I have a 68 S code, 4 speed XR-7 and changing the rear drums to disc. I’m keeping everything in case I decide to put drums back at some point.
The car has factory power front disc. My question is regarding the proportioning valve. Will the factory valve work with the rear disc or will I need to swap for an aftermarket valve?
Thanks
You should not need one. A proportioning valve is for disc / drum systems. You will need a proper master cylinder.
Royce is right, you will need to obtain the correct master cylinder - one that has enough capacity to provide the rear brake calipers with fluid. Your existing master cylinder does not have sufficient capacity.
In the 1970 B302 Chassis Modification Guide, a Ford truck master cylinder (with the check valves removed) was specified when 4-wheel disc brakes were added. We used a 1386 master cylinder on the 1970 B302 Trans/Am road racer we built. But this car did not have power brakes and this M/C won’t clear the shock tower with a power booster.
It’s been my experience that you will need to replace the factory proportioning valve with an adjustable valve. Since there are a wide variation of rear disc brake kits (with a wide variation of brake grip), you will need to adjust the proportioning valve such that the front brakes lock up first during a panic stop. This avoids having your Cougar swap ends during panic stops!
The Lincoln Versailles from 1977 - 1980 had four wheel disc brakes and used a Bendix brake booster. One of the master cylinders might work perfectly with a 4 wheel disc setup.
One thing you won’t have is better brakes.
I think you will find that all the Versailles/Granada/Monarch 4-wheel disc brake cars used the hydro-boost setup with a 45 deg canted M/C mounting pattern - not compatible with a Cougar brake booster.
Well that would be pretty weird! I don’t think I will be trying that in my lifetime.
Thanks guys, appreciate the advice.