Brakes: Hydrovac rebuild. No pedal

[Studejohnn]

Been chasing problems since acquiring the Champ. Brakes again. Some background. Went through brakes about four months ago. New wheel cylinders on all four drums. New hoses. Flush and bleed,and brakes were good until about three weeks ago. Went for a drive, bam, pedal right to the floor. M/C chamber was empty, but no visible leaks. Removed the hydrovac (type a) and brake fluid poured out the vacuum intake. Brake Systems Inc. in Portland said they found gas in the unit. After the rebuild (and it was pricey), I can’t get a strong pedal. Vigorous pumping gets a soft pedal about three inches off the floor, and it fades away quickly.
I bled the top bleeder on the HV first, then the bleeder on the slave, then all four wheels. I just don’t see how air can be trapped in there somewhere.
Next I disconnected the brake line feed from M/C at the HV, and capped the line. The pedal was at the top and hard as a rock, and no fade out. I though my rebuild of the under floor M/C might have gone bad.
After searching a bunch of threads, I found a comment from Bezhawk and wonder if this might be the problem. Bez noted that two check valves are not needed in a disc brake system. I wonder if the same applies to drums all the way around. The HV has a check ball in the slave cylinder, as does the M/C. I remember installing the new check valve in the kit.
I know the next step is to remove the HV, turn it upside down, and see what comes out.
Anyone have some ideas about this before I do that?

[E. Davis]

Sounds like a problem with the hydro-vac to me. The old pro's tell me you should bleed the hydraulic end of the hydro first (slave cylinder) and then the top but I can't see where that would make any difference in your case. Probably something wrong in the rebuild. Again, probably nothing to do with your case but I have replaced two hydro's and each time I had to readjust the brake pedal free play to get a full pedal. They say 3/4 to 1 inch free play but I usually adjust the pedal travel that is comfortable for me and still allows the M/C to function as it should.

[Jeffry Cassel]

Hydrovacs a a bugger to bleed! Brake fluid seeks its own level and with an under floor mc, you are constantly trying to pump it uphill! When you have symptoms you describe, it almost always means air in the system. I bought a vacuum bleeder once: it did not work at all, but that might be the best way to bleed these systems---if one can be found that actually works. Yes you need a check valve. Is the mc good??? Are the lines all good?? When the Hydrovac failed on my 58, brake fluid went thru it into the intake (brake fluid burns white!)

[E. Davis]

I use a pressure bleeder and it works well. Jeffry is right the hydro vac contains a lot of air and it takes a little while to push it all out. Never had any luck with vacuum bleeders. Nothing works likes pressure pushing the fluid and air out.

[Hawklover]

I use a pressure bleeder and it works well. Jeffry is right the hydro vac contains a lot of air and it takes a little while to push it all out. Never had any luck with vacuum bleeders. Nothing works likes pressure pushing the fluid and air out.

Please tell me about the pressure bleeder you use, would like to purchase one myself.

[E. Davis]

Go to U-Tube and they will show you how to make one from a one gallon weed sprayer. Mine cost less than ten dollars to make and works great. You will have to fabricate a connection to your master cylinder cap. I had one from an old M/C that I drilled and put a fitting in to slip the plastic tubing over. A friend of mine used a metal air valve stem available at any tire shop for his and when he is finished bleeding he just puts a valve cap on it to seal it and that works okay also.

[Studejohnn]

Thanks all for the replies.

I have adjusted the m/c rod out a little and gained a little pedal. Still needs three or four pumps before it will come up. From what you guys are saying, it could be air in there somewhere, even after 3/4 of a quart of DOT 3. I’m getting firm streams of brake fluid from both bleeders on the hydro and the four wheels. No leaks that I can see. m/c solid.

I’ll look into pressure bleeding. That’s something new to me. In the meanwhile, I’ll drive around the neighborhood, slowly, and see if that helps.

[E. Davis]

Sounds to me like you have it bled. The problem may be in the pedal rod. When I adjust mine to have a good pedal with about 7/8 of inch free pedal I turn the rod into the MC until about 3/4 of an inch of thread is showing behind the lock nut on the pedal rod You can adjust the rod in to the MC until you get the amount of pedal you want until it starts to not release the brakes and you can physically feel the drag. Kind of hard to explain and this is from my personal experience with my car so I hope I don't draw the ire of some contributors. Trial and error will eventually solve your problem.