79-80's used a different thread. One is a 10mm x 1.5 mm, one is a 10mm x 1 mm. Cant remember which. 79-80 is th thread pitch that you can never find at parts supply places.

Drum brakes have a residual pressure valve usually. Leaves about 5psi in the line to keep the rear wheel cylinders from retracting away from the shoes. If you use this with a disc brake rear, the rear brakes will drag. It can also cause the rear brakes to lock before the front calipers even begin to move.

 

dyno, and swaping the master cylinder fixes this problem??

 

Master cylinder AND proportioning valve located next to the master cylinder (the thing most of the brake lines go to...)