Most pulsating brakes are the front. They feel like they are the rear
brakes. Most times it is warped rotors. My brakes pulsated and they were the
back brakes. The Vanagon was up on blocks and the block crushed.The Vanagon
fell on the asphalt. Either the rear bearings bent, bearing housing, brake
drum,or stub axel. How to tell which? Replace them all with a new used hub.

Warped brake drum will do it. First,loosen the lug nuts and retighten them
correctly. Do the front rotors ,too. Did you do any recent maintiance or
repairs?