Give me a brake! opinions please (UPDATE)

[Kaiserjeeps]

Drove my Duece in a parade on Monday. On the way home (20 miles) my brakes started dragging. I forgot my temp gun but the hottest drum was the passenger rear. I could touch all the others.
Got home and the rear pass wheel was smoking from brake drag. I cracked the bleeder and about 3/4 cup of very hot brake fluid shot out under very high pressure. It was very foamy and looked like it was boiling.

This problem is intermittent and does not do it unless I drive for quite a awhile.



The airpack and master cylinder were rebuilt to convert back to DOT5 in 2004. The wheel cylinders were also rebuilt in 04 mid year.



When I feel the drag, my master cylinder pushrod seems to be sticking in the master cylinder. I can feel the slop under the pedal. Almost like a clutch pedal with free play. Sometimes the pedal is all the way up and very firm. When I have the problems it has the free play I mention.



When applying the brakes hard, it takes several seconds (4- to release and roll easy.



This happened on my last long distance parade. ALL the brakes bound up with pressure. Bleeding a wheel cylinder down got me home. Lots of pressure there.



I am leaning towards the master cylinder because it feels like it is sticking.



What do you guys think. Could it be a bad airpack since it is making pressure somehow? Or do you guys think the master is not functioning correctly?



BTW, the parade was a blast. Oregon's second largest parade in the state.



Thanks for the input on the brakes. I could shot gun it with new parts, however money is short and I would like to make it safe with out breaking the bank. ... Al.

 

[cranetruck]

Glad you were able to enjoy the parade!
You don't have to rebuild the air-pak or MC to change brake fluid, there must have been another reason.
The air-pac has a vent line, which is tee'd with the vent lines from the MC and the fuel tank. Make sure it is free and clear. I actually separated mine completely to keep fumes from mixing from fuel tank etc.
To test the air-pak when the brakes lock up, open the service connection (driver's side) at the rear of the truck. When it is open, air will be released from the air-pak and that will release the pressure on the wheel cylinders when all is working as it should.
If nothing else, this may be a starting point for you.

 

[Gatnom]

Kaiserjeeps: Here are couple links to posts about similar touble. You'll have to scroll them to the top to read the whole discussion. Hope you get it sorted out. Dave



[color=#ffff00>[url=http://www.steelsoldiers.com/DotNetForum/default.aspx?f=43&m=20654&g=20698#m20698]http://www.steelsoldiers.com/DotNetForum/default.aspx?f=43&m=20654&g=20698#m20698[/url]

 

[Recovry4x4]

Well KJ, you've probably diagosed our own problem and just didn't realize it. There is a compensating port in the master cylinder. This port allows the return of fluid back into the master cylinder upon release of the brakes. If the piston is not allowed to return to it's seat completely, the compensating port will be blocked and the brakes will creep up on locking up. I inherited the same problem many years ago on a Jeep we were working on. The other brake techs put 4 or 5 pairs of calipers, several brake hoses and 3 or 4 master cylinders on this Jeep and couldn't quell the problem. What happened was the original tech couldn't get the pedal as high as he wanted so he extended the pushrod between the pedal and the master effectively pushing the piston from it's seat and blocking the compensating port.

 

[ken]

Some times the airpack may stick. Have you drained the water from the air tanks? If there is too much water in the air lines the water will cause rust on the inside of the air pack. Some times they won't work, and some times they won't release. If it turns out not to be the master cyl, then you may need to dissemble the airpack to clean and relube it. Some people use a light oil. But everyone i have taken apart had white grease for lube.

 

[Kaiserjeeps]

Thanks guys. I drove it again last night. The brakes take several seconds to release. I changed it from dot 3 to silicone dot 5 which is the reason for the rebuilding of all components. I think it is the master cylinder. I'll pick up a kit and go through it again. Probably need brake shoes now that I have driven with them on so long. Every time it has done this it has been a long ways from home. Kind of throws a dampener on a day. At least I can bleed it off. I'll take a closer look at the things you guys mention. Thanks for the feedback and the links. Al.

 

[Kaiserjeeps]

Cranetruck, I just reread your post. Do you mean open the gladhand trailer connection port at the back frame crossmember?
I think thats what you mean. I guess that would be an easy way to tell if it had pressure. I just want to make sure I understand you correctly. So if there is any pressure or air flow with the truck at idle and nothing on the brakes, that sounds like a bad airpack?

 

[Stretch44875]

I had the same problem on my old willys jeep, the port in the master cylinder was blocked with rust. Put another master on and was good to go.
Dennis

 

[Kaiserjeeps]

I tried something last night. I pulled the trailer service gladhand cover off and mixed some soapy water up to see if it made a bubble while running. As far as I understand there should be NO pressure there until the brakes are applied. Well, I had quite a noticeable bit of flow at idle. So from what I can tell my airpack is bleeding by applying the brakes little by little.

Does anybody know if there is any pressure at all at the trailer brake connection with out the brakes being applied. I would think none should be present. Just checking and still very interested in opinions. I have no experience with air over hydraulic brake systems.

 

[Gatnom]

Kaiserjeeps: Not sure of the answer to your immediate question, but if you check out the second link in my above post, you will see that you can check if the metered air supply is leaking through by disconecting the line to the back of the can on the air pack. There should be no air there unless you're on the brakes. Let us know what you find out! Dave

 

[Kaiserjeeps]

Thanks Dave. I did look at the links. I want try what was mentioned this weekend. I was getting into it last night , then the girlfriend showed up. She looked like alot more fun so once again the truck waits for me. LOL.

 

[rdixiemiller]

Girlfriends are like that. They look like more fun than trucks.
Looks are deceiving.
Men are stupid.
We tend to want to upgrade Girlfriend 2.0 to Wife 1.0.
It's about 1 year after you upgrade Girlfriend 2.0 to Wife 1.0 that trucks look like more fun.
After another year, you know trucks are more fun.
After 22 years of Wife 1.0, you're damn certain that trucks don't complain as much as Wife 1.0 does.
Trucks are cheaper.
Much cheaper.
If you never upgrade to Wife 1.0, you can have many more trucks.
Trucks do not care if you look at other trucks.

 

[Gatnom]

If anyone knows of an Air/Hydraulic circuit diagram for the AirPac hidden in the TM’s, I’d sure like to know where it’s at. I’ve searched with no success. Thanks: Dave

 

[Kaiserjeeps]

rdixiemiller, LMAO!!!!! And Dave, Big ditto!

 

[Gatnom]

Still no luck at finding an Air/Hydraulic circuit diagram anywhere, but I was able to verify that the Trailer Air (drivers side glad hand) comes from the metered air supply and only gets air when the brakes are applied. Guess I won't have to crawl under the truck and remove a line to dump the air next time the airpac sticks! Always learning! Dave

 

[cranetruck]

Here is information from the 1956 TM9-8000.

 

[cranetruck]

Note that the piston within the hydraulic cylinder on the airpak (slave cylinder) has a valve in it that will allow the pressure from the master cylinder to operate the brakes with or without air pressure.
Also, note the bleeder valve on the airpak. When bleeding the brakes, do this one first. You can reach up and operate the brake pedal from below when bleeding this one.

 

[Kaiserjeeps]

Thanks for posting that. I hope to dive into it soon. It's bugging me not haveing a truck that is 100%.