When my rear chrome bumper was flattened against the body on the
passenger side, I used all the methods described by Chris Turner and Jim
Felder and one more ... I made a mound of fine sand to lay the face of
the bumper on when pounding from the inside.  That kept the face of the
bumper from having small new dents as a result of the procedure.

when I put the bumper back on, I had to add a single flat washer between
the bumper and the bracket on the passenger side so that the screw,
through the endcap, would line up with the hole in the quarter panel.

When I point the bumper out to folks they invariably say, "If you hadn't
told me I'd have never known".

Mike

Jim Felder wrote:
> I agree with Chris. When I got my bumper, it was badly mangled. Since
> then, it's been hit and bent but never so badly twisted. All three
> times, though (different kinds of dents from sharp creases to broad
> twists) I used a workmate, a three foot section of four by four, a
> sledge hammer, various pieces of two-by-fours, and--this is very
> important--a big crescent wrench.
>
> I have also used C-clamps (I have some really big one) to clamp a dent
> between two pieces of wood and apply great force.
>
> The crescent wrench (or big pair of pliers) can be used to at least
> head everything back in the right direction by setting the wrench to
> barely fit over the metal and gently bend the edges up or down every
> few inches. Don't try to do much at once.
>
> A whack with a block of wood to spread the hammer blow also works
> well. Get the top and bottom of the bumper surfaces as parallel as
> possible before going after any dents.
>
> If a part is dented in, turn the bumper fac down on a board and tap
> the dent out with the end of a two by four.
>
> If it's dented the other way, work from the outside.
>
> It takes a surprisingly short time to do this, maybe 15 to 20 minutes
> after all the tools and wood are gathered.
>
> Well worth the effort.
>
> Jim