I have a 78 Bronco custom, 400, C-6, 205, D-44 fr., 9" rr. stock discs on front, stock drums on back. Here is my problem: I have replaced the master cylinder, power booster, calipers, rotors, pads, drums, shoes, hardware, wheel cylinders, proportioning valve, and all lines. I have gravity bled, pedal bled, vavuum bled and pressure bled. I can't find any leeks or air. I bought an SSBC line pressure guage kit and am getting 1400# on front and 600# on rear.
With all this work I still can't get the front to lock up and the pedal still feels mushy. I almost forgot....I have also adjusted the plunger on the booster to factory spec. Then took it out to the point of pressure build-up (not releasing pressure) then backed it off a hair. The only difference I felt was the pedal started activating the system sooner, but no change in feel. The brakes work....but not near good enough to put it back on the road.
Any ideas would be appreciated! I've never had this problem with any other vehicle!
Since you seem to have replaced everything and have mushy brakes, the problem is almost 99% sure to be air in the system.
Here is the proper procedure for bleeding the system. If you didn't follow it, then you will still have air in the system.
1. Bench bleed the master cylinder. It requires plugs in the brake line connections and a little caution so you don't spray brake fluid all over the place. I use a rubber glove and hold it around the front reservoir to keep the fluid inside.
A. Mount the Master cylinder in a vise.
B. Fill the reservoirs to about a 1/2 inch from the top, one at a time.
C. Wait til some fluid starts to drip from brake line connection for the reservoir just filled, then install a plug, (I use the old connector with a small piece of the pipe flattened and folded over).
D. Repeat the process for the rear reservoir. This provides lub for the piston.
E. Using a blunt tool press the piston all the way in and hold for a couple of seconds. (This part takes a while, (if you press too fast you will spray fluid from the front reservoir).
F. Repeat this process until you can no longer get bubbles in the rear reservoir. (wait 5 to 15 seconds between each press on the piston so you don't aerate the fluid)
G. You should end up only being able to press the piston in about 1/8 of an inch.
H. Again make sure not even one bubble comes out when you press the piston or it is not properly bleed.
2. After installing the Master Cylinder on the booster and all the lines are hooked up to the brakes and proportioning valve, remove one plug at a time and hook the lines to the master cylinder.
3. Bleed the brake lines one at a time starting with the rear right, then rear left, front right and finally front left. (I use a one man bleeder bottle system to reduce the amount of fluid wasted, and also it will not draw air back into the system, only the fluid in the bottle. I find it still helps if someone presses the brake peddle while I watch to make sure that absolutely no more air is in that line. Even after it appears that there is no more air, I still go through a couple more presses to make sure. As the bottle fills I return it to the reservoir that is supplying the fluid, that is a personal choice since the fluid is new and clean, you may want to only fill it from the new can). If I were bleeding old lines that contain old fluid. I would not return it to the Master cylinder.
Good luck,
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