not sure...drums brakes or discs? if its a disc then you may have warped a rotor. same thing happened to my friend in his SVT. when the pads wear in one directon (forward mostly) then you wont notice the problem driving forward, except you will have to replace that pad more frequently (if it has warped for a long time) but when backing up, because the pad hasnt worn in that direction, it will immeadiatley take hold on the warped part of the rotor and it wont break loose until you pull forward. also rust on the disc can cause a lockup, happens on drums too, so if you have drums, i would pull it apart and check it out, clean it good (really good) and see if it does it again. PM me if you dont understatd what i am getting at.

josh

95 GL MTX Zetec, Carbon Fiber hood: *neoprene seat covers *new SVT rear bumper *Proud Owner of 1962 Chevy Corvette 427