I was putting my hood back on and one of the threaded mounts inside the hood broke lose. Now the bolt just spins with nothing to grab onto. There does not seem to be any access to the cavity. Any ideas would be very helpful.
Thanks!!

 

Man... not sure what you'd do. My DRM hood came with one of the sides cutout for access to it. I filled it back in when doing the body work on the hood.

You may have to cut the back side for access, then have a body shop have at it.

 

I had the same thing happen. I drilled it took the mount out and replaced it. Then I filled it back in and painted it. It was a pain but I couldnt see any other way to do it.

 

I was thinking I could cut a 2" access hole, big enough to get a wrench in. And assuming there is a hex head nut inside that cavity, I could use the wrench inside and my socket outside to tighten her down... Am I being too optimistic? Is there a hex head nut somehow mounted inside that cavity that I am screwing the bold into? Can I cut the bolt and replace the inside mount (if not already a nut) with a simple nut and new bolt? ARGH... not what I was hoping for prior to a Friday evening cruise

 

More than likely, GM used a rivet nut to capture the fastener. It's usually referred to as a "rivnut", basically a threaded insert that is placed inside a blind hole, then a special tool (similar to that used in securing rivets) is used to compress the insert forming flanges on either side of the thin flat surface. They use the same type of inserts elsewhere on the chassis.
This site has an image of what you're probably dealing with...
http://www.emhart.com/products/pop/popnut.asp
Short of replacing the hood, your idea of relieving a hole and using a nut on the other side is probably the only option.
However, you make not be able to remove the damaged rivet nut to replace it with a hex head nut.
What's probably occurred is that someone has tightened it down to much and the flanges have worn away on the underside of the fiberglass pocket. That's why the insert is just spinning now.
Drilling it out is a possibility, but it's steel and will more than likely just spin, enlarging the hole and/or damaging the fiberglass even further.
IF, you can access the inside of the hood area via an access hole, you might get lucky and be able to grasp the insert with a small set of needle nose VICEGRIPS.
Then you might be able to thread in the metric bolt and tighten if, further compressing the flanges on either side of the fiberglass. It takes some effort to do that. If you can secure it from spinning, then maybe drilling the top flange is possible...then use the fastener/nut arrangement. You'll need fender washers on the both sides if that's successful.
It's definitely a long shot and that fastener will always be a weak point...

 

Pics please

 

It the RivNut is spinning in the hood could you epoxy it so it wouldn't spin anymore?

 

Doubtful that any epoxy would hold it to withstand even minimal torque, but it might be worthwhile with nothing to lose. If the surface was metal, one could do a spot weld.

 

I appreciate the time, ideas and ugly thoughts I have gotten from everyone... so, I cut a small hole in the underside of the hood mount into the fiberglass with a hole saw. It is not what we thought. There is actually a metal reinforcement bar in the cavity, and it looks like a 4-sided nut that has broken lose. I think I can get it off now. However, if I replace it with a standard hex-nut & bolt, and tighten it down, will it hold? Maybe a tooth washer to help grab?? Epoxy or other adhesive? Or just a good grunt on the torque? Not sure if you can tell from the pics...


... a little closer

 

I'd use a split lock washer and/or some blue LOCTITE once you're able to get the damaged nut free. Don't over torque it.
I tried to find the torque specs but the source I checked didn't have the torque value. Someone might chime in. Just snug it up until you determine the correct specs.
"Toothed" washers are more for electrical ground connections. If you can get a flat washer under the new nut/split lock washer, it would be extra support, but maybe not needed since the metal structure is there.
They must mold that metal structure in there for just this reason. Maybe the spot weld on the oem nut broke loose? When I suggested the "rivnut", I didn't even consider a metal subframe in there.
Maybe you can find a plug of some type to fill in the hole?

 

Yep it is mounted on a plate both nuts are on the same plate. You will have to drill the rivits out to get it out or you could just tape a new nut on a long box end wrench and put it on that way. Get a pick up magnet to get the old nut out so it dont rattle around. Get a black hole plug from the hardware store to cover the hole and be done with it.

 

JW & Alan and others, THANKS for your input. I was able to remove the old bolt and retainer (it is not a nut, so I hesitate to call it that). Since it is the bottom bolt, I was able to cut the hole it what I hope is a inconspicuous area, but a black plug would look better. I am stuck now until I get to the hardware store tomorrow for new parts. Until then... I just keep kicking myself. When it is done, I will show pics of what all the fuss and work was about. Thanks again for everyone's help.

 

^ Nice work... a black plug would work well. That said, patching/painting that area wouldn't be too hard.

 

Cobra... I just had a custom piant job under the hood, so I was careful about the placement of the hole and hesitant to try to paint around it. That is why I had the damn thing off... and hope that it will be worth it.