Braking problems

I've been having problems with my brakes over the past few months after being given a '92 Grand Am with 108000 on it. On wet/damp days and also on the first few times that I hit the brakes, the rear brakes lock up immediately (before the front). Usually this only happens when I first start up the car, but last night while driving home in the snow, they locked up again when I just tapped on the pedal to slow down. Needless to say, at 50mph and a light coating of snow on the highway, I had to pull to the shoulder to avoid spinning out of control.

A mechanic told me that I should just cut the drums which to me wont fix the problem since the brakes will just readjust to the drums. I've changed the front rotors and pads, bled the system and the back brakes were just redone in July.

Any suggestions on what I can do to correct this issue?

Thanks

Jim

There are two things that I know of that would cause this:

1. Brake shoes installed incorrectly - If one shoe is thicker than the other, then the thicker one is the leading shoe.

2. Contaminated pads, usually from brake fluid leaks,
if this is the case the pads (as new as they are) are garbage - the fluid soaks in like a sponge.

i had the same problem i replaced the shoes, springs and the wheel cylinders. and it worked