Brakes LOCKED UP HELP!!!

[vinny-socom1]

My brakes are locked up on my truck?? I've tried to diagnois this but can not find the problem, please I need help I'm trying to make it to the FL Rally and really want to take the truck. I notice the brake peddle is hard as a rock when this happens, I've got air coming from the drivers side rear(emergency right) air valve when opened?? I figured my air pack was locked up right?? well I change it today and it has not changed. I have noticed my MC is leaking but not sure if that would cause it? If I bleed the MC it seems to release the brakes and move freely but once I hit the brakes a couple of times it locks up again? HELP!!!

Vinny

 

[poppop]

Emergency side has air all the time when air is in the tanks. The only times I have had this happen on farm trucks the return port in the MC was blocked or for some reason the MC piston was not returning back far enough to open the return port. I recently rebuild the MC on my dump truck and adjusted the push rod to shorten Petal travel. When the truck warmed up I had it to tight and the brakes locked up. Back it off some and they worked fine. Have you pulled the MC recently??

 

[vinny-socom1]

No I have not done any work on the MC it leaks so I know I need to rebuild it, sorry I was talking about the drivers side air valve, emergency is the right side. I thought the drivers air valve only has air when the brake is pushed correct?

Vinny

 

[poppop]

The service side only has air when the petal is pushed. The farm truck I had trouble with got an obstruction over the return port and would not let fluid return. It happened on a trip and when the brakes locked I had to loosen a bleeder screw on any wheel to relive pressure. It worked fine until pressure built up again. I don't know if the air-pac could be the problem or not. But its sure that for some reason fluid is not returning when you release the petal. I hope you make it to the Rally as I will not be able to. Recent Hip replacement has me not driving anything with a clutch for five more weeks. I really hate missing all the fun.

 

[vinny-socom1]

OK which line is the return line? one on the front of the air pack or bottom.

Bugei -I know the air pack is good as I pulled one from my other truck that was working fine and I still had the same problem.

I figured the airpack was not releasing but I know thats not the problem now, If I bleed the the system by the airpack bleeder the brakes release but a couple of pushes on the pedal and there locked up again.

Lloyd do you think the MC is the problem? it leaks really bad when you push the pedal.

Vinny

 

[clinto]

I will bet dollars to donuts that is a bad airpack. I'd wait for someone more experience to chime in, but if it were me, I'd get an airpack rebuild kit ordered PRONTO and get the airpack out on the bench and cleaned up.

 

[vinny-socom1]

Clinto I swapped the airpack already and I still have the same problem? The truck I pulled it off ran and drove fine so I think my problem is somewhere else.

Vinny

 

[clinto]

Please ignore any future advice from me!

 

[dm22630]

Do you think that you could have kinked a line somewhere when you installed the M109 box?

 

[Recovry4x4]

My diagnosis from afar! I'm pretty sure Lloyd is right. The master cylinder has whats called a compensating port. This port allows BFS to return from the system to the master cylinder. Soldier A or Soldier B was probably having a fit with a low brake pedal and adjusted up the pushrod nice and tight. This works OK for a while but each allpication of the brakes adds more fluid to the system and subsequently locks them up. A faulty airpack can do the same but you already changed that. The only other thing in the entire system that would cause dragging brakes would be rubber hoses with a flap inside, the symptoms you describe doesn't mirror that problem.

 

[BEASTMASTER]

my 5 ton did that a couple times, once in the 4th of july parade. had to put it in low range to move, and it stopped by itself. the m/c had crap in it , not letting the plunger return. replaced the m/c and been fine ever since.

 

[vinny-socom1]

Kenny which line should I pull and can I just shoot air thru it once removed? could the problem be internal with the MC? I only ask because I drove this truck from NC towing another with no brake issues and all over since then.

I had no air lines that would be close to the 109 box so I know that clear.

I didn't know if one of those small air valves could cause this? I have bleed the truck a couple of times and I have good fluid movement so I don't think I have a bad rubber line right?

Vinny

 

[vinny-socom1]

Beastmaster I think you might be on to something, mine was dry a couple of times since it leaks at the shaft.

Vinny

 

[Recovry4x4]

Crap could cause the piston not to return and subsequently the piston blocked the port. CHeck your pushrod adjustment You can't really blow it out.

 

[vinny-socom1]

I think I will pull the MC on my other truck tommorrow and swap it out and I hope that fixes it!! I don't think I can get another MC or rebuild kit in time for the Rally, but maybe if someone has one I can buy at the Rally and rebuild it then....

Vinny

 

[Recovry4x4]

The MC swap will fix it.

 

[dm22630]

I had no air lines that would be close to the 109 box so I know that clear.

I was talking about a brake line....not an airline. If one was kinked....would that lock up the brakes?

Are all of your wheels locked? Have you jacked the truck up off of the ground to see if any spin freely?

Just a thought....

Good luck!

 

[vinny-socom1]

Yes, all of my brakes are being applied thats why I thought it was a sticking airpack but when I swapped it out and I still had the same problem I knew I was missing something.

Thanks dm22630 I like the questions because some times it just helps having a second set of eyes & ears if you know what I mean.

Vinny

 

[BEASTMASTER]

hey , if you're gonna swap the m/c take it apart and clean it, put it back together. rebuild it at another time.

 

[timntrucks]

vinny this very thing happened to my duece. 73m819 told me to drain all the air from the sytem if i remember right and they pump brakes with no air. you might want to pm him to get the straight of it. i did whatever he told me to do and it worked and is still working ot was all in the air. Tim