I had to replace a couple of captured nuts on my fame for the transmission crossmember. I showed this in my build thread, but it's been many pages ago! I thought I would do a thread in case anyone was interested. This process works very well and eliminates the need to cut a hole in your frame. It's easy and you don't need a lot of experience to be successful. In this demo I was on my creeper looking up. The hardest part for me was overhead welding! Just take your time, be GENTLE, and it will come out great.
I hope this is useful to somebody.
These two nuts are stripped. I stripped them out while torquing them after reinstalling my crossmember. Glad it happened now! These are the two closest to the front spring hanger at the rearend.
Grind off the old paint.
I'm using the stripped factory nut to hold this bolt with the new nut in place.
Using a Sharpie, mark the lobes of the new nut.
Remove the bolt and nut... this is what you have.
I had to sharpen my chisel! Notch the hole at each lobe. The factory nuts broke out while notching.
After notching the lobes.
I tried to use my air chisel, but it didn't work for me. If you try this, go slow! Don't cut TOO much.
Hold the new nut in place. The bolt is nothing more than a handle at this point.
Using my shop hammer (3#) I carefully beat the nut into the notched hole. You can sort of "feel " the nut as it countersinks. Be careful NOT to knock the nut into the frame. If you do that, unscrew the bolt and get another nut!
The new nut is countersunk to the desired depth.
Leave the bolt in place while welding to protect the nut threads. You will probably have to clean the threads with a tap when you finish.
Welded and ground down.
Painted and done. When paint dries I can bolt my crossmember back up. The whole thing took me about an hour and a half.
I hope this is helpful to somebody! Good luck. PM me if you have questions.