replaced the front pads and the back are drums, not pads.....


Ah! That opens up a new realm of possibilities.

Two things in particular to look for on your rear brakes:

Check for leaking wheel cylinders. If your rear brake shoes are saturated with brake fluid, this can cause the rear brakes to grab when applied.

Second, check that your rear brake mounting plate is properly secured to the rear axle. If the bolts that hold that plate in place (the plate is what your wheel cylinders and brake shoes are mounted on) are not tight, then when you apply the brakes the friction of the brake shoes on the brake drum will cause that plate to rotate slightly, and depending on the geometry of the attachment bolts can cause extreme brake grabbiness -- to the point of locking the rear wheels with the slightest application of the brakes.

tanstaafl.