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Old 09-19-2012, 12:01 AM
daflyinskwirl daflyinskwirl is offline
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Manual setup. Worked, now doesn't.

Hello all. I lurk here a lot, and have gathered a lot of great information but now I have a specific issue that I need help with.

I successfully modified a car with a manual brake setup.
Modified the brake pedal for a 6.28:1 pedal ratio.
Used a wilwood tandem master cylinder 7/8" bore.
Calipers were stock (front disc)
rear wheel cylinders were stock (rear drum)
I had a 10lbs residual pressure valve for the rear drums
I had a metering/ hold off valve for the front calipers
I had a proportioning valve for the rear
I made all the lines were 3/16" hard line with a few stainless steel braided sections.

the car stopped well enough for me to feel comfortable driving it. Manual feels different from power, but I could lock the wheels easily.

that car is now stripped, and I wanted to bring the manual setup on to my current car for the sake of simplicity.

same pedal ratio
same master cylinder
same front calipers
rear is disc
NO residual pressure valve for the rear
NO metering/ hold off valve for the fronts
I have a proportioning valve for the rear calipers
I made all the lines... again, 3/16" steel lines with a few braided sections.

I have bled the system a hundred times. I even pulled the MC and bench bled it and reinstalled in the car, and re-bled the car. Same crap.

The pedal feels a bit spongy at first as I take up system slack, then it gets firm and I can't push it anymore about 3" from the floor.

the car slows, but does not come to a screeching halt even at very low speeds when stomping as hard as I possibly can on the pedal.

the pedal does not sink when holding it
I've bled the system many many times. 2 man method. Bench bled MC. Vacuum pump method. 1 man method. There is no way air is in the lines.

I'm 99% sure I have no leaks (pedal does not sink when constant pressure is applied for long periods of time)

The MC is practically brand new. I've had it for a few years, but it has fewer than 100 miles on it.

I am completely stumped as to why I cannot get the setup working. I'm assuming it may be related to switching from a disc/drum car to a disc/disc car, but if anything, increasing cylinder bore size at the caliper should INCREASE brake torque and DECREASE pedal effort... which is the opposite of what I'm currently experiencing.

any help or insight will be greatly appreciated. I'm calling wilwood tomorrow for technical advice also.
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