME GUY ON THE INTERNET SAID!!!

You can mix DOT 3, DOT 4, and DOT 5 at will in a deuce. You can find several of the Army's technical manuals instruct that you mix glycol and silicone fluids. There is no reaction, they don't mix, they just sit there and continue to work fine. Seal compatibility is not an issue in this case. The only case where it could be an issue is going the other way, from a DOT 5 only system and adding glycol. Deuces don't have that. They have hand stenciled warnings sometimes, but that's the required practice. The parts the system is made of both before and after the military switched are designed for glycol, the DOT 5 is a retrofit.
When somebody has a picture of snot in their master cylinder and says that it proves there was a reaction... Put it in an analysis kit and send it to a lab, just like taking an oil sample. You will find that the mixed fluids include more than just those two components.


Anyone who has synthetic brake fluid in their vehicles... Make sure all your seals and gaskets are compatible with that stuff... LOL. All I can say is I hope it was the same price as the regular. It's a recent marketing ploy started by one company, followed by another brand supplied by that company... Just a gimick and no more. ALL current main stream brake fluids (DOT 3, DOT 4, DOT 5 and DOT 5,1 ) are, always have been, always will be, and by definition can not be anything but "synthetic" in nature, regardless if it says so on the label or not.

Anyone who takes me at my word for any of this deserves what they get... LOL. Really, this is my contribution to you, this paragraph right here. All of this information IS AVAILABLE TO YOU. Nobody is going to hand deliver it to you, because it is not profitable information. Some guy on the internet says two fluids are can not be mixed. Some other guy on the internet says they can be mixed. One says seals are compatible, one says they're not. What do you do? Pick your favorite and hope for the best? Heck no, It's your brakes for goodness sake. Grab a pickle jar and mix up a witches brew with your fluids, see what happens. Bam! First hand knowledge. Look up replacement seal kits for Deuce wheel cylinders, or complete replacement wheel cylinders for that matter. What does the manufacturer say about compatibility? Or if you're really ambitious, just find the material and investigate it's compatibility yourself.

 

[jeffhuey1n]

Jake, you beat me to the punch line. First off, mixing fluids was beat into my head as a really bad thing. I never worked on trucks, I worked on helicopters. The fluids we used NEVER get mixed. That gives me a knee jerk reaction to always say, don't mix, if you do replace everything. I am learning that the M35 is one very forgiving beast. How forgiving, I've yet to learn.
Bottom line, read the book, they're here on the site. When in doubt, read the book. If that doesn't help, ask which book to read, but Jakes 100% correct, trust only as far as trust has been earned. The books rarely give bad info, especially on a 40 year old truck.

I won't mix my fluids...just can't do it. There's some crew chiefs up in heaven that'd come down and kick my backside for even thinking it.

 

[Recovry4x4]

I agree with Jake here. Like he said, it's possible but unlikely bound linkage. The only other source would be the air pack. Any time I have one that gives me the first bit of problems I switch and rebuild it. Don't play games with brake and the airpack. Wanna read more about what Jake was saying? Go to the TM section and download TB 43-0002-87. It covers BFS conversions. As far as switching from DOT5 to DOT3, countless FD's did this to their FEPP deuces and many on this site have. One that everyone knows is Cranetruck. Did this 10 years ago or better, he's still trucking right along. Go forth, gather info and learn!

 

[StreetbikeDepot]

I use DOT 3 in my trucks as well. I've had a jar setting on my desk at work with equal parts of DOT3 and DOT5, that has been mixed together multiple times, been there in below freezing temps and there in 100 degree temps, no sludge, nothing wierd after nearly a year.....the only observable difference is they clearly don't mix and the DOT 5 aerates real bad and takes a long while to release the air, the DOT 3 seperates within minutes of shaking. Like mentioned already.....the TM says that DOT3 can be used if your in a pinch.

Its my opinion that the "sludge" that everyone seems to find is from the water that collects in the low laying areas of the system from the DOT 5 repelling the moisture instead of obsorbing it. The water is also the culprit for the rusty and leaking wheel cylinders that plague military vehicles.

DOT 3,4, and 5.1 are far more superior than DOT 5......the only advantage that I see with DOT5 that is benificial to the military is its greater shelf life due to its ability to not obsorbe water, but its disadvantages outweigh its limited advantage.

 

[AZDeuce]

Jake/Jeff/Recovery:

Thanks for the info where to look, and I concur, now that I know the airpack is involved, to buy a new one and rebuild the ENTIRE brake system at one time!

Thanks for all the advise, but more importantly telling me where to read up on this stuff. - Thanks!

 

[scrapman]

My own use has been to completely flush the system with DOT 3 with no ill results. I vacuum bleed at the airpak 1st then the wheel cylinders, be prepared to use 6 to 8 qts of fluid. That is why I buy store brand fluid as a disposable item in 1 gallon containers. As a lube I use ATF or Marvel Mystery Oil. A little bit goes a long way.

 

[AZDeuce]

Scrapman, thanks for the lube advice I was wondering what to use.

Now.......where do I put the lube? In the big can end, or the smaller valve end?

 

[Jake0147]

I use DOT 3 in my trucks as well.

This is the route that I chose. The reason being this: It's not a "sealed system" like today's vehicles. You either need to do significant (but doable) modifications, or you have to accept a vent that's open to the atmosphere, and thereby a moisture supply.
DOT 5 will NOT carry any moisture, therefore it will settle to the bottom. Flushing brakes through a quarter inch line, and hoping to get enough flow to expunge any moisture from the bottom of a very large wheel cylinder when the bleeder is at the top... IMHO that's a crap shoot at best. The army did testing for THEIR use of the trucks. My use (and most collector's use) is different. DOT 3 or DOT 4 will absorb some moisture, it has a tolerable "moisture holding capability" before it's considered contaminated, and even once it reaches "contaminated", it still absorbs more. Thus annual flushing can actually remove a much, much greater portion of the accumulated moisture. Everyone's mileage may vary with this, but for me it's a no-brainer.

Its my opinion that the "sludge" that everyone seems to find is from the water that collects in the low laying areas of the system from the DOT 5 repelling the moisture instead of obsorbing it. The water is also the culprit for the rusty and leaking wheel cylinders that plague military vehicles.

I agree 100 percent with the moisture being behind the leaky wheel cylinders. Not so much so about the sludge though. A sludge that is actually suspended rust particles (rust brown fluid being bled from the cylinders), but not sludged fluid.
I would highly recommend another glass jar be placed next to the first. Half with DOT 3/4, and half with power steering fluid, which is frequently sold in bottles that look IDENTICAL to brake fluid of the same brand. If you're really curious, the same test with DOT 5, and the same two tests with engine oil.

It is my OPINION that the resiliance of DOT 5 to contamination with the wrong fluid is a big part of it's popularity with the military. In a pinch, about anything non-compressable will allow the truck to complete it's mission. Remember, seal damage is not immediate, and the cost of a brake system overhaul is huge to you and me, but to the military it is often a lot less significant than an incompleted mission.
Again, that is opinion only, I haven't seen it written anywhere.

DOT 3,4, and 5.1 are far more superior than DOT 5......the only advantage that I see with DOT5 that is benificial to the military is its greater shelf life due to its ability to not obsorbe water, but its disadvantages outweigh its limited advantage.

Indeed. Great for them, not so much so for me. Shelf life and a universal fluid that fits virtually anything that they own easily makes up for the extra servicing that is required. DOT 5 fits that bill, and that of short track race cars, but I don't see any advantage to using it on a properly working brake system that is not overusing the physical size of it's brakes. Deuce brakes are old by modern standards, but the size (heat buildup and dissipation) of it's foundation brakes (the mechanical part at the wheel ends) is more than satisfactory and actually pretty good, even by modern standards. That part, the part that is most responsible for the temperature requirement of the fluid, is not deficient. (Please note, I'm NOT referring to the single outlet master, or to the booster that was designed and balanced long before universalized pedal effort standards were in effect).

 

[AZDeuce]

Well......you'll all should be proud of me, I learned to use the SEARCH page on this site. I typed in airpack, and got way too much stuff, and never did find the info I was looking for. But, then I typed in "lube airpack", and all I needed to know was right there. COOL! I especially appreciated the post by Dabtl (hope I spelled that right) with all the pretty pictures of the airpack. I am now informed, and no longer scared......GOD HELP US ALL!

And according to Jake0147 I will be flushing my brake lines (with ALL the wheel cylinders disconnected) and going to DOT 3, does that make sense?

 

[StreetbikeDepot]

If converting to DOT 3 an easy way to seal off the master cylinder vent from atmosphere and still allow for expansion is by using a vent bellow.

(VB01) Vent Bellow Breather

They are nice for trannies, transfers and axles also.

 

[AZDeuce]

Streetbike.......thanks for that info, and the link.

 

[REO 54]

So is your breather cap on the MC swapped out for a non-breather cap,then install the vent bellows breather?

 

[StreetbikeDepot]

There is a breather fitting on the MC cap, the bellow can be attached to that with a short piece of hose to get it out of the way.

 

[REO 54]

Ah,thank you for the info StreetBike.

 

[kastein]

I stand corrected on the sludge forming issue.

As for the seals - good to know that DOT 3 does not (apparently) harm seals in M35 brake systems. I'll probably use it simply because it means I can keep one type of brake fluid on hand for all my vehicles.

 

[AZDeuce]

Saturday evening I was able to remove the J pipe and put several good squirts of tool oil in the new (small cannister) style cannister. I started her up, and let her build up pressure then worked the brakes several time with NO sticking pedal so I drove it around on back roads, and it worked as the good Lord intended. I had to drive it to church the next day, and it gave me no problem's until I manuvering to park her and back her into a spot, I must have used the brakes three to four times in quick succesion (spelling?). The pedal got firmer, but the truck stopped fine.

On the way home she was fine, until I had to slow down to turn onto my street, and hit the brakes 3 to 4 times in a short period of time, and the pedal got harder, but the truck slowed down fine. As a matter of fact as soon as I got around the corner I slammed the brakes with it's hard pedal and locked up the brakes.

I know somewhere I have a slow brake fluid leak, as it will have a low master cylinder after a couple months. So I think the air pack is now fine, and the hard pedal only appears after rapid applications of the brakes, so it purges the air out of the hydraulic system and thus the harder pedal.

But it's a whole different kind of "harder" than when the air pack would lock up, then the pedal was hard as in SOLID, and you couldn't push it hard enoutgh to even slow down, much less stop. So I think my air pack is now fine.

I plan on jacking up the truck and repack ALL the bearings, install new grease seals, and those little cork seals. I plan on installing all new flexible brake hoses, master & wheel cylinders, and now I think I'll install a NOS air pack, that way EVERYTHING, except the steel lines will be new, and I'll flush/blow the lines out. I got everything now to do this except the air pack, but a friend here locally may have a NOS one for me. So pretty soon I'll have GOOD brakes, well as good as they can be, but for now, my deuce is safe and usable if it's needed.

THANKS for all the advise/help