I've been working on the comet and the brakes have been giving me a little trouble. Fronts are 03 cobra disc and rears are explorer disc. The master is from a 1974 maverick manual disc/drum and drum/drum proportioning valve. I added an adjustable porp valve for the rears. My next step is to gut the stock porp valve. Master has been bench bled and is a known working master. The issue at hand is it takes about a half dozen pumps to get some pressure built up. After you let go of the pedal and wait a couple seconds the pedals goes back all the way down. When I was bleeding the front brakes and I removed the initial pressure the pedal went down like normal, I had the wife hold the pedal down and I was able to spin both rotors pretty easily. I've heard of many people using the maverick master on disc/disc cars because of its bore size. I've bled the brakes quite a few times already, could there still be air in the system?
I had a master that wasn't very old give me fits like you're describing. Had to pump it repeatedly to get pressure. Bled the brakes several times. Ended up changing it and solved my problem.
I already swapped another new master but I couldn't get that master to bench bleed so I used one that was good. I'll return the new one later and get another new one.
I haven't bench bled one in years... Now days I use a hand vacuum pump to pull the fluid out the bleeder valve at caliper/wheel cylinder, did exactly that when I installed the disc brakes on my Comet... Pedal height is exactly where it should be and there is no sponginess...
If you have the rear passenger caliper mounted like mine is (up side down) you need to take it off and flip it right side up then bleed, that will fix the issue, let us know
After several different mc's i figured out the plastic brake switch is leaking on the combo valve. I'm going to remove the combo valve and run tee for the front and straight for the rear directly to the mc. Should fix the problem. Since I'm running 4wdb I'll be fine.
Well I still have a soft pedal. Replaced the master and took out the combo valve. Reflared the brake lines and found no leaks but I'm still getting a soft pedal after building up a little pressure and letting the pedal back up for a couple seconds.
I went through the same thing, like 5 different MC's then finally removed the passenger rear caliper, turned it upright bled the brakes and put it back on, then it would stop on a dime! end of problems! I don't know if that is your problem but you must turn the right rear caliper right side up to bleed it.
Maybe the master can't supply enough for the 4 pistons in the calipers? Maybe find a 93 Ranger master.
Are you still using a disc/drum MC? With all discs you would not want a residual check valve that is probably built into the MC for the rears. Disc/disc MC with matching proportioning valve, properly bled, is the way to go even though I know others here have gone a different route. The adjustable valve really shouldn't be needed unless you end up with a front/ rear bias issue. http://stoptech.com/technical-support/technical-white-papers/proportioning-valves
Bleeder screws must point upwards to remove all the air, you may have to remove the caliper and reposition on the rotor so the bleeders are pointing upwards. Once the system is bled, then you can remount the caliper back in its proper position. Even with those vacuum type brake bleeders, if the bleeder is pointing downwards, air will still be trapped at the top of the caliper. With my rear disc brakes, I have to remove the upper caliper mounting bolt, then tilt the caliper back so bleeder is more upwards. Most manufacturers who make upgrades to 4 wheel discs, recommend M/C bores of 1 to 1 1/8".......good luck!
