I purchased and installed the front disk conversion kit from Ground Up in my 1968 chevelle SS. The car has a large block and also wide tires and mags (10n inches rear). The car's stopping power is poor; not as good as with the original drum brakes. It is not possible to lock the brakes above 15 mph. The pedal is firm to hard and will not reach the floor (guaranteed no air in the lines). I tried installing a larger booster (11") than came with the kit but that did not make much difference. The vacuum appears to be sufficient. Any thoughts?

Did you bench bleed the master cylinder?

Sounds like my car with 71 disc. front.Did the kit come with a proportion valvel?

ttt