: 70 DeVille convertible master cylinder vacuum booster always activated

07-27-13, 08:27 AM
I installed a new master and vacuum booster on my 70 DeVille convertible one year ago. Recently I heard scraping noises and smelled hot metal so I checked all four wheels, and sure enough the front wheel hubs were red hot. So I jacked up the car and removed the front wheels. The pads were worn down to the nub and the rotors were badly grooved and the caliper pistons were fully extended. I assumed the calipers were bad and just stuck, so I proceeded with a complete front brake job. It needed it anyway. Someone in the past had replaced just one rotor and one caliper. After installing new bearings and seals, new rotors/hubs, new calipers, new pads, and new flexible brake lines to the calipers, and after bleeding the entire system, the front brake pads were constantly dragging on the rotors and I could not spin the wheels by hand. When I took it for a test drive around the block, the hubs and wheels became very hot just driving around the block. Only after jacking it up again and disconnecting the vacuum supply hose from the booster could I spin the wheels and tires by hand. And after test driving it without power assist it does release the caliper pressure on the pads and rotors and the wheels spin freely and don't get hot. It became apparent that the booster was constantly slightly activated. I've read in other GM car forums that it's possible the push rod from the brake pedal to the booster may be too long. But I can't find any adjustment for it. Does anyone know the solution?