what is this thing?

[85blackC-10]

When I got my truck this bolt had a piece of wood wedged between the washer and the frame. I got the piece of wood out cause it didn't seem quite right, but now the bolt won't tighten. And I have no idea what it goes to. any help?

EDIT: Location wise, it is on the passenger side right below where the back of the cab ends.

[zieg85]

Rear cab mount, should be a rubber piece between

[85blackC-10]

yeah the rubber piece is there, but the bolt just wants to turn and it won't tighten at all

[zieg85]

The nut is spinning then.  Never had to fix one so we'll sit back and see who responds.  Every cab I ever changed all 2 of them the bolts loosened up as they were supposed to.

[gildardo01]

the nut is in the cab under the carpet in most cases... its a square nut not a hex... you would want to loosen the bolt make sure its in good condition and not seized the bolt it back up and weld the square nut to the cab and your on your way... 

[Blazin]

You will need to use a hole saw and cut a hole in the floor sheet metal above the mount. Then you can get a hold of the nut to remove the bolt. Or weld the nut down and remove the bolt. Once you have it out clean up the threads, never sieze them, and re install the bolt.

[Cabcorner]

              The way I've done it is to cut the head off the bolt, then drive what's left of the bolt and the cage nut up through an access hole that I cut in the floor . I like to use a 4" grinder with a cut off wheel to cut the floor . If you measure carefully you can cut above the flanges on the rear cab support so that you'll have something to weld the access cover to if you choose to close it back up. I reuse the nut buy heating it until glows cherry red with a torch and then spin out what's left of the bolt . Sometimes you can drop the nut back in place and then pry the cage back around to hold it in place ,other times you have to tack it with weld or braze . That rear cab support doesn't look right to me for a 85, is it possible that the frame  is from an earlier truck?

[85blackC-10]

Well, sounds like that will be fun to fix. And cabcorner, if the PO swapped the frame, he failed to mention that when he sold it to me. But im 95% sure that its the original frame.

[Blazin]

When you weld the nut in place after your make the access hole the heat from that will be enough to let the bolt spin out of the nut. Once its welded you don't ever have to worry about it happening again.
I use a hole saw because it looks much nicer when your done. I also make a cover and rivit back in place so if for some reason you want to take the bolt out again you can give it a shot of weasel pee before hand.