Well i just finished a DEK swap on monday and I've notice my brakes are acting up. Under regular driving, it brakes normal. The brake pedal seems fine and I slow to a stop like normal but when i'm traveling at highway speeds or just getting off from WOT; I'm trying to slow down fast, the pedal feels extremely hard like when the car is shut off and you have no hydraulic pressure. Once I'm down to 40-45 mph the car slows down like normal. The moment I laid into the brakes it feels like I'm getting brake fade along with the hard pedal feel. I have no idea what is causing this, has anyone experienced this before?
BTW I have the z32 caliper/cobra rotor setup. I know my rotors are due up to be changed but the pads have some life left and the brakes havent acted up like this before. I also checked the vacuum connection to the brake booster, the resovior is full and I dont have a fluid leak. Any help would be great.

 

Make sure the check valve is in place so your brake booster holds vaccume.