Expert: Van - 11/6/2005

Question
1992 Chevy 454 ss pick up. Truck has been fitted with a 502 ci engine also equipped with a whipple supercharger. The front brakes get extremly hot after driving only a couple miles. Calipers and pads work fine. Brakes release as intended upon inspection. Question... Could the vacume booster somehow be causing the brakes to apply when driving?  

Answer
Hello David,
The vacuum booster could cause application of the brakes if there was a problem in it. The only problem I can think of that would cause it would be a plugged release vent, causing vacuum to be maintained against the diaphragm even after release of the pedal. Far fetched, but I guess possible.
The brake pedal rod not properly adjusted could also cause a not-quite-released condition, barely applying some brakes, or holding them applied.
One way to test it would be to disconnect the vacuum line from the engine, and plug it, and go for a ride. Of course be careful where and how you drive, because the remaining non assisted braking will be poor, but you will have brakes. See if they get hot then.

What I would more suspect is the front flex hoses from the frame to the backing plate. I have seen them become clogged at the metal clip mid-hose, where it bolts to the control arm. The hose deteriorates inside, and the rubber folds over, allowing the applied pressure to get by, but then acting as a check valve, and holding pressure on the pistons.

I have also seen pistons stick in calipers after the pressure was released. Air in the system can also act as a little spring, applying a slight amount of brake.
Water in the brake fluid can evaporate when heated by the brakes, and turn to steam, doing the same thing.

Van