You ever worked on something so long that you wished you never started. Well, I have, and this is what I did. Put disc brakes on the rear of my truck, thinking to improve stopping power. I've change boosters twice and master cylinder 3 times and still have no pedal at all. I brough a rear disc brake kit for 9" Ford rear, installed it with the 2 pound check valve and 1-1/8 master cylinder, pedal went to the floor, then tried the 1" MC. Even installed the Currie adjustable valve. Took to a local mechanic and he got a little braking out of it. drove it all 2023. At Carlisle in the fall I went back to the vendor whom I purchased the kit to pick his brains, well he said try a 3/4 MC, which I just did and no pedal. Right now, I have that MC on with 2 lb. in line front and back with the Currie valve. Bleed the brakes, get all the air out still no good. I do have disc brakes up front. The proportion valve has always been in the system. I sold my old brake drum set a year ago and it looks like I maybe looking to purchase new ones. Any help. Thanks
Clamp off the Brake hose to the rear brakes with a brake hose clamp. See if you have a good pedal now. If you do, take the residual valve out and throw it as far as you can, it's not working. Likely a Wilwood valve. Then replace it with a good valve, not Wilwood.
You're going the wrong direction with your M/C bore sizes, you need more volume going to the calipers not less. You are increasing the force yes but also increasing the pedal travel needed to get the caliper piston to move
It's hard to sort things out without decent well lit photos to study. Other than that it often comes down to the thing of What isn't right withis picture? Over the past 62 years that i have been working on cars and trucks with at least some training some of the things i have seen with btakes are: 1. The guy bleeding the brakes had no ****ing clue about bleeding any brakes correctly. That includes a lot of Hamb members who hop in and offer totally wrong suggestions. The correct way if you are doing the pump it and hold it method is to have your helper pump the pedal SLOWLY and then hold the pedal down until you tell them to take their foot off the pedal or tell them to pump it SLOWLY again. No matter what you do it is near impossible to pump bleed the system by your self. I've tried most of the suggestions that the hacks toss out over the yeaes and most don't work well enough to get a good solid pedal. Using a pressure bleeder works great most of the time. Using a handhele vacuum pump works reasonably and the red metal one from HF has worked better than the plastic ones outside of the original Mighty Vac. 2. on rear disk brakes, having the calipers mounted wrong. Refer to one Trick pony's diagrams in post 4. one even told me he swapped calipers side to side so the bleeders would point down so he didn't get brake fluid on his freshly painted calipers. 3. mish match of parts that just don't work together. One was that the pushrod on the master cylinder ran out of travel before the pedal hit the floor. That one worked when you pressure bled the brakes until the brakes wore enough so that you ran out of travel before having full pressure on the brakes. That one came down to being that the guy who set up the brakes moved the point that the pin for the pushrod was too close to the pivot point to have full travel to bottoming out in the master cylinder. 4 . Push rod adjusted too tight and not leaving any free travel in the push rod plus having the port in the master cylinder covered or mostly covered by the piston not allowing the chamber in the bore fill quickly.
One thing I don't see mentioned is what kind of rear calipers you have. If they're the type that has the park brake built-in, they should have a lever sticking out of the caliper centered in the piston bore. IIRC, some (or most) of these need the park brake lever 'ratcheted' to remove excess free play for proper brake operation. Using the park brake often helps keep them adjusted.
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