The Stovebolt Site Forums The Shop Area Driveline Brake Help Needed

I'm a newcomer here, and a new owner of a 41 Chevy 3/4 ton pickup that I plan to fully restore (my first restoration). One of my first tasks is to rebuild the brakes. I've installed new brake hoses, shoes, wheel cylinders, and master cylinder. I bench bled the M.C. before installing. I've bled the brakes until no more air is coming out. I see no leaks in the system anywhere. The shoes/wheel cylinders have been properly adjusted. I can pump the brake pedal several times and the brakes are solid as long as I hold pressure with my foot. When I let off on the pressure for a few seconds and then press the pedal again, it goes to the floor. Why is the system not holding pressure? Any help/advice would be appreciated.

You either still have air in the system or they are not adjusted properly. I got a hunch it's the later. The huck brakes are hard to adjust. There are 2 adjustments on each wheel. They are all right hand threads. If you put it together your self you can visualize which way to turn each adj. Tighten one at a time till you get a heavy drag. Then back it off about 4 notches. If there is still some drag its OK. Do all 8 this way & I bet you will have a good pedal. They are not right till the pedal is right at the top & you just apply pressure to it. Make sure you have a small amount of freeplay in the pedal till it contacts the master cyl. piston.
There is another Stovebolter having the same problem. See "master cyl. woes." Maybe he will tell us how he came out.

Hy summerfi, welcome, does your truck have a hydrovac power booster by any chance? If it does you have to bleed it first, other than that it sounds like you did everything correctly. Good luck, and please keep us posted.

There's no hydrovac power booster, and I'm pretty sure I have the brakes adjusted correctly. I adjusted each side of each brake until there was drag, and then backed off slightly. The only other possibility I can think of is if there is an air leak somewhere in the system, but if no fluid is coming out then I wouldn't think any air could be getting in. Thanks for the suggestions and keep 'em coming please.

Air gives an unmistakable springy feeling and you won't get a firm pedal with air. I would try adjusting the shoes so that they are right on the drums and try the pedal. If that doesn't make the difference than there is a problem with the adjustment of the master cylinder.

Summerfi,
If I understand your situation as described in your first post, I had similar results when I completely rebuilt my brake system on my COE (with hydrovac). I adjusted the brakes, bled them, then got the motor started which would then supply vacuum to the hydrovac booster. When the beast moved under its own power for the first time in two years, the brakes were disappointing, as I had to pump them a couple of times to get them to actuate. I bled them again, to no avail. In desperation, I adjusted them again, found them way off, and then when I tried the brakes after the second adjustment, they were great. I was told later that the shoes needed to be centered, to get to final adjustment. Thus, I agree with Truckernix and would suggest you adjust them again and see what happens.

Kent

This is an update on my original post. I've re-adjusted the brakes until I can hear all the shoes lightly scraping the inside of the drums. I've bled and bled and re-bled the lines until I'm very confident there is no air left in the system. The problem still remains. To summarize, I have to pump the brake pedal to get any brakes. Then, as long as I hold the pedal tightly down, the brakes remain firm. But, once I let off on the pedal, within a second or two I have no brakes again...the pedal goes to the floor when pushed. To get the brakes back, I have to pump the pedal again. I've noticed one thing that I think is a clue to the problem. If I don't let the brake pedal quite all the way out, so that the push rod on the master cylinder doesn't ever come completely out to its maximum point, then the brakes remain good. But if I let the push rod come completely out as far as it will go, then I lose the brakes. It is a new master cylinder, so I thought perhaps it is defective. I replaced it with my old one and the exact same thing happens. It almost seems like I need to shorten the linkage to the push rod so that it cannot come all the way out, but there is no way to do that. Any ideas?

Forget that "lightly scraping" bit. Tighten them till you get a heavy drag both adjusters on each wheel for the time being. Then see what kind of pedal you have. If it is good then back the adjustments up about 3-4 notches each. If not you may have put something together wrong. DON'T adjust the pushrod till all the play is gone. Serious problems will result.

Well, Wrenchbender, I gotta hand it to you. You were right. I adjusted all 8 shoes so they have a heavy drag on the drum, and now the brakes work fine. Problem solved. I'll back them off just a tad and then should be good to go. On to the next task....cleaning out the cooling system and replacing gaskets and hoses.