<e30> vibrating/thud when braking at low speeds in reverse

[Thomas.Wellington@xxxxxxxxx]

I am having the following problem which is getting increasingly worse.  

When I am backing the car up or simply rolling backwards and I apply the
brakes, there is a loud thud/vibration in the rear as soon as I hit the
brake pedal.  The noise appears to come from the rear wheels/ brakes
(could be the diff.?).  My brother seems to think it is the brakes
grabbing/locking.  Any ideas??

Thanks in advance.

Tom
1983 <e30> 323i Baur Cabriolet

------------------------------