Here’s an easy fix for captive nuts that have fallen off where you can’t get access to the back of the panel – steel blind rivet nuts.
No need for access at the back of the panel. I used these to repair the tailgate ball pin mount on an Audi A4 1.9 tdi Quattro. 10 off M8XL rivets cost me £2.79 inc delivery. Available in at least M4 to M12 for sheet metal 0.5mm to 8mm depending on diameter and supplier. There are various suppliers on eBay selling steel, stainless steel and aluminium blind rivet nuts.
You don’t need a £50 plus setting tool, you can set the rivet properly with a bolt, washer, nut and some copper slip/grease.
Select a bolt that will carry the nut, washer and rivet with a thread or 2 to spare. You need to grease the bolt threads at the head of the bolt where the nut will sit – this makes it a whole lot easier to set the rivet. Run the nut up to the head of the bolt and work it back and forwards a few threads to spread the grease.
Smear a small amount of grease on both sides of the washer, keeping it away from the hole. Slide the washer up the bolt making sure you don’t get any grease on the bolt threads.
Now run the rivet onto the bolt.
Its critical you don’t get grease on the bolt threads where the rivet threads sit, if you do, the rivet will most likely run off the bolt when you try to set it. You are relying on friction to stop the rivet unthreading as you turn the nut, hence the grease on the washer which lets the nut/washer rotate against the rivet face.
Drill out the hole to the given size for you rivet. Don’t let the drill shoot through as there may be cables present.
Insert the rivet/bolt assembly. Hold the bolt stationary and thread the nut towards the rivet to set it. Initially, it will take a bit of effort to deform the rivet. Once the rivet has set, back the nut off and unscrew the bolt from the rivet.