Driveline vibration out of now where! Help!

Pull the brake drums too, blow out and clean up in there at the Brake Shoes. Could have a stuck open wheel cylinder causing the break to drag. Also want to clean up and put a little thin film of Anti-seize on the Brake Backing Plates where the shoes slide back and forth on, they rust right here too.

Want those brake shoes returning back to their "at rest" position where they are not dragging on the drums. The wheel cylinders rust internally being Brake Fluid draws moisture. Were you getting clean fluid out of the back brakes when you bled them after doing your disc brake upgrade?

If the rear brake fluid was quite dirty and not clear at the back, this could be a clue to faulty rear wheel cylinders.