No brakes!!!

[DDC2StrokePower]

i have an M211 and i was driving down the road the other day and went to hit the brakes and there was nothing there, had to pump em a dozen times to get it to slow down. when i got back to the farm i opened the hood to check something and found brake fluid had sprayed all over the engine. it came out of a line that im assuming ran to the old oil bath air cleaner, mine has been retrofitted with a regular automotive air cleaner. im not sure really what happened, the brakes work ok now, little bit leary about drivin it down the road, i traced the line going back and it goes to a diaphram looking valve on top of the air pack. i also noticed that there is air leaking out of this line whenever there is air in the tanks. does anybody have an idea on what happened and how to fix it.

thanks

 

[topo]

Just maybe the air from the air pack flowed back to the master cylinder and up the vent to the central vent right by the old air filter . this one vent is tied to every thing check your master cylinder to see if air is bleeding in to it ? years back I over filled the gas tank on my GMC and on steep roads got gas in my brake system .

 

[m1010plowboy]

Brake troubleshoot

Without actually seeing it, and picturing lines disconnected, it's time to shut er' down.
I drove my 12,000 lb truck all day and can't imagine brake failure........without a stuck throttle at the same time.

You'll need to get underneath ....take pics..., trace all the lines and become absolutely familiar with the current set-up and how it works. Sounds too modified for a guess.

MilitaryTrucks.ca - Welcome! maintains the Tech Manuals that you'll use to compare your current set-up with how things are supposed to work. Go to the bottom of the M135 page (Part 3 of 4) TM 9-8024 pg 435


With air leaking and fluid dripping this girl is screaming for a whole bunch of personal downtime with you.......glad you listened to her.......

Here's the air-hydralic cylinder, Now show me some pictures and let us know what got modified.

 

[DDC2StrokePower]

in the one picture of the engine compartment i circled the vent line that all the fluid came out of, and this morning i removed the top line from air pack, and when i ran the truck there was steady air pressure coming out of it, one other thing, when i filled the fluid reservoir it was a little over full, not sure if that would make a major difference or not

 

[m1010plowboy]

Thems the brakes

My M135 is silent once the key is off.......so far. Air is not supposed to "leak out".

The compressor fills the air tanks, which applies additional force in the "air/ hydraulic cylinder" once the brakes are applied.

My M135 brakes stop the truck with very little pedal pressure, if you need to push hard on the pedal the air assist is not working.

On the back of the compressor is the "output" air line from the compressor to the tanks. If you can undo that fitting and hook up an independent compressor you can "charge" your system without the noise of the motor. For the brakes to properly stop the big truck in a "throttle stuck, emergency stop" situation this "air system" must work properly.

Trouble shoot that part first to see if she'll hold air.

Things to check:

- Air tank drain screws closed
- All air leaks fixed
- Air gauges working, reading 90-100 psi min.
- Faraday low air warning system....under dash.....makes buzzer noise below required PSI, check connections.

From the pictures it's real tough to per-scribe medication for the patient because it looks so different from original. Let's figure it out.

 

[m1010plowboy]

211 Brake system

The top 3 lines on the air cylinder are air lines.

If you have fluid coming out of the top line..... item "C" on page 46, then it's by-passing inside the air cylinder. Fluid in an airline, returning to the MC could cause overfill appearance. Air in fluid, fluid in air.........good catch before it's terminal.

My "Fluid Reservoir" . . . . .master cylinder MC, under my dirt boots on the drivers side floor, is "Full" to the top and can't be over full.

What kind of fluid set up do you have?

 

[DDC2StrokePower]

well all valves are closed and it is not leaking air anywhere else, i disconnected the line off of the top of the air pack and that is the air leak. went to drive the truck and as soon as i pushed down the brake it was like a rock and the brakes were locked up. i put a fitting and a piece of rubber hose on it, and put a kink in it then the brakes would release, but when i drive it down the road i have to pump the brakes a half dozen times and then they begin to work. i also found that there is fluid running out of the bottom of the air pack. i have dot 3 fluid in it now

 

[DDC2StrokePower]

for some reason my computer wont download the manual

 

[Superdave]

Time to pull the air pack as by the sounds of it the valve is shot where you have the air leak (the valve that is just in front of your second picture held on by 6 screws) and the valve in behind it could be could be leaking the brake fluid which is sending it through the air release line up to the air cleaner.

 

[Gunfreak25]

Yep, if that truck sat for any more than 5 years the air pack likely needs a rebuild. Some get lucky, most don't. My AIR PAK seals and O rings were all disintegrated and melted from sitting in old brake fluid for so long.

The good news is you can get a new one from Alfa Heaven for $200 or rebuilt it yourself for half the price. The M813 series 5 ton AIR PAK rebuilt kits will be 99% compatible and can be had for $50 if you search around. The only thing you must do is take 1 part from a 5 ton air pack and swap it into the GMC air pack so the kit is 100% compatible. The "part" in question is called a "threaded fitting" in the book and is the part you remove with a large "homemade screwdriver". It is basically a threaded sleeve with a piston in it's bore. You take the entire threaded sleeve/piston from the 5 ton air pack and put it on the GMC air pack. Then 100% of the 5 ton kit works for the rebuild.

 

[DDC2StrokePower]

thanks for all the info, im new to this whole thing, ive only had the truck for 3 days now, but how hard is it to find the part out of a 5 ton?

 

[Gunfreak25]

I am willing to bet Memphis Equipment may have it in stock. I need to check myself as I am going to need to get mine back together sooner than later.

 

[DDC2StrokePower]

So I called up Memphis today and found out that the guy who used to know everything about that air pack retired in December. Not quite sure what to do now

 

[Gunfreak25]

Your best bet is to find an air pack core to use as parts. Option 2 is finding a seal company or brake parts house that carries the two little piston seals off the GMC air pack that the 5 ton kit does not contain. Let me call around tomorrow! The piston seals or "cups" look just like the old timey wheel cylinder cups that are donut shaped. And they are exactly 1" too. I was able to save 1 of my old ones so I may send it to someone for a possible replacement parts #.

 

[Gunfreak25]

In the meantime i've emailed a custom rubber injection moulding company for a setup quote on the GMC air pack piston seals. I would imagine it would be around $500. So anything is possible, it's just a matter of $$ most of the time.

When I get a quote I will post it in a new thread and see how many people here would be willing to pitch in for a group buy on setup costs.

 

[JGBallew]

Just a note, be careful who you field the airpack out to. Had one come in that was obviously a rattlecan refurb.
All shiny black outside, didn't work, full of rust inside.

 

[DDC2StrokePower]

Jb Ok thanks ill keep an eye out, and gunfreak if you find someone I'd definately be in

 

[Gunfreak25]

I was quoted $5000. Will be finding another rubber company. One with less overhead.

 

[DDC2StrokePower]

Wow that is impressive. So is it just the o-ring that is hard to get?

 

[Gunfreak25]

There are two of them on the small piston and they are more "cups" than O rings. The 5 ton kit does contain these two cups but they are for the 5 ton piston which is a different size. Fortunately, the 5 ton piston assembly swaps into the GMC pack quite easily.

I've got another place to call tomorrow. I think they will have the GMC piston seals in stock as their parts guy is about the most knowledgeable person in the whole USA when it comes to brake boosters and rebuilding. He said if it has a part # they can probably source parts for it.