did a 68 charger for a guy. They put a kit on the front disc brake kit from I believe it was primoclassics on here I bet over 8+ years ago. It was suppose to be a factory replacement kit with everything from master cylinder to spindles and all other parts. It assembled good. He also wanted rear disc brakes on the car so we bought a kit from speedway motors that welded the caliper brackets on and mounted the brakes. A friend put them on his pro street dart and they worked out great. Well car has never had solid feeling brakes and now hes complaining that even with line lock on all it does is slides the front wheels. They don't hold and will slightly roll forward while applying the brakes and gas. Not solid enough. Any ideas? Car doesn't get driven a lot but he wants good brake naturally. Car is a 440 auto car. Could it be not enough vacuum? Or portioning valve issue? would an adjustable one work? If so who makes the best?