markpaul

I have a '91 S4 that has a rear bumper that has been slightly pushed in in the middle. Looks like the car has backed into something and the bumper has not fully recovered to its original shape. I took it to a panelbeater to get a quote for some touch ups & he said he thinks perhaps it's missing some foam behind the rear bumper to keep it in shape that may have been removed when the bumper had been painted previously. Does the 928 S4 have anything of the sort behind the rear bumper?
Would like to know to avoid having to remove the bumper to find out. In any case I'll need to figure out how to get the bumper back into shape somehow. it's not bad and can't really be seen when you're close, but from a distance it's obvious.

Mrmerlin

it would help if you could post pictures of the rear of the car and take pictures of the inner bumper to chassis mounts,
this will determine if you have the collapsible cans or the impact shock mounts, and if they might be damaged.

NOTE the PU cover sits on the top edge of the inner bumper and if you have bumperettes then these will press the PU to the bumper.

If the bumper or its mounts have been damaged by pushing the car then the PU cover must first be removed,
and then its a good time to replace the bumper beading..
Otherwise there isnt any sort of foam pad thats installed,
if you do have the impact shocks then these are one time use ,
even though they could have been pulled out.
new used units could be used

Tim Noce

Following this closely. Look forward to any updates.

Bucko74

I picked up a second had rear bumper for my 84 and on first glance it appeared flawless, but then one day I noticed there was a sort of warped spot right in the middle that was supposed to be perfectly flat. DId some basic research and Polyurethane will hold shape in definitely as long as its not under pressure for a sustained period, and is not subjected to constant hot/cold cycles. My understanding (I'm not expert) is that you can reshape them so I laid mine flat on a bench upside down and stacked a heap of steel plate offcuts on the area that needed re-flattening. Left this for about 6months (didn't need the bumper straight away), and it seems like 95% of the imperfection is now gone. Not sure how you fix your problem without removing the bumber as Mr Merlin suggests.

A friend suggested some mild heat whilst trying to 'pull' on the problem area, but I cant see that doing much other than ruining the paintwork.