TF rear crash cans.

  I've tried to remove the rear bumper on my car, but despite plenty of plus gas sprayed and left for days then wire brushing the exposed thread,
         the usual thing has happened the bolts turn but twist the arm.   Now I cant get anything in to cut through the bolts.  Any ideas/suggestions on how I might 
        overcome the problem would be welcome.    Many thanks.  Glyn. 

Can you photograph the problem? Can't tell how bad, bad is unless we can see it

You won’t be using those cans again, I wouldn’t have thought. The likelihood of shifting the rusted bolts hovers around nil, the only force you can apply is brute. In my experience it’s just a matter of screwing the bolt about until you tear the steel apart. The crash cans are not structural members in any formal sense of the word, they hold the bumper on & crumple when rear ended, supposedly to save the bumper. They are not heavy gauge steel & will work harden & fail with only a medium amount of perspiration & depending upon the time of day, a couple of cups of tea/glasses of beer 🍻, repeated half turns, interspersed with looking on eBay for replacement, will see success.
This is a rhetorical question:
Can you remove the cans from inside the boot space, with the bumper attached & work on it off the car? I still think it’s a brute force job but it can be done in the warm instead of it being a frozen finger fumbling job.
M

Hi and thanks for your interest/reply. Found an old reply to this problem, tried it and success the bumper is off.
8 nuts in the boot that hold the bolts holding the cans to the car, pull the top of the bumper out and down then you have enough access to the bolts to fit a spanner (10mm) then a 13mm socket on the nuts in the boot undo,
job done. Regards Glyn.

Yep, inside boot job. See my reply to Cobber.
Thanks Glyn.

Good stuff, did you manage to save the can?
M

I might be able to if I can get a cutting disc between the bolt and inside of the bumper.

Some laugh at me for having so many different grinders but I have 3", 4", 4.5", 5", some with low profile gearboxes, some short, some narrow and then things like Dremels die grinders etc. to get into awkward places, There is always a way to get that bastard bolt out.
Even if you cut through the damned can with a sabre saw, in oder to get better access to the bolt, and have to replace the can.

Hi I've tackled harder jobs than this on cars so I'm sure I'll get it fixed without cutting the can up.

Ive heard about these bumper to can bolts being a PITA to remove before. In fact Ive a set of reversing sensors Ive been meaning to fit but have left them on the shelf out of concern at getting stuck with a half on half of bumper.

Reading the work around here about would it be best to forget about the bumper to can bolts and just instead unbolt the assembly from inside the boot. Would the bumper then just lift away with it's cans attached.?

I would recommend removing the bumper via the boot but bare in mind that the bolts aren't captive.
Trying to undo the bolts from the underside of the bumper always end's in tears. 

Once you have the bumper off, assuming you have removed it via the boot, do all in your powers to free it from the crash cans.
Once free you can refit them to the car, in the correct place, delineated by the original fixing points & with a generous amount of copper slip (et al).
Needless to say when you are remounting the bumper, use copper slip again.
Equate the energies expended to the amount you apply, this sends a message to the car that buggering about doesn’t wash with you.
If you fit the reversing sensors consider fitting 3.5mm right angled jack plugs to their leads & 3.5mm sockets on the outer valance.
These expedients allow the rear bumper to be removed easily; unplugging the plug/socket system makes walking away with it in seconds as opposed to ages undoing wires from inside the boot & threading them in or out.
You can also dress the wires to the appropriate length.
M