I was attempting to tighten the sway bar mounts to the frame (on my new addco 1 1/8") at the factory 15-20 pounds when the nut broke inside the frame. The bolt goes in fine but just spins. Thank god the car is undegoing a frame off restoration. I can get my arm and a wrench to the bolt/nut in question from the font of the frame. If I use a nylon inserted nut inside the frame, will this be ok?

I really don't see another viable alternative.

There is no "nut" in the frame. The metal is flanged inward forming what looks like a tube sticking up inside the frame. Before you put a nut inside, drill the hole larger until the "tube" is gone, then use a nut or see if you can find a "nutsert" it's a rivet that has threads inside. Another alternative is to drill out all the holes and make a threaded plate to fit inside the subframe, also look for an upward dent in the sub between the holes, mine has one, you may have to make a relief in the plate to miss this dent so it will sit flat. I'd drill a hole in the subframe half-way between the two holes, (middle of dent) and tack weld the plate in there so you won't have to fight it in the future if you remove the bar.

thanks david. I see what you are talking about with the "tube" I will try to drill it out and use a slightly larger nut/bolt combo.

They "punched and threaded" several things back then b/c it is cheap, imho..

pdq67

Just to let you guys know that the fix worked great. Now that I see how the bolt are held in I fell more confident about the bolt I put in (used a nylon inserted nut) than the other three.

Just out of interest Brad, what size bolts did you use to fasten the sway bar brackets to the chassis with?
My 1969 chassis manual (UPC3/A5) suggests GM#9431970 which is AMK Product's #B-10413 which are a 3/8" unc.
The "correct" sway bar bolts I recieved from amother supplier (Classic Muscle), were also 3/8" unc yet my originals are 5/16" unc and there is no way in hell I could fit these suposedly correct 3/8" bolts into the chassis' threads.. -so I black-oxided the originals and fitted them back in.

I have 3 subframes at my house at the moment ( :rolleyes: ) and they all will-not accept the "correct" 3/8" bolts. One is a 1967 and two are 1969s (or later Nova or..). The sway bar bracket I am using is the early production 1969 sway bar bracket with the "hump" bush, and not the later brackets with the bush retaining "fingers" on them.

I too had a stripped thread so I drilled it over-size, ground down the internal thread (that was the hard part), and welded in a 5/16" weld nut off an old bent up latch support. Lovely!

My originals were 5/16. The bolts I got from addco for the new sway bar were correct, but I thought the heads were a little small. So I actually used my originals in the new brackets. Except for the for the bolt that stripped, there I drilled it out and went with a 3/8 and nylon inserted nut.

The original bolts were 5/16 coarse, and that's what the threads on the subframe are. Also, this is a good place for good fasteners, that 1" bar puts a lot of stress on things. After "losing" a couple of the original fasteners, I picked up some 5/16 by 1 1/4" grade 8 bolts and hardened flat and lock washers, no more problems.