The Stovebolt Site Forums The Shop Area Driveline Master cylinder

I have replaced all my brake lines and two wheel cylinders. I have rebuilt the other two cylinders and the master cylinder. My brakes still do no hold pressure. After a couple pumps they hold, but then if you let off, in less than a minute the pedal will go back to the floor as soon as you step on it. I have fixed all the leaks I could find and bled the brakes several times now. Is it possible my master cylinder is bad but not showing signs of a leak? Maybe my problem isn't air in the system but just a bad part? Seems like a pretty simple system but I cant figure this out. 1950 3100 Chev.

Do you have all the shoes adjusted up? If not, you should do that before proceeding. If you had a gap of say around .10 " between each shoe and the drum, you would use up all the travel in the master.

If shoes are good, as said. It really does sound like MC so far. Revisit the assembly sequence of parts again. Take it out and inspect inside. Rubber installed in correct direction and so on.

Been there for sure. I found a sequence if you like that works.
1, Adjust each brake shoe at each wheel until it just touches the drum.
2. Bleed each wheel cylinder starting with the right rear, left rear, right front, left front.
3, Wait, yep wait for about 1 beer, or what ever seems like 10 minutes.
4. Try that pedal. If good, repeat step 3 and smile. If it still is soft then pull the MC and see what you have.

Have you adjusted the pushrod that goes into the master cylinder?

I will revisit the brake shoe adjustment and go from there. I have not even thought of adjusting the push rod. I could play with that also. One of my considerations is I already need to order a new water pump and NAPA can also get me a master cylinder. I don't want to spend that money on a part I don't need but I have a 20% off coupon good till the end of the month so if I do need one now is the time to order and save a little cash.

You probably havn't got the shoes adjusted right. The huck brakes have 2 adjustments on each wheel. You can tell which way to turn the adjustment by picktureing the cup on the ends of the wheel cyl. They are all right hand treads. Adjust each one till you get a heavy drag & back it off 4 notches. There may be some drag in it yet but will smooth out when they get seated in.

The TF adjustment on the MC is just a cammed bolt. Must not take much to make a big difference.

What did it for me when that happened years ago was bench bleeding the MC first. Sounds like the lower MC has air in it.

I think I found the problem, or at least a problem. Not sure how this was hidden so well before but when I was adjusting the front left shoes I looked over and happened to notice a drip from user the master cylinder with every few notches. I crawled under and found fluid was escaping backwards into the boot over the push rod. I believe I probably tried to rebuild a cylinder that was just out of limits and its time to break down and replace it. I will pull it part and check to see that I put it together correctly first. Either way I appreciate the advice as always and will follow the sequences of events posted here and hope that I get it taken care of. Its ready to drive after this.

Good catch. That boot can hold a lot of fluid. At least you were looking and thinking. That is most of the battle.

I believe if MC was not pitted/scored/rusted and you just soft reamed it, it would not be out of spec. The rubber does not wear steel. Replacing it using your discount would not hurt either. The last one I built (TF) I had to assemble backwards to what instructions said. I could not load it into the end shown on instructions.