The captive nut in one of my acad front bumper brackets has come loose, so i can't remove the bracket from the valance panel. Any suggestions? I don't have a welder, too tight access to get the grinder in and because its just spinning, drilling it seems out of the question.

Got 4 weeks to get this thing back on the road and MOT'd, so i'm apologising in advance for the 10 million questions over the intervening weeks...

I can't recall how the aca was bolted together, can't you grip it with a vice grip?
If you're lucky, you can unscrew it or it breaks off. Otherwise you could drill the head of the bolt.

Nah, the captive nut isn't of the welded variety, its one of the ones that has a rectangular 'brace' welded over it - completely inaccessible. Drilling just seems like a massive pain in the ass as the bolt will constantly spin.

Remove the bumper & valence as one piece, by taking out the 4 x M7 bolts which attach the assembly to the 'goalposts'.
That gives access to the back of the U shaped brackets, then try wedging a large screwdriver blade against the cage which holds the M9 threaded square nut.
Soaking the latter in penetrating fluid for a day before attacking it may help...

How about grinding the head off the bolt so the bumper assembly comes off, then removing the little bolt that holds the bumper to the bracket and have someone to weld a new nut to the bracket or buy another one.

Thanks for the reply, Ken. Do you mean "wedge a screwdriver" as in try to use a screwdriver to squash the cage enough to hold the nut again? From what i remember the cage covers all 4 sides of the captive nut...?

Can't you close the cage up by reshaping it round the nut with a long chisel/blunt big screwdriver? Lots of heat and a bit of penetrating fluid might help. Penetrating fluid is mostly useless but heat always works.

I did look at that, but it looked to me like the space was too tight to get a grinder on the bolt head.

To be honest, the whole valance is shagged. I'm tempted just to buy a new one and a new set of brackets. Oh, and a new bumper, set of goalposts, harley coil, new wings, bonnet, get the toe board patched, fix the leaking roof, replace the........

When you get it off and look at the back of the U brackets, you'll see that one edge of the sheet metal cage is about 3 or 4 mm clear of the bracket.
A chisel may be a better bet if you haven't got a brute of a screwdriver handy, but it's the same technique I've used in the past on those 'orrible M7 caged nuts at the front end of an original Citroen chassis.
Squash the cage until it grips the nut again...

Impatience won out and i hacksaw'd through the bolt.

On an entirely unrelated note, anyone selling a good set of dyane fron bumper brackets?