Had Brakes, Now I Don't.
Okay, here's the story, short version. Car has been on the road for 9 years with great brakes. Wilwood 2 piston calipers on front, intermediate GM calipers on the rear, 1 1/8" bore master cylinder, 7" booster. This past winter I replaced the independents suspension rear end with a solid axle, OC. I replaced the GM calipers with Wilwood 4 piston calipers and matching solid rotors. When everything was complete, all air confirmed bled from system, I had very poor brakes. Solid pedal but the car just wouldn't stop. Wilwood rep told me to replace the master cylinder with a 1" or 7/8" bore. I did. I bought a $200.00 7/8" unit from Wilwood, bench bled it as per their instructions, bled the system, front and rear, and...same thing, no brakes.
I have 900 psi at the calipers, up from 500 with the 1 1/8" MC, but the car doesn't stop any better than it did with the larger bore MC. Now Wilwood tells me their 7/8" MC is not designed for power boosted brakes. I replaced their high dollar MC with a cheapy 1" from Car Quest...no brakes.
I have 800 psi at all calipers, 20 inches of vacuum at the booster and I've confirmed that the booster diaphragm is not leaking. The pedal seems solid with the engine off but when I add the manifold pressure the pedal is soft and goes nearly to the floor...and not enough brake to stop the car even at very low speeds, (10, 15, 20 mph)
What am I missing? The car is a 30 2door, steel,fenderless sedan. Total car weight is about 2800 lbs. It always stopped good, great even with the original GM calipers but they won't lend themselves to installation on the rear end I'm using now. They were originally mounted inboard, on sliders.