if i let go of the throttle and then push down i get knocking/bang from rear

[6pot]

I think from what your discribing it is the same as on mine! A slight knock when coming off the throttle, it is more prominant in "S" mode. Ive changed the rear box rubbers and all the prop shaft donuts are in good condtion, i thought it might be the axle mounts too but i have been too busy to look! i will be following this thread from now on!

 

[kth286]

worn (loose) subframe mounts come with some definate movement at the rear of the car when changing direction sharply.

Test as follows:

1. jack car body rear up using the normal wheel change jack, so that rear wheel is off floor. The subframe will now be hanging.

2. get second jack (trolley or bottle) and jack under the subframe (near front bush). You will see the subframe rise significantly when bushes worn.

Test other side the same.

It is the front ones that are the main problem first.

It is also a big rust spot (for the body) on some cars where the cavity bungs have not been sealed properly and moisture/water/muck/salt allowed in.

Be prepared - welding of body may be required.

 

[Sorry Pete]

Check this PDF of a DIY rear subframe mount replacement on a W201. Should be similar on a W124 unless the estate varies significantly.
Very detailed and lots of pics.

W201 subframe replacement