Street rod has 1984 Corvette rear end with dual piston calipers and Mustang II front end with disc brakes. Master cylinder and booster are new parts manufactured for street rods and are integral and mounted under the floor. There is a block in the plumbing that I believe is a proportioning valve. As far as I can tell there are no residual pressure valves in the system. Car has always had a very low pedal and I started bleeding the brakes to insure that was not the problem. First brake that I bled (right rear - farthest from the master cylinder) showed air bubbles when I started bleeding (Using clear plastic tubing submerged in jar of brake fluid). After bleeding 3 pints of fluid through this one brake I am still seeing air bubbles in the fluid. I had heard that these Corvette discs were difficult to bleed - is there a trick to this??
There also seem to be differing opinions on need for residual pressure valves - are there any systems operating succssfully without them?
Thanks
Don

If the master cylinder is mounted equal to,or lower than the level of calipers,you will need RPV's. One of the reasons you are still getting air,is the method you are using to bleed the brakes. I have found that using the old hose in a jar of fluid trick,allows some air back into the system,thru the threads of the bleeder screw.I am assuming you did a proper bench bleeding of the master cylinder before you installed it on the car?? If so,try having a friend pump the pedal for you while you bleeding them.
--
Everyone should believe in something...
I believe I will have another beer...

You have my sympathy. I took my '76 to a "reputable" shop to have stainless calipers put on the rear end and they couldn't get the air out of the system, causing me to nearly get killed on the way home. the next dayI had one of my students use a power bleeder and he got it right the first time! I remember seeing an article in Car Craft (if I remember correctly) on how to construct a power bleeder for your home shop out of inexpensive parts.
--
docchevy Remember Physics explains everything!

From my mechanic:

Hello, a friend Alan asked me to try to help you get a pedal. A system that keeps pushing air through it has to get it from somewhere. One direction leaks are rare but not unheard of but you may also be picking the air up at your connection to the caliper. Does this happen at any other caliper on the car? If not it maybe a piston seal at that caliper. You also should have a Vette master which has integral residual valves for the front and rear which can prevent the calipers from picking up air by having positive pressure at the caliper seals. Corvette calipers are very efficient pieces but at a cost of complexity and they are also sensitive to water contamination which can cause corrosion in the piston bores and leaks. Any true performance car has similar calipers. Brake fluid has a very high level of hydrocicity and picks up water like sugar draws Yellow Jackets. I don't know the condition of your calipers but you can get rebuilt ones with stainless steel liners ! and then run silicone fluid (DOT 5) which pretty much makes the calipers last forever. That again has its own cost, it makes the pedal a bit spongy but you can make up for that with braided brake lines. Corvette calipers are not the best with lack of use. When they sit for long periods they sometimes start to drip but then you pump them a couple of times and they seal up and work fine but not always. I believe this is caused by the residual pressure easing off and letting the seal relax and collapse. There are also brake rod adjustments that may need to be done which would give the same low pedal but that still will not be the source of the perpetual air. Hope this helps and you can call my shop at 845-371-2148 if you need to. Dean

--
1937 Chevrolet 2 door Master Deluxe 2 doorsedan

1940 Chevrolet 4 door Special Deluxe

Texrodder I have had the exact same problem as you and I solved it myself with much anxiety. First if your master cylinder does not have the residual valves you will need to install them on your brake lines as close to the master cylinder as possible. Jegs and Summit have them. Use the 2 pound for disc brakes. I have tried every bleading method there is and on my car a $6.95 one man blead kit has worked the best. This is a clear hose with a recovery bottle, designed so that you do not have to close the bleader valve when you let up on the pedal. The trick is to place your recovery bottle HIGHER than your caliper when your bleading. Keeping your master cylinder full, pump the pedal up and down slowly with the recovery bottle up high. You do not have to close the bleader valve each time the pedal comes up as you do with the conventional method. If there are no leaks in your system your caliper will normally blead out with about 10 to 12 pumps depending on how much air you have in the system. Start with the longest brake line and work to the shortest. If you have two bleader screws on one caliper, blead the inside one first, then the outside. Hope this solves your problem.

One other thing, you might check the hole in the floor board to make sure it is big enough to allow for the full travel of the brake pedal. I have seen some cars that the floorboard would stop the pedal. It felt like the pedal had bottomed out when it had not. Check it close with a good light.

Are the bleeders on the caliper at the highest point? If not, make sure they are or you'll never get 'em bleed.
--
Fred aka ZZFord or 33Highboy