Brakes Grab - M35A2

[plym49]

The brakes on my M35A2 are grabbing.

If slowing the truck using the brakes only from, say, around 10 or 15 mph, when I step on the brake pedal the pedal goes down a bit and then has high resistance, with no application. Press harder, and all of a sudden the brakes grab and the truck literally stops on a dime.

It is like I cannot modulate the brake pedal when coming to a stop.

Then, the pedal does not want to return up. When starting in gear, when the brakes are cold they are not released - I can get them to release by reapplying the brakes and lifting the pedal with my foot. Once the truck starts rolling they also release.

I have not tested this stopping from a higher speed due to not having a safe place to try this (and not wanting to risk flat spotting 6 tires).

The master is topped off with DOT 5. One thing I know for sure is that the brake return spring is totally rusted and must be replaced. I would have replaced it already but I am in the boonies at the moment; no auto parts stores around.

I figure that all of the problems are being caused by a totally slim shadied brake return spring, and I plan to replace it at my earliest opportunity (200 miles from now).

The reason for this post is to get some additional opinions on what this might be in case I need to dive deeper into this brake system.

Thanks in advance.

 

[LV2XLR8]

The brakes on my M35A2 are grabbing.

If slowing the truck using the brakes only from, say, around 10 or 15 mph, when I step on the brake pedal the pedal goes down a bit and then has high resistance, with no application. Press harder, and all of a sudden the brakes grab and the truck literally stops on a dime.

It is like I cannot modulate the brake pedal when coming to a stop.

Then, the pedal does not want to return up. When starting in gear, when the brakes are cold they are not released - I can get them to release by reapplying the brakes and lifting the pedal with my foot. Once the truck starts rolling they also release.

I have not tested this stopping from a higher speed due to not having a safe place to try this (and not wanting to risk flat spotting 6 tires).

The master is topped off with DOT 5. One thing I know for sure is that the brake return spring is totally rusted and must be replaced. I would have replaced it already but I am in the boonies at the moment; no auto parts stores around.

I figure that all of the problems are being caused by a totally slim shadied brake return spring, and I plan to replace it at my earliest opportunity (200 miles from now).

The reason for this post is to get some additional opinions on what this might be in case I need to dive deeper into this brake system.

Thanks in advance.

Fairly new to this but have already experienced some brake issues and it sounds to me like an airpac issue where the actuator ram in the pac is sticking maybe. Look up the topic, it's usually recommended to remove a fitting or airline from each end and to put a few drops of air tool lube in.
Good luck

 

[Katahdin]

Yep, see this thread:

http://www.steelsoldiers.com/deuce/61605-how-world-do-i-service-my-air-pack.html

 

[plym49]

Yep, see this thread:

http://www.steelsoldiers.com/deuce/61605-how-world-do-i-service-my-air-pack.html

Thanks, that was very helpful and I am sure that that is all or part of my problem. The brake return spring needs to be replaced regardless.

I am on the road with limited time and tools. How effective would it be - short term - to simply remove the air line at the compressor (easy to access) and shoot a good amount of light oil - like WD40 - into it? I realize that most will end up in the tanks, but perhaps enough will aerosol up into the air line that feeds the air pack to give me a better situation for the ride home. Will this work?

 

[Katahdin]

My personal feeling is to avoid WD-40 for this since it doesn't have the greatest lubricant properties. Air tool oil should be available at any Walmart, Lowes, Home Depot, Tractor Supply etc. Others have used Marvel Mystery Oil.

If you absolutely need to "spray it in" I would suggest "Rem Oil" (Remington Gun Oil) or Break Free CLP, also available at Walmarts and/or Dick Sporting Goods or most gun stores.

 

[rlwm211]

If the brake pedal is sticking, it is weither the airpack compensator and you can spray a gallon of oil in the airpack whether it be in the incoming air line, the back of the piston or anywhere else you can find a spot and it will not make a difference.

The other option is that the master is rusty in the main bore and it needs t be rebuilt or replaced because the piston is sticking.

Either way, this needs to be addressed otherwise the truck is not safe to drive.


Just my two cents....RL

 

[plym49]

My personal feeling is to avoid WD-40 for this since it doesn't have the greatest lubricant properties. Air tool oil should be available at any Walmart, Lowes, Home Depot, Tractor Supply etc. Others have used Marvel Mystery Oil.

If you absolutely need to "spray it in" I would suggest "Rem Oil" (Remington Gun Oil) or Break Free CLP, also available at Walmarts and/or Dick Sporting Goods or most gun stores.

I don't have enough of a window tomorrow to drive the Deuce (out of my way) to the nearest town with either an auto parts store or the chains you mentioned. It is field expedient time.

Here is what I have to work with: MMO, 3-in-One, and WD40.

If I can I will open the J tube and get it in there. If that is not feasible with the tools and time available to me (about an hour, two at most) then the only thing I can do is to open the compressor line.

So, given the above, which oil would you recommend? At the J tube? At the compressor line?

Edit: As a reminder, the above field expedient repair is only to allow me to drive 200+ miles tomorrow with an improvement over just leaving it as-is. Once I am at the other end, I can do a proper repair as needed.

 

[rlwm211]

critical point...If the brake pedal is not coming up, it is not the air pack

RL

 

[plym49]

critical point...If the brake pedal is not coming up, it is not the air pack

RL

Yes, the return spring is on its last legs. It is easy enough to raise the pedal with my toe after each application for the ride back.

One other potentially correlating factor. The brakes grab as described much worse when cold, and even more if cold and damp.

 

[plym49]

If the brake pedal is sticking, it is weither the airpack compensator and you can spray a gallon of oil in the airpack whether it be in the incoming air line, the back of the piston or anywhere else you can find a spot and it will not make a difference.

The other option is that the master is rusty in the main bore and it needs t be rebuilt or replaced because the piston is sticking.

Either way, this needs to be addressed otherwise the truck is not safe to drive.


Just my two cents....RL

Clarification: the brake pedal is not sticking. The brakes are grabbing. IOW a small amount of pedal pressure results in as forceful a stop as if you slammed on the brakes. The effect is more pronounced on the first stop or two when the brakes are stone cold. The brake pedal is not returning upwards as well as it should because of a bad return spring - but it is not sticking.

 

[rlwm211]

I would try bleeding some fluid out of the airpack and see how rusty it is and how much gunk is in the fluid.

The compensator is the hydraulic portion of the airpack that regulates the braking action. The air valve is sprung against the compensator and can stick. Typically, the compensator is where the problem usually lies as it is a place where moisture seems to aggragate and cause corrosion and any impurities can also get stuck there.

I recommend lubimg the air pack by squirting some air tool oil into the air line preceeding the air pack. If you remove the two bolts holding the shield on you can then swing the air pack away from the frame far enough to get to the air line and loosen the nut and take the line off and apply some lubrication.

I have always hesitated from adding lube in the line from the compressor because of the air wipers and not wanting to get oil on my windows from their exhaust.\\RL

 

[plym49]

I would try bleeding some fluid out of the airpack and see how rusty it is and how much gunk is in the fluid.

The compensator is the hydraulic portion of the airpack that regulates the braking action. The air valve is sprung against the compensator and can stick. Typically, the compensator is where the problem usually lies as it is a place where moisture seems to aggragate and cause corrosion and any impurities can also get stuck there.

I recommend lubimg the air pack by squirting some air tool oil into the air line preceeding the air pack. If you remove the two bolts holding the shield on you can then swing the air pack away from the frame far enough to get to the air line and loosen the nut and take the line off and apply some lubrication.

I have always hesitated from adding lube in the line from the compressor because of the air wipers and not wanting to get oil on my windows from their exhaust.\\RL

From where do I bleed the fluid out of the air pack? From the plug where you squirt in oil (on the back side, I believe)?

I have Marvel Mystery Oil, WD-40 and 3-in One to work with. Was thinking of adding some MMO and then WD to help move it along (if I add from the compressor line). I'll try to add it at the J tube, but by fall back is to open the compressor line.

 

[rlwm211]

There is a brake bleeder at the top of the air pack that looks just like one from a wheel cylinder or a disk caliper. You will see a brake line descending from the master cylinder to the air pack and the bleeder is right near it. If you do not know how to bleed brakes, take the time to read the proceedure in the TM to make sure you do not introduce air into the system.

Where abouts are you in NY? I am near 13815

RL

 

[LV2XLR8]

From where do I bleed the fluid out of the air pack? From the plug where you squirt in oil (on the back side, I believe)?

I have Marvel Mystery Oil, WD-40 and 3-in One to work with. Was thinking of adding some MMO and then WD to help move it along (if I add from the compressor line). I'll try to add it at the J tube, but by fall back is to open the compressor line.

NO WD! It's more of a solvent than a lubricant. I've seen many guys at my work mistakenly squirt some in a noisy bearing and you should see how quickly it cuts through the remaining grease and cooks the bearing. I don't even own any anymore. Right stuff for the right job but I'd say use a real oil, the thinner and lighter the better.
Good luck and be very careful. As I've been told, the first time the brakes fail on a deuce is the first time you load your drawers.
Another word of wisdom from another SS member, always drive a deuce as if you had to stop with only your transmission and parking brake.

 

[plym49]

NO WD! It's more of a solvent than a lubricant. I've seen many guys at my work mistakenly squirt some in a noisy bearing and you should see how quickly it cuts through the remaining grease and cooks the bearing. I don't even own any anymore. Right stuff for the right job but I'd say use a real oil, the thinner and lighter the better.
Good luck and be very careful. As I've been told, the first time the brakes fail on a deuce is the first time you load your drawers.
Another word of wisdom from another SS member, always drive a deuce as if you had to stop with only your transmission and parking brake.

Yes, I was wondering if the WD would serve as a vehicle to get the lighter oil (MMO or 3 in One) moving along, not as a lubricant.

I actually always do drive my Deuce exactly as you describe. That's a lot of the reason I have only seen this brake problem at very low speeds - I usually drive such that I do not use the service brake until the vehicle speed is down to 10 mph or so. That is ebrake territory. However, an emergent situation could always arise. Also, even at 10 mph it is not fun having the brakes grab suddenly if for no other reason that it makes the driver look like a total noob.

Here is what I have decided. I know for sure that the brake return spring is NG. I am not going to drive the vehicle or shoot this bug any more until that spring is replaced. See, with a bad spring, you cannot really modulate the application of the brake pedal, and the brakes on my Deuce were always really good. Maybe they are grabbing because I cannot effectively modulate the application of the brakes.

I will leave the air system and components alone until after I replace the spring. That way I am only changing one thing at a time. If, after replacing the spring, I still have the same problem, then I will proceed according to the advice provided, adding the right oil at the right location.

That's my story and I am sticking with it.

 

[LV2XLR8]

Yes, I was wondering if the WD would serve as a vehicle to get the lighter oil (MMO or 3 in One) moving along, not as a lubricant.

I actually always do drive my Deuce exactly as you describe. That's a lot of the reason I have only seen this brake problem at very low speeds - I usually drive such that I do not use the service brake until the vehicle speed is down to 10 mph or so. That is ebrake territory. However, an emergent situation could always arise. Also, even at 10 mph it is not fun having the brakes grab suddenly if for no other reason that it makes the driver look like a total noob.

Here is what I have decided. I know for sure that the brake return spring is NG. I am not going to drive the vehicle or shoot this bug any more until that spring is replaced. See, with a bad spring, you cannot really modulate the application of the brake pedal, and the brakes on my Deuce were always really good. Maybe they are grabbing because I cannot effectively modulate the application of the brakes.

I will leave the air system and components alone until after I replace the spring. That way I am only changing one thing at a time. If, after replacing the spring, I still have the same problem, then I will proceed according to the advice provided, adding the right oil at the right location.

That's my story and I am sticking with it.

 

[plym49]

OK, I took some photos of my air pack and master for reference.

BTW, a related thread is here: http://www.steelsoldiers.com/deuce/61605-how-world-do-i-service-my-air-pack-4.html#post951473

Pictures of air pack:







Pictures of master:







I operated the brake pedal by hand from below. There is the correct amount of free play in the pedal. You can hear the air entering and exhausting from the air pack as the brakes are applied. IOW the sounds the system makes at the master and air pack are exactly what you would expect to hear. I did also hear some clunking at the right rear of the truck; I wonder if I have a bad return spring back there.