Join Date: Jan 2018
Location: Coopersville, MI
Since it looks like you don't have a power brake booster you really have no connection between the engine and the brake system. No vacuum or anything like that. I would be interested to see if you could reproduce it at a stand still. How long into a drive does it get hard to push? I might try to sit and the car and pump the brakes on and off for a similar amount of time and see if it does it with the engine off and at a stand still. If it does then you have something plumbed wrong. If that doesn't work wait for a while then start the engine and let it sit and idle up to temp and sit there for a while to see if the brake problem develops. Might want to set up some box fans to help keep air moving through the radiator. If it happens in this scenario, since you have no hard connection to the motor, you have to look for proximity connections. If you don't get it in either of these conditions than probably a problem in one of the wheels where the wheel cylinders don't want to move as the brake pads get hot.
1963 Impala Convertible (Frame off resto-mod in progress)
1963 Impala 2 door hardtop (Pro Street build in progress)
1963 Impala 4 door hardtop (Parts car)