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Can't seem to get much stopping power, soft brake pedal. Our setup is as follows: Disc front , drums rear, booster and master cylinder under floor. Prop valve, 2 lb. residual valve to front, 10 lb. residual valve to rear. Have bleed brakes and master cylinder 3 times, no air in line. A mechanic friend said to try separate lines to the front disc's, presently have one line with a T fitting to send fluid to both front brakes. He also said maybe an adjustable prop valve to the rears. Anybody have this type of brake pllumbing? Or any suggestions on what we can do. Thanks Frank

I have similar but booster/master on firewall. I had problems until I went with a master with a larger bore and put an adjustable prop to the rear. I have the front disks t'd as well. I have a ton of stopping power but pedal always feels a little bit soft. 1000 times better now than when I had a mustang master cylinder on it though.

good luck.

Several things I noted when setting up my front discs/rear drums....if you're trying to use a conventional prop. valve, whether salvage or new it will complicate getting a complete, airfree system. Secondly, the adjustable prop valve should go into the rear circuit along with, but in front of the 10# residual valve.

I see no practical reason to seperate the front disc lines. Having set up a number of this combination, I quickly learned that the factory or salvaged multifitting prop valves were the cause of most, if not all of my bleeding problems.

I'll add that it is important to have the rear brake shoes properly adjusted and that sometimes you have to give the calipers and wheel cylinders a tap to dislodge stubborn air bubbles.
I designed my system so that I could adjust my brake bias from inside the cab. Have some pics in my webshots "shoebox" album. Having a firm pedal and well balanced brakes should be a priority. Hope this helps.

Dave

Frank,
Do you have a single or double diaphram booster?
Some of the smaller boosters that the aftermarket guys sell only have about 300 lbs of assist. You need much more than that. I would recommend a 8" double diaphram booster, corvette MC, with a proportioning valve. I have been using this set up on my 56 3100 for six years with no problems.
Fred

It is a corvette mc, don't know about the booster though. We have a prop valve on it also. I may break down and take it to a mechanic. It has been driving me nuts the last 2 weeks. The brakes worked fine for a week. We have bleed them 3 times so far without success. Thanks for the response, though.

Aren't Corvette master cylinders for disc/disc set ups? Thought maybe with not jiven' with the rear drum thing...maybe...

One of the best sources for these conversions is ABS in Orange, CA. They also have a shop where they install these conversions so they have real world experience. The conversions using Corvette MC's can be set up for disc/disc or disc/drum and with residual valves.
These guys can tell you what type of a system is best for your vehicle.
Fred

I had a recent brake problem where the brake felt spongy, light and I couldn't get the full brakes I should have. I found a flexible hose was broken on the inside. The outer layer of the hose collected the brake fluid (like a baloon filling with water) when I pressed the brake pedal. When I let off the brake the outer hose would have enough pressure to push the fluid back into the system. No leaks. Replaced flexible line and now it's AOK.

Unless they sent the wrong MC, it was a corvette disc/ drum MC. I appear to not have any leaks from the lines. I have vacumn as I checked that out. Maybe it is a bad booster? Not sure at this point.

If it worked great for a week or so and then went bad, I have a hard time thinking that you have a wrong part (as you mentioned earlier). Keep thinking simple.

Usually the hardest things to figure out have the simplest solutions.

Have someone hold the brake pedal down tight and then the secong person goes around and inspects the flexible hoses for bulging first. That one baffled me for a while on one of my vehicles.

You also said you have bled the brakes several time and the same effect. Try taking the lines loose at both ends and blowing compressed air through the lines and valves in the "reverse" direction the fluid flows when pressure is applied. There could be an obstruction that blocks one way but not the reverse.

Replacing parts to find the answer to the problem gets expensive. Know how these things work instead of just how they go together.

Good luck and let us know what you find.

Anybody know the year / application for the Corvette master?? How about the 8" dual diaphram booster??

My vette master is '78, running disc/disc pretty well. When I did mine I had the same problem, now that I think of it. No matter how many times I bled the system the pedal was soft. Turns out it was the speed bleeders. 2 out of 4 were junk, there was some metel shavings/debris from the new lines I did not get out jaming them up. I don't know what you have but it might be worth checking?

Frank,
Does your setup have an adjustable rod between the pedal and the m/c. It may need to reset or lenghtened a bit.

Yes it does, Wilbur. That was the next thing I was going to try. Thanks for the suggestion. Haven't had time to work on it this past week. If I lengthened the rod, would that give me more pedal?

Wilbur, You hit it on the nose. I had to adjust the rod between the m/c and the pedal. I also bled it with the front higher than the rear, tried using some gravity, got that nasty air out. Thanks for all the suggestions. Didn't get to work on it much this month till this weekend. It stops great now!!!

Make sure the vacuum line is hooked directly into the intake manifold.I have been using an aftermarket on my 55 with no problems,it is disc front drum rear.

It sounds like you got your problem corrected...

I've found that when building a "restorod", if you use the entire brake system out of the same (type of) donor vehicle, you dont usually have many compatibility problems...