Think my air pak needs a rebuild

[LiqTenEXp]

Hey,

I have been having issues with being locked out of the brakes completely on my M35A2. April 2009 I bled the brakes and inspected the whole system. It would easily lock up all 10 tires if you wanted and under normal braking it didn't pull to one side. It has a nice straight line under braking. I am not losing any fluid and have not had to add any additional fluid since April 2009.

This is the description of my symptoms:
You push on the brakes and it get stiff. Next time it doesnt's move at all. In this state there are NO brakes. With some pumping brakes come back to normal and may act fine till the next application of the brakes.

The pedal comes back to the floor instantly due to the spring but you can feel that behind the pedal the actual brake pressure hasn't been released back to fully off. It is sluggish returning brake off position.

I have done a bunch of searching around and talking to member online and this is what I have done so far:

1. Always drain the air tanks before/during/after trips
2. Added methanol based truck airline product to prevent freezing
3. lubed air pack using air tool oil via J pipe removal

Nothing has made any improvement. Would you all agree it is time to rebuild the air pack? I am sure you guys will say yes but just in case I am missing anything let me know. Could there be a problem with my Master Cylinder in reference to the slow return problem?

Thanks!

 

[dabtl]

I found the rebuild quite easy. I used an emery cloth to clean the hydraulic cylinder, but I believe a brake cylinder hone would work much more easily.

Just follow the TM. I have found the gasket for the air cylinder end cover to be a wee bit too small. I made one with a gasket cutter and soaked the others in BFS and they appear to slide on more easily. Do not bother experimenting with rubber gaskets, ask me how I know.

Nothing to it really. I think you can use the search function to find the thread on this.

 

[Jake0147]

You may be on the right track... Before you go much further, check the pushrod adjustment per the TM. not enough free play can and will do this, but it requires driving. The hard pedal is from no relief of the fluid, and the no brakes comes from overheated shoes. Hot brakes all around will be a side effect.

You can also check for a restricted vent from the airpack. If air gets in but can't leave, pressuring both sides of an actuator is the same as pressurizing neither side of the actuator.

There is another air issue that's happened on occasion, but I think it actually locks the brakes down hard as well. But just for grins you can go to the left rear (service) glad hand and check for pressure when the service brake is not applied.

If oiling the airpack required removing the J pipe, then it is a newer design, and I am of the understanding ( <--- that is NOT knowledge...) that it requires a different seal kit from the "standard" ones that have the pipe plug where oil would be applied. Somebody should probably confirm that before you make big decisions worth actual dollars, but I think there is a common kit out there that won't fit.

 

[dabtl]

Removing the J pipe is much easier than the plug. Until you disassemble the entire unit the plug is likely to be frozen in place.

 

[LiqTenEXp]

I tell you what. I will go out and take a picture of it and you guys might be able to help me find the right rebuild kit for it then. Probably tomorrow since it is dark out already.

Jake0147, the no brakes problem I am having has nothing to do with over heating. I am talking about <5 mph from a cold start sitting over night in my driveway. There's no heat being built up going <5 less than 20 feet.

 

[LiqTenEXp]

Pictures of the air pack.

Being that I am having issues with the pedal coming back properly, could there be an issue with the Master Cylinder and not the air pack?

 

[LiqTenEXp]

This my be my next step before doing the rebuild:

http://www.steelsoldiers.com/deuce/41984-deuce-brake-pedal-hard-but-no-brakes.html#post465756

 

[gimpyrobb]

Make sure you check post #8 in that thread. I have had that issue too!

 

[G-Force]

If you do wind up rebuilding it could you measure the bore of the brake cylinder and the stroke of the cylinder and PM me the info.
Also, if there is an NSN or part # on it that also would be greatly appreciated.
That looks like the old style air pack if I'm not mistaken.

 

[dabtl]

It is the M35a2 pack. Rebuild kits are relatively cheap for it.

 

[baxter]

It loks like it has the plug in pic #2 you can put oil in there if it will come out. As stated before you may have to pull it apart to get the plug loose I had to rebiuld mine but my brakes were locked on the air pack would not release at all.

 

[Irv]

I cleaned out my 5T airpack and it was dirt simple, no pun intended. Well, maybe a smidge of an intention.... No real reason for new gaskets. Nothing was deformed. Worked great afterwards. Just use common sense to put it back together. Irv

 

[dabtl]

Your tank uses a hollow hex nut rather than the normal square pipe plug. It will be much easier to remove.

 

[LiqTenEXp]

I am going to try the clean out MC trick today and see how that goes.

 

[gem1410]

How did you end up working on your brake airpack--A few of the trucks have the brakes locking up--where did you find the tm--Thanks George

 

[LiqTenEXp]

I got the air pack rebuilt today. Reinstalled it and started bleeding brakes. I need to replace a compression fitting for one of the air lines out of the airpack. It is leaking upon release of the pedal fairly severly. I am guessing it's the one that returns unspent air back to the air tanks. Pedal feels good but I need to take it out on the road after fixing the air line. I will let you know how it comes out.

 

[LiqTenEXp]

Brakes are great!!!

The feeling of being locked out of the brakes was definitely the airpack. The other problem i had was slow pedal return, that was the master cylinder. I replaced that also.

Rebuilding the airpack was totally worth it. Mine was in great shape without any scoring internally. It was a definite candidate for a rebuild.