M135 Advice please.......................??

[Brad]

Oh, in case anyone is wondering.
Dad was in the 7th Division 32 Regimental Combat Team (7-32 RCT)
Battery B, 48th Field Artillary
The 91029 is his birthday

 

[OkieM1008morrison]

Wow that is a great looking 135!

 

[Brad]

Hello all,
Saturday morning here my Son and I took the truck to a big local parade. About 30 mile round trip, not counting the parade.
Had nothing but trouble with these brakes just keep locking up. I think it is mostly, if not all the front passenger wheel cause when it grabe it pulls hard right.
If you ever drove in a parade you know its all stop and go.
Man what a pain, evytime we'd touch the brakes it would grab. Then to pull out its really hard on everything until it reeleases.
And it seems like it is dragging all the time also.
Just Thursday when I drove it it was really free wheeling. Lots of power. Now it seems like it's just dragging, or worse.
I have been dealing with this ruck for years now and it's always these brakes.
As nice as it is, and as well as everything else does, and it runs fine, it just is a real problem.
It really isnt safe cause sometimes grabs hard. I am just tired of it. I do not know what to do. I have tried everything I can think of or has been suggested that I am physically able to do.
But thanks all for your help.

 

[Another Ahab]

Hello all,
Saturday morning here my Son and I took the truck to a big local parade.

And it seems like it is dragging all the time also.

I do not know what to do. I have tried everything I can think of or has been suggested that I am physically able to do.
But thanks all for your help.

 

[armytruck63]

Sometimes when a vehicle pulls to one side, it's because one or more brake shoes on the other side of the vehicle is soaked in oil or brake fluid. I've had this happen with an M38A1 and an M35A2. It's even more noticable if it is one of the front sets of brake shoes that are wet.

Maybe a local brake shop can sort things out for you. Other than the air-pack and electric parking brake (if it is still present), the rest of the system is a traditional single circuit hydralic brake system, albeit with two wheel cylinders per wheel. These trucks have truly impressive brake systems when everything is dialed in.

What type of brake fluid are you running, DOT-3 or DOT-5? Whichever you are using, don't mix the two together or things will get really screwed up.

Good luck with this. The truck is worth the effort.

 

[frank8003]

Just for testing or in an emergency to get home.
I am ready to get slammed for this BUT............

A few bucks for fittings and a half hour.
Disconnect the line to one wheel, like the right front at the "Tee"
and plug it with an inverted flare plug.
Drive and see if it all works better -no dragging. If it is front then plug off them both for a test.
3/16", 1/4" or 5/16" inverted flare plugs needed, or whatever fitting is necessary, I don't know from here.
Drive it around a bit to find if the problem goes away" then fix that one brake mechanism.
Spend the time with your Dad that you saved guessing about the brakes.

 

[hendersond]

That is exactly what I was afraid to say. I hate getting beat to death for a posting. I'd plug the thing right where she splits to the front end at the tee by the air pack and try it. I would never leave the yard of course. You may be surprised what happens. I'm betting on a hose problem.

 

[hendersond]

Blowing thru a hose with 120psi is one thing. I don't think those return springs put 120 psi back into the system. You could also have a combination of problems like reduced pressure to the rears like I did. The others locked up quick. I suppose the right way is with some sort if pressure gauge. I wonder what the developed line pressure is?

 

[Brad]

Thanks again guys.
I had pretty much thought of doing just what yer suggesting. Plug one or both front wheels and see how it works. Then I'd at least have the trouble isolated.
Maybe just let it all at that. Id still have four wheels breaking the truck and we never really have a load on it.
But I dont know what I'll yet do this year. Winter is a coming on and I have lots of regular chores ahead of me.
Thanks all

 

[Another Ahab]

Thanks again guys.
I had pretty much thought of doing just what yer suggesting. Plug one or both front wheels and see how it works. Then I'd at least have the trouble isolated.
Maybe just let it all at that. Id still have four wheels breaking the truck and we never really have a load on it.
But I dont know what I'll yet do this year. Winter is a coming on and I have lots of regular chores ahead of me.
Thanks all

Well, hope you'll keep us posted, whatever you do:

- That M135 is clean; a real beauty.

And please tell your Dad hello from all of us. I don't believe I'm alone in wanting him to know that he has a fan base here!

 

[hendersond]

I have been re-reading your posts on the brake problem. I'm unclear on a couple things.
How do you bleed them? by foot or power bleeder?
The reason I ask is a power bleeder using very low pressure tells you a lot. For example if the fluid flows out of all 12 wheel cylinders (with absolutely no air to the airpack) with the exact same flow and pressure you have no blockages in 1 direction. I'm suspicious there is reduced flow to another axle or wheel causing increased pressure or flow to your one wheel. Remember it is pressure, volume of stroke and square inches of your wheel cylinders. One restricted rear hose impacts 4 wheel cylinders.
My memory says there is only 1 high pressure line out of the airpac that goes to the frame and it splits 2 ways front and rear. The rear line splits 2 ways for the 2 rear axles. Trace your lines and tell me if this is correct on your truck. If it is, you will be able to release your 1 front wheel at any rear wheel cylinder. If you cannot, you need to look at hoses. I will PM you my phone number.
Dan

 

[hendersond]

I remeber that possibility from last year.
I sort of rulled that out when I cracked the fitting ahead of the rubber lines and the brakes released instantly.

Crack a rear one. the front should release. Lock it up again and crack the other 7 rear one at a time. Then crack the drivers front. They all should release the passenger front wheel.
If you find problems with 4 cylinders on an axle, pry the hoses out of the channels on top of dog bones. Stand on the brake with the truck running to re-expand the hoses.

 

[hendersond]

I keep trying to sleep and ideas keep coming! If your right front wheel is locking up, it is getting flow and pressure to it. If the other is not locking up equally, it has reduced flow (restriction in line) or the pressure is not getting to the shoe to the drum (hung up shoe on backing plate).
Same holds true for the other 2 axles. We are focused on the one locking up. Lets look at the system as a whole.

You may have 2 different problems. Free flowing return from 1 wheel and a reduction in shoe pressure contacting the drum somewhere else.

I would
1. Put all 3 axles up in the air at the same time, lightly apply the brakes and ensure all stop equally. (remember both rear axles are gear driven together thru the t-case. 1 brake working will stop the other 3 rear wheels. I had to unbolt a driveshaft to figure it out) This will tell you who gets and who does not get pressure and volume. If any do not stop crack the line at the wheel. High pressure there but no contact between drum and shoe indicates a hangup inside. Separate the hydraulic from the mechanical in your mind.
2. Bleed all 12 cylinders and make sure all flow equally. if one dribbles and the other squirts, you have restricted flow to the cylinders. Look at hoses. I use about 12 psi in a power bleeder. Pushing the peddle gets you high pressure. I'm guessing hundreds if not thousands of psi with a working airpac.
3. Every wheel cylinder should be able to release your RF locked wheel, If not you have a restriction in return flow. This is usually a collapsed hose inside where you cannot see it. Remember this is low pressure from the return springs on the shoes.

 

[Brad]

Hi Dave, thanks again.
We bleed the brakes the only way I know how?? My son works the pedal and I crack the bleededs at each wheel, starting with the farthest first.
I believe the lines tun the way you describe, but I will check once it warms up a little.
I also bleed the air pac.
Also, I think you are correct about being able to relieve the line pressure by cracking any bleeded.
I need to make clear the main reason I was reluctant to think it was a rubber line at either front wheel when locked up.
If I cracked the line where it enters the rubber line, BEFORE the wheel cylinder it will release pressure.
This makes me think the blockage, if any, is between the airpac and any of the rubber lines.
Now just a thought. Perhaps one of the rubber lines from frame to axle??
Thats why I am going to replace them ALL.
But agai, could there be any truth to the longer cylinder rods where I replaced them with Canadian ones???
Thanks, man I apreciate your help.
Happy New Year

 

[hendersond]

Hard to follow without actually seeing it. So you are cracking the steel line on the axle and it releases the wheel?
Dan

 

[hendersond]

Also, are you bleeding the airpac first? I remember 2 bleededs on it, but cannot remember the order.
Next question, are you bleeding without air pressure assisting?

 

[Another Ahab]

I have been re-reading your posts on the brake problem. I'm unclear on a couple things.
How do you bleed them? by foot or power bleeder?
Dan

Crack a rear one. the front should release. Lock it up again and crack the other 7 rear one at a time. Then crack the drivers front. They all should release the passenger front wheel.

I keep trying to sleep and ideas keep coming!

This series of (3) posts is like an all-in-one primer on troubleshooting drum brakes:

- It's Excellent

- Too bad there's not some way of squirreling it away as a "best of" for future searches

Good stuff hendersond. Outstanding.

 

[hendersond]

Thanks. Maybe when this is solved I could combine everything we learn and write a summary. We will see.
Either way the end result for both of us will be "Huh, I never thought that would have been it in a million years."

Looking at the technical manuals it looks like the brake lines get up to 1,200psi after boost by the airpac to push the wheel cylinders pistons out. My fish scale shows 28pounds on the return spring. Multiply that out by the square inches of a Canadian wheel cylinder piston and you get around 20 psi produced to push fluid back into the airpac.
The TM also states 3 more interesting things.
1. There is a right and left backing plate and adjuster parts. Could they be switched?
2. The airpac senses the return pressure and pulls fluid back to help the return springs. The vent line must be clear to the intake manifold.
3. One side of the wheel cylinder has a longer stroke. The side opposite the adjuster.

I have to think about how this impacts the problem.
I remember a discussion about the longer rods related to #3 where the piston could possibly be pushed back far enough to cover the port. I would not thinK bleeding would help release the shoes then????

Dan

 

[m1010plowboy]

G 749 Brakes

I found some of Gunfreaks research on the wheel cylinders and the difference in the bore. http://www.steelsoldiers.com/showthread.php?73907-My-GMC-a-little-update/page19

Page 19, 20 and so on covers the discussion.

Canadian 1 3/8
Early American 1 1/4

I saw it somewhere, some thread here or there, info on the difference in the Rod 7412067 but I didn't find the sizes yet so we should post them once uncovered. The pic shows a scale which doesn't really work so getting the two cylinders in hand, measuring and snapping a picture would help.



I get to trouble shoot an M211 that was re-built a few years ago. I'm now thinking that we should do what you did and get 6 wheels in the air, remove drums and make sure the 'return' springs are pulling the pads back on their own before we air up and bleed the system.

Not sure if anyone's been "shopping" lately but I see a few items out there at better prices, if you hunt. I'm looking for 24 wheel cylinders by March so when the prices are in the $12-$15 range it's worth replacing them with new ones. If a guy searches "G749 parts" "M211 parts" and "M135 parts" you get a few different results.

 

[m1010plowboy]

Wheel Cylinders

Did we get this done yet?

I grabbed some photos of the WAGNER F-15306 wheel cylinders and measurements.



When I pulled it apart the 'storage oil' or whatever they use to lubricate it had hardened and glued them together.



Just something else to check before a guy takes one out of the box to install it, make sure they work properly.

I played with the return springs on a spare brake assembly and they return the brake pad easily. The bolt that holds the lining to the backing plate could cause resistance if not installed correctly. Get er done.