Airpack or master cylinder failure? Both? Neither?

[michigandon]

Spent the last few hours searching and reading many of the older posts/threads, but didn't find anyone with symptoms quite like mine.

Up until today the truck had been stopping fine, however pedal travel was a bit more than I would have liked. Tried do the minor adjustment, and it seemed to have no effect.

Discovered that I had ran over yet ANOTHER nail, so drove to the tire store to have that repaired. On the way home, after some city driving, the pedal suddenly became nice and firm, and the truck stopped better than it had ever had since taking possession of it. Would have been a happy man had it stayed that way, but it was not to be.

After a few more stops the pedal would go soft, then hard again. Stopped in a grocery store and went to leave, pedal went almost entirely to the floor (about 1.5" from the bottom). Put it in low range and tiptoed home. There's enough pedal left to stop at parking lot speeds, but NOT highway speed.

I'm 75% certain the master cylinder has failed internally, but I'm no deuce expert by any means. There are NO external fluid leaks and the master cylinder was full when I pulled the cap off.

Planning on calling/taking a trip to White Owl tomorrow morning, but I would like to to figure out what exactly I'm going to need.

 

[welldigger]

If you pulled the rubber boot back on the master cylinder and it was dry then my suspicion is your air pak is going bad. My guess is what's happening is the seals around the booster piston is allowing air to bypass into your brake fluid. Your MC is the highest point of the brake system so the air travels to it. While the air is in the lines it compresses causing the soft pedal. If given enough time the air would travel up into the MC and bubble out giving you a firm pedal. The more you drive the truck the more air is being introduced which would make your pedal get softer and softer. I believe it is time for an air pak rebuild/ replacement.

 

[The King Machine]

Agree, my truck was having the exact same symptoms. Pitting inside the air pack from moisture I"m guessing.

 

[welldigger]

I guess I should have clarified a bit more. Tho pitting is VERY common in the air end of the air pak that isn't the direct problem. There are several seals around the shaft of the piston that keep air out of the brake fluid and brake fluid from leaking into the air end. These seals sound like they are worn enough to allow air in but not quite worn enough to allow brake fluid into the air side.

 

[bigmike]

I agree. I just replaced the master on my M543 and I had good brakes. I let it sit for a couple weeks, start it up and POOF, no fluid in the master and no brakes. I'm going to replace my airpack.

 

[silverstate55]

That's the same problem I'm having with my Deuce currently, and need to rebuild the Airpack. Mine actually gave the hard pedal and caused the brakes to drag!

 

[peashooter]

Where have you guys found the best source of a quality airpack rebuild kits? Do the rebuild kits tend to be chinese now as most other new replacement seals are? If so are there any known US made kits out there currently?

 

[welldigger]

Where have you guys found the best source of a quality airpack rebuild kits? Do the rebuild kits tend to be chinese now as most other new replacement seals are? If so are there any known US made kits out there currently?

Depends on which style you have. For the older long style there are many sources. Just shop around and see who has the best price. The short style is a bit harder to find. Tnj Murray has the rebuild kits and another member here tracked down a slightly cheaper source. As far as country of origin for either kit I honestly don't know.

 

[sandcobra164]

Just my 2 cents on airpacks. I had a long style that had long been abused by no one draining the air tanks after a run. When I first got the truck home, I drained the wet tank and could have likely watered my garden with the amount of water that came out. My truck had a very hard pedal, it got a little easier when I oiled the back side of the piston. I've now installed a "short" airpack and my goodness what a difference. I push the brakes about as hard I do my regular truck which is not hard. It'll lock the back axles on pavement with a robust push. The short airpack may get some nods against it but if you look, it has a larger piston on the air engaged side that's "helping" and to me requires lower pedal pressure. I bagged my long style one up and gave it away at a Rally. Sure, it's rebuildable for a cheaper price but if you keep you're brakes adjusted and not leaking, I think the short style is the way to go. Of course, I have an extra just in case and for anyone curious, it was a bolt in replacement. No fab work needed.