Help... Brakes Stuck on!

[sponaugle]

I took my M35A2 on it's first longer distance trip, and have run into a snag. About 2 hours south of Portland, and fortunatly about 5 miles from my desination, I had a brake problem.
I stopped at a Safeway, and after coming back out and firing up the truck, it would not move. The brake pedal was rock hard and would hardly move at all. It appeared the rear brakes were completly locked up. I vented the air packs and the truck would move freely.
I fired it up again, but after just a couple of stops the rear brakes were dragging very hard. I was able to get to the desintation (which happend to be out in the middle of no where) because if I didn't touch the brakes, it took a bit longer to get locked up.
Am I right in assuming this means the air pack is somehow leaking pressure across a seal? I'll have to leave the truck where it is and come pack with parts and tools to repair it.
So, the question is:

1) Is this a common problem, and if so is replacing the air pack the way out? Do I need to replace the master as well?

2) I will replace all the pads and all of the wheel cyliners as well, as the rears got VERY hot. Better safe then sorry.

3) Are there any temporary fixes (something I could lube) to get me home?

I understand I will need to know which air pack I have (there are two version?), so I'll snap a few pictures before I leave tomorrow.
Anything else I need to know to order parts before I leave the truck?

Disclosure of recent changes:

I bled the brakes (pressure bleeder) before leaving, which seemed to work great. I also added a second fluid resovoir feeding in to the MC thru the cap so I can see the level in the cab. No brake fluid consumption at all.

And, most telling (and of course my own fault), it seemed to be dragging the brakes a bit a few weeks ago, but then it got better.

thanks!!!!
Jeff

 

[jsthnt@gmail.com]

I had that same problem shortly after I got my deuce. I dumped all the air out of the deuce and it seemed to go away. I will be interested to see what you find out. I do not seem to have enough power to pull over 2100 rpm in 4th or 5th. And the breaks draging is one possibility. They do not seem to get hot now though. they were hot when it locked up.
I wish that I could save enough to put on disc breaks.

 

[BigRig379]

Have you ever adjusted your brakes?I had a similar problem with my trailer but it was because i adjusted all 4 wheels the same way, didn't realize at the time the threads were different on both sides.

 

[sponaugle]

Have you ever adjusted your brakes?I had a similar problem with my trailer but it was because i adjusted all 4 wheels the same way, didn't realize at the time the threads were different on both sides.

I have not adjusted them, but I will as soon as I get it home.

The question is, would an air pack problem cause both the rock hard pedal as well as the locked rear brakes?

Jeff

 

[rosco]

Sounds like your air pack/booster. A quick way to release the brakes is to crack a rear bleeder screw.

 

[spicergear]

Yes.

 

[Tlauden]

I had the same exact problem as you a little while back, and after reaserching i thought it was the booster, well pulled that off, took it apart, cleaned it, threw it back together and i still had the problem, Next i rebuilt the Master Cylinder, that was my problem part... The piston was jammed and wasnt releasing properly, After a quick rebuild (the longest part was going to the hardware store for brake cleaner to get the gunk outta the fill tank) the brakes worked great!! i can even lock the wheels up on demand now I would just rebuild everything and eliminate your problem, it really shouldn't take two long, i would say 3 hours from start to completely done, then you know your good to go for the trip home!

Although this all depend on parts available to ya.... i got saturn surplus 10 mins away so i guess i sorta lucked out for parts...


Good Luck,
Tyler

 

[rlwm211]

The air pack seems to be at fault but you may still have a problem with your master cylinder.

There is a tiny vent ahead of the main piston in the main bore that vents fluid back to the resevoir when the brakes are released. If this tiny hole is plugged this would serve to prevent the fluid from returning and you would have a creeping brake problem which is what you have described.

I had the plugged vent hole problem with my deuce but in the interest of safety rebuilt the airpack and also replaced all the wheel cylinders and also the master as it was seriously corroded inside and could not be safely rebuilt.

It is quite possible to clog this vent hole when you hone a master cylinder and this needs to be checked before reassembling the master if you do rebuild it.

The test to see if your vent is plugged in the master is harder to do with the remote resevoir. Normally you would remove the cap, and apply the brakes slowly with your hand (air pressure is not necessary for this) and look for an upwelling at the first movement of the pedal and then it stops as the pedal firms up.

I would add that if your linkage is adjusted too tight from the pedal to the master piston, you can cause the same problem. Normally you want about 1/16" freeplay at the master cylinder for the piston before it contacts the plunger from the brake pedal linkage. I think that a little more is probably ok as this seems to get tighter when the truck is warmed up fully. Even so, there is a certain amount of 'wiggle room' in this adjustment, but when there is not enough freeplay, or none or less, you know it immediately because it immediately causes the problem you are having.

Another factor may be the remote resevoir. Is it vented????? This is very important as you cannot displace fluid in a sealed system. The pressure in the remote resevoir may never be high enough to give you cause for concern but a few pounds is enough to activate the airpack and apply the brakes.

If the air pack is not releasing and the brakes are gradually applying it can be one of two problems. One is the compensator bore where the hydraulics are applied to the air valve the piston may be sticking due to corrosion, or gunk. The other is that the airvalve is leaking and applying air to the main piston. In either case once the master is eliminated, you will need to rebuild the air pack or replace it.

I would not automatically change the shoes because of this. The brakes on a deuce are designed to dissapate heat and a lot of it. I would inspect them and look for signs of glazing or cracking and if found, replace them. I would consider changing the wheel cylinders while the drum/hub is off as they are cheap and also that this is a lot of work to change one later on. I paid about $22 for mine each and I am glad I changed them.

There is a good Wagner-Lockheed manual for brake systems for all vehcles at WWW.JATONKAM35s.com in the Deuce TM section about 2/3 of the way down and this has illustrations of how the master works and cutaway views of the ports as I have described them.

Hope this is helpful

RL

 

[sponaugle]

The air pack seems to be at fault but you may still have a problem with your master cylinder.

There is a tiny vent ahead of the main piston in the main bore that vents fluid back to the resevoir when the brakes are released. If this tiny hole is plugged this would serve to prevent the fluid from returning and you would have a creeping brake problem which is what you have described.

I had the plugged vent hole problem with my deuce but in the interest of safety rebuilt the airpack and also replaced all the wheel cylinders and also the master as it was seriously corroded inside and could not be safely rebuilt.

It is quite possible to clog this vent hole when you hone a master cylinder and this needs to be checked before reassembling the master if you do rebuild it.

The test to see if your vent is plugged in the master is harder to do with the remote resevoir. Normally you would remove the cap, and apply the brakes slowly with your hand (air pressure is not necessary for this) and look for an upwelling at the first movement of the pedal and then it stops as the pedal firms up.

It is pretty easy for me to remove the remote reservoir, so I'll do that test before I take anything apart.

The remote reservoir is vented, and as far as I can tell, the level has not changed (other then the bleed I did this AM for a test).

I would add that if your linkage is adjusted too tight from the pedal to the master piston, you can cause the same problem. Normally you want about 1/16" freeplay at the master cylinder for the piston before it contacts the plunger from the brake pedal linkage. I think that a little more is probably ok as this seems to get tighter when the truck is warmed up fully. Even so, there is a certain amount of 'wiggle room' in this adjustment, but when there is not enough freeplay, or none or less, you know it immediately because it immediately causes the problem you are having.

Another factor may be the remote resevoir. Is it vented????? This is very important as you cannot displace fluid in a sealed system. The pressure in the remote resevoir may never be high enough to give you cause for concern but a few pounds is enough to activate the airpack and apply the brakes.

If the air pack is not releasing and the brakes are gradually applying it can be one of two problems. One is the compensator bore where the hydraulics are applied to the air valve the piston may be sticking due to corrosion, or gunk. The other is that the airvalve is leaking and applying air to the main piston. In either case once the master is eliminated, you will need to rebuild the air pack or replace it.

That makes sense, and it sounds like I should eliminate the master problem first. I'll check the free play as well and adjust.

I would not automatically change the shoes because of this. The brakes on a deuce are designed to dissapate heat and a lot of it. I would inspect them and look for signs of glazing or cracking and if found, replace them. I would consider changing the wheel cylinders while the drum/hub is off as they are cheap and also that this is a lot of work to change one later on. I paid about $22 for mine each and I am glad I changed them.

There is a good Wagner-Lockheed manual for brake systems for all vehcles at WWW.JATONKAM35s.com in the Deuce TM section about 2/3 of the way down and this has illustrations of how the master works and cutaway views of the ports as I have described them.

Hope this is helpful

RL

Thanks Tyler for your input, and RL for that great description! I am back in Portland now, and will head back down to Junction City next weekend to do repair and transport.

This morning when I got up I checked a few things, and ran a quick test.

With the engine off, and the air pressure drained, the truck would roll just fine. I opened the rear bleeders just a bit and no pressure at all.

I then fired up the truck and let it build pressure. Once it got to 90psi, I pushed the brakes one time and the truck was stuck. I shut it down and opened a rear bleeder and fluid shot out with a good amount of force.

So on the plus side the problem occurs instantly on startup, and does not require driving around or heat of any kind. As soon as I give it any brake pedal, the brakes are locked 100% if there is air pressure present. Once I relieve all the air pressure, the truck rolls fine again.

Given the above test, does this still sound like the release problem in the master cylinder? I suppose if that hole is clogged, and brake fluid does not make it back into the reservoir there would still be pressure into the air pack, which in turn would push to the brake cylinders.

In either case, given the time constraint and the location I want to go back down there with everything I might need. I'd like to go ahead and purchase a new/rebuilt master as well as a new/rebuild air pack. Is there anything special I need to know to order the right parts? The air pack I have right now is the one with the 'hex head' plug on the side next to the bleed port, not the one with the square plug on the back side.

Do I have to get a replacement air pack of the same kind?

Thanks guys for the tremendous help.... if it wasn't for steel soldiers I would really be scratching my head!

Cheers,

Jeff

 

[rlwm211]

The new style or old style airpacks are interchangeable.

If you can check the problem when you get back try these checks in this order.

Start the truck and build air pressure. Apply brakes. Most likely the problem will re-occur.

First crack the bleeder at the top of the airpack where the hydraulic brake line from the master comes in. This releases the pressure on the airpack in an operational manner and if the brakes release (you can hear them believe me.) then you know it is the master.

If this previous method offers no results, then open the emergency aircock at the back of the truck releasing the air. If the brakes release then it is air leakage in the air pack applying the brakes.

It is possible, however unlikely, that the slave piston in the air pack is sticking and holding the brakes. If this is the case then the only way the brakes release is when you bleed off the pressure 'after' the airpack.

Like all master cylinders the air pack has to return to the "OFF" position (fully return) to allow the fluid to return upstream via the same manner that a master bleeds off via a vent.

Be sure to have a gallon of DOT 5 with you when you start the repair in the field. I would get the brakes working and get home and then at your liesure check all the shoes and wheel cylinders,

Hope this helps

RL

 

[gimpyrobb]

Because the master cyl controls the airpack, I would Start with the master cyl. Also, it is cheaper than anything that has to do with the airpack. My bet will be a blocked compensator port.

 

[sponaugle]

The new style or old style airpacks are interchangeable.

Excellent.. I have a new style on the truck right now, and as I understand it there are not rebuild kits for the new ones. Either way I am going to get a new one to have with me, and if it is possible to rebuild the other one I will have a spare.

I'll also take a new MC with me.

If you can check the problem when you get back try these checks in this order.

Start the truck and build air pressure. Apply brakes. Most likely the problem will re-occur.

First crack the bleeder at the top of the airpack where the hydraulic brake line from the master comes in. This releases the pressure on the airpack in an operational manner and if the brakes release (you can hear them believe me.) then you know it is the master.

If this previous method offers no results, then open the emergency aircock at the back of the truck releasing the air. If the brakes release then it is air leakage in the air pack applying the brakes.

It is possible, however unlikely, that the slave piston in the air pack is sticking and holding the brakes. If this is the case then the only way the brakes release is when you bleed off the pressure 'after' the airpack.

Like all master cylinders the air pack has to return to the "OFF" position (fully return) to allow the fluid to return upstream via the same manner that a master bleeds off via a vent.

Be sure to have a gallon of DOT 5 with you when you start the repair in the field. I would get the brakes working and get home and then at your liesure check all the shoes and wheel cylinders,

Hope this helps

RL

That is an excellent diagnostic list. I spent a bit of time reading over the TMs you mentioned, and what you described makes sense. I thought it was interesting to see in some other threads that some people added a pressure gauge to the brake system ( to see the line pressure I assume), while others made a cab vent system for the air pack. It would seem most of that is not needed in a correctly functioning system, but would be helpful in diagnosis.

Hopefully I'll get an airpack and MC before Friday and head down to do some repair work. It does feel good to get a better understanding of how the system works. Thanks for your very helpful guidance. I'll post back my results!

Jeff

 

[sponaugle]

Recovery Update!

I made it down to Southern Oregon over the weekend and was successful in getting the truck running again!

I started by doing the test procedure outlined by RL above. I started up the truck, allowed full pressure to build, and applied the brakes a couple of times. They quickly locked up, as expected. I then shut off the engine and verified the brakes were still locked. I then opened the bleeder on the airpack, which did not release any fluid or pressure. The brakes stayed locked. I then opened the rear glad hand to release the air from the tanks, and as soon as the pressure dropped the brakes released.

So with that in mind I knew the problem was likely in the air pack. Since I had both a new master cylinder and a new airpack with me I opted to swap both. The swap took a bit longer than I expected. The new master cylinder has three brass plugs in the rear end of the MC. The one on the truck had just the single rear fitting without the additional plugs. This didn’t look to be a big deal, except during the installation those extra plugs on the very rear part made the MC not fit into the small round hole in the frame. This hole normally gives you enough room to slide the MC back and get it up into place. To get it to fit I has to remove one of these brass plugs, install the MC, then put the plug back in. It was also a bit difficult getting those 9/16th MC bolts out as the upper drivers side one is very hidden. If you ever plan to do this on the side of the road, get a 9/16 wobble with a long extension (at least 12-18 inches). That makes it much easier.

The airpack install was straightforward. I had a new style one on the truck, and my replacement was an old style. A few of the fittings were a bit worn, so I’d like to replace all of the metal lines at some point.

I bled the entire system and replaced all the fluid, and on first test the brakes both worked and released just fine. Both of the rear most cylinders leak a small amount of fluid, I assume a result of the very high heat from being stuck on. Now that I have the truck back at home I am going to do a complete brake service on all 6 wheels including new cylinders. Since I have the old parts I will get some rebuild kits and rebuild both so I have a spare of each. ( and know a bit more about how they work internally )

I can’t say thanks enough to all of you guys for the great help. Your wisdom helped me find the right parts to test, and I am very happy to have the truck back at home. If you are ever on Portland RL, dinner is on me.

Cheers,

Jeff