I was working on replacing the trailing arm bushing on my 93 Civic Si Hatch yesterday, but while removing the bushing bolts, one got stuck on the way out. (The ones that go VERTICALLY into the frame.) Then it wouldn't go BACK IN, either, which is pretty weird. Put lots of Kroil penetrant on it but still wouldn't budge. Eventually the weld nut gave way on the underside while trying to put it back in with the impact driver, but not before it also broke the detente pin on the impact's anvil. Overall, not a great day.

COLES NOTES: See title of post.

It's not the end of the world, but it's damn annoying. I also want to repair it well while effecting the least amount of structural integrity loss to the vehicle. I'd like your advice/feedback on the following - or if you have new suggestions then I'm all ears. Based on my research, here are some options:

1. Rivnut / Rivet Nut / Blind Rivet
   • Pros: No need to drill hole in frame or access hole from inside the cabin.
   • Cons: Unsure if they make one in M12-1.25 - Acklands Grainger doesn't list them; it is strong enough?; bushing won't be flush with frame;
2. Cut access hole (hole saw or die grinder) in side of frame, install 2x nuts to lock bolt in place
   • Pros: Not a giant hole in cabin floor; not necessary to seal up when done; double locking nuts are strong
   • Cons: Affects structural integrity?; awkward side access vs. top-down
3. Cut access hole (hole saw or die grinder) in cabin floor, install 2x nuts to lock bolt in place
   • Pros: Easier top-down access; less integrity loss than a side hole; double locking nuts are strong
   • Cons: Risk of not aiming access hole in proper location; hole in cabin I would want to close up, but not permanently - not sure how to do this; hole in floor would be constant reminder of my idiocy

As always, thanks for the help, HT.

 

Rivnut is totally out, you'll see why in a minute. I think the other two ideas are somewhat out as well. What I think you'll need to do it cut out a section of sheetmetal underneath and weld a new nut in place.

Here's a picture of my '94 sedan (I never broke the welded nut believe it or not, even with all that rust you see) you'll notice that the metal on the bottom isn't really structural, it is (in my case was) just sheetmetal, the nut is welded to a tube that's welded to a bracket.

 

Rivnut is definitely out. But, that pic at least shows me that the sheet metal surrounding the mounting point is not the main structural. The main support likely comes from that bracket that's welded to the frame rail.

Ironic thing is the vehicle isn't really that rusty. I'm tempted to believe there was some other issue contributing to the problem of why I couldn't get the bolt out ... we shall see I guess.

Great pic, btw.

 

Normally the end of the bolt gets rusty, as it goes through the welded nut it gets hot, and can get to a point where it literally welds itself to the nut. Ideally spray lots of penetrating oil up through those holes beside the bolt first and use a really strong impact gun in the hopes the bolts will come out without having to put them in and out to try to break up the rust.