I have a 1968 Mustang with the drivetrain and braking system out of a 1970 cougar. The car has rear drum front disk power brakes. Ive already put a new Master cylinder, for the cougar setup, on the car. It was originally a 200 I6. My problem is the brake pedal had no resistance until you press it in 3 or 4 inches,at which point it rock hard. Within that 3 to 4 inches is your braking, which if way too touchy. I believe the front brakes are applying too much. It still has the original distribution block which is probably not a good idea. Would there be a way to correct this with an adjust proportioning valve if that were the case.

Thanks

 

I would try to find the proper proportioning valve, but an adjustable will help. There is a difference between non power and power brake pedals. Do you still have the non power pedal in the car? Is you brake pedal rod adjustable?

 

I believe the problem is that there is NO proportioning valve in the original distribution block, which may be compounded by misadjusted rear shoes. When you step on the pedal, you're putting all that pedal effort straight to the rear drums which require much less pressure to operate than the discs up front. As soon as the drums firm up, you start applying some pressure to the front which firms up the pedal.

You either need a combo metering/proportioning valve or an adjustable in-line proportioning valve. And I'd also go and check the adjustment on the rear shoes.