Need some m35 Brake Help

[tklm539]

I really need some advice one the deuce brakes.

Everything has been working fine. This morning I went out to move the deuce and the brake pedal had about 4� of free play prior to beginning to engage the brakes. The truck still stops but the pedal is very spongy.

Here is what I know or think I know. There do not appear to be any leaks of fluid or air. The compressor is building pressure and I used my air tools to check. I question if the air is getting to the wheels.

I am not sure where to find the fluid reservoir for the brakes. I did not find it on the firewall where it would be in a car. The shoes may be out of adjustment, but I cannot see how that would have made a difference overnight.

The only thing I did different, is I got stuck on wet grass last night (desplined fronts) and used the winch to get out. Other than that it has been business as usual. Any help would be greatly appreciated.
Tom

 

[bugei]

the fluid reservoir is under the drivers seat.

mine did simular stuff, required a bit of a "pump up" before every stop. replaced the master cylinder, bled the brakes and now i can lock it up, ALL UP.

WARNING, the military used DOT5 fluid, look for signs of DOT5 or SILICONE before you fill the master cylinder with the wrong stuff. they are rumored to not mix well with DOT3.

there is a GREAT brake trouble shooting tree in the TM in the tm section.

http://www.steelsoldiers.com/index.php?module=pagesetter&type=file&func=get&tid=1&fid=file&pid=13

 

[SierraHotel]

Actually, it’s under a little door that is between the driver seat and accelerator…well, on mine anyway…

 

[rdixiemiller]

You probably have a dry master cylinder. Mine does the same thing every 3 months or so. One of these days I'll put the kit in the MC that has been in the basement for a year.......

 

[m-35tom]

it is just amazing how many people drive around with questionable or unsafe brakes and have never even checked or looked at any part of the system. what do you think is going to happen when your brakes fail unexpectedly and just when you really need them??

 

[serp]

i check my fluid once a month. i see no visible leak and i still check it. you only have a single reservoir master cylinder. no fluid no brakes. check it often.

 

[73m819]

get the tm-10

 

[jimk]

You will need to remove the vent line before removing the master cylinder cap.

I use compressed air, at 20psi, in the fitting on cap, then make the rounds (wrench for the bleeder, bottle and hose to catch the old stuff). The air pac has a bleeder screw.

If the pedal is hard but low (or brakes drag) you need to adjust the brake shoes. That is easily done, with the wheels on, from behind the backing plate. Top bolt is for the "minor" and top and bottom for the "major" adjustment). I'd suggest reviewing the prceedure in the book then start with the 'minor' adjustment using the feel of drag at wheel instead of feeler gauges. Brake adj. should be tight as possible but not drag. JimK

 

[tklm539]

I think the brake shoe adj. is the ticket. I followed the TM and pulled all the wheels. Some of the pads were a little off some a lot. Tried it out shortly after and all was back to normal. I used it for work this evening and and all is still well. Thanks

M-35tom, was that a rhetorical question? I know where the parts are and have gone over the brakes several times when servicing the truck. I live in the mountains, when the brakes fail unexpectedly, I fail to see how knowing where every part on the brake system is will help when careening down a hill. The point of the post was to solicit assistance prior to a real problem. By the way, thanks for the useful information.

Tom

 

[CCATLETT1984]

Re: RE: Need some m35 Brake Help

WARNING, the military used DOT5 fluid, look for signs of DOT5 or SILICONE before you fill the master cylinder with the wrong stuff. they are rumored to not mix well with DOT3.

When mixed dot5 and dot3 make a thck goo at the bottom of the MC, it will clog the lines and destroy the seals on the wheel cylinders if it makes it that far, silicone is purple (at least the new stuff is) if you put some of the fluid in question in a jar with a few drops of water and shake it up a lot, dot5 will not mix with the water. dot3 will.

 

[houdel]

it is just amazing how many people drive around with questionable or unsafe brakes and have never even checked or looked at any part of the system.

A good point. Brakes are probably the most critical component of a vehicle, and generally the least understood by the average shade tree mechanic. Engines, wheels and tires, cooling systems and drivetrain parts are right out there in the open and easy to work with and understand. Other than the filler opening in the master cylinder, the rest of the bake system is pretty much a mystery for most people. To their credit, the members on this site seem to much more aware of and more attentive to brake issues. Of course when piloting a 13,000 pound or heavier vehicle on the street you'd better be damn well confident you can stop it when you need to!

 

[jimk]

ANY vehicle braking system can, and should, be tested. Get er' going, check the mirror, mash on the pedal hard as you can...And if you break something, well, better now than later. JimK

p.s. If you can't mark the pavement try dirt

 

[m-35tom]

good advice jim, every owner should inspect the brake lines for rust and damage at least yearly. since most m-35 are still single circuit brakes, any failure will be a problem. you don't have to be moving, just use both feet and push on the pedal like you want to break something. nothing should happen, but if a line does burst it will be because it was getting weak for a reason, either rust or a hose worn or aged. i replace all the lines and hoses on all my trucks as well as upgrading them to dual circuit for safety. it is a small investment in $$.

 

[bugei]

tom, hopefully, this is not a hijack, not ment to be.

is the mod to dual circuit a mater of changing the master cylinder? what master cylinder are you using to convert to dual circuit?

thanx

 

[houdel]

The stock M35 split brake system used a dual cylinder master cylinder and two AHUs. It split the brake system left/right. Were I to convert mine I would use a diagonal split system so you don't get "brake steer" if one side failed. I'd like to know what tom used for a M/C also!

 

[bugei]

ahu? air pack? ooohhhh that sounds expensive

 

[m-35tom]

dual brakes

i always split front and rear, anything else sounds scary...........
i convert to full air over hyd and use the foot treadle valve from something with full air brakes. the pics show the last truck i did (am doing) with the brake pedal and valve from a 900 series mounted on the firewall. i used the brake system from a UD (nissan) truck and also the air drier from that truck as it is a pressure operated auto drain system. (there are two air actuators and master cyls side by side, buy you can only see the outside one and the rear bracket of the inner one.) you can add another airpac and mount a dual master cyl and achieve a similar setup.

 

[m-35tom]

RE: dual brakes

also total cost of conversion was under $200. new 900 series assy and used mc unit that i then rebuilt.

 

[jimk]

RE: dual brakes

...you don't have to be moving...

For a pressure test, however marking the road can help verify there are no frozen wheel cylinders, capped lines, oiled shoes....JimK

p.s. Stalwart is dual, using ISO-15 mineral oil(over air), stations LF,RC,LR for the left airpac and RF,LC,RR for the right. Surely done this way for the same reason Lee points out.

 

[bottleworks]

The stock M35 split brake system used a dual cylinder master cylinder and two AHUs. It split the brake system left/right.

IIRC, the dual system had one piston/circuit for the front axle and the second piston/circuit for both rear axles.

What's everyone's typical brake pedal height?