Threaded insert for LCA brace in the chassis question

[LooseRocks]

I’m in the process of disassembly.  I found that there were only 3 bolts installed for the brace for the front of the rear LCAs/diff support.  After removing the brace, I found the hole that was missing the bolt actually had one in it.  It was just missing the head. I drilled the bolt, heated it and was able to extract it.  Awesome!  Unfortunately, it seems the reason for it breaking off in the first place was it was badly galled or cross threaded.  It probably broke off being inserted and who ever was doing the work deemed three bolts good/safe enough.

 

 

 

Now I’m in the process of trying to figure out what to do to remedy this situation.  I could just re-chase it but the damage on the left over nub looks to me that the hole is damage well beyond using that as the solution. 

 

The other “easy” option is to put a key locking threaded insert into that hole.  The thin wall threaded insert requires an M14x1.5 hole (12.8 mm drill size, ~.5”).    My question is, is there enough meat in the chassis (likely a captive nut) in that location for a hole that size?

 

The “hard” solution would be to fill the hole with a weld, drill it and re-tap.  This is probably outside of my comfort zone. 

[grannyknot]

I guess I would start by trying to re tap the original threads and see how the bolt feels, you don't want it wobbly.  I'm pretty sure that captive nut does not have enough meat to handle a M14 but it may be just fine with a 7/16". I know, I hate that too when someone does that but it may be the easiest option rather than weld it up and drill and re tap.

[JMortensen]

I would cut that nut out of the frame rail, weld another 10x1.25 nut to a little piece of sheet, and weld it back in.

[LooseRocks]

I guess I'll try chasing it first.  If that fails I might just do an M12x1.25.  The drill hole for that is .425" so there should be enough meat there for that.

[grannyknot]

If you do end up cutting it out you can get access from above by slicing through the floor pan, you'll will also be able to see how much meat is on the captive nut.

 

[LooseRocks]

I spent a little bit of time looking to see if there was already information/image available for that area of the chassis.  So far no luck.  If the chase thing doesn't work out (which I don't think it will) I was going to go M12 but I think I'm just going to fill/drill/tap instead.

[LooseRocks]

If I re-tap it and it works I know it's just going to be loose/weak.  And it being one of two bolt that is responsible for holding the front of the rear LCA to the car I just didn't feel good about that.  After going back and forth in my head about a million times I decided to cut that nut out.  I went in from the top (thanks granny).  The captive nut measured out to about 20 mm (.78").  I could have put in a thin wall M10 (M14 hole)  insert but thin wall are not recommended for high strength application.  That and I would have been left with about 3/32 of steel after running a tap.  Not ideal.

 

After taking in some measurements from below and figuring out where the window for the nut should be I marked my opening and said my prayers.

 

 

Pretty much hit the opening dead on.

 

 

The captive nut is made of an extremely hard material.  It took couple hours of quality time with a demel to get it gone.  I probably could have just enlarged the hole in the captive nut and just welded the new nut to the top.  There was enough room.  Maybe should of thought of that before I started hacking away.  Probably better this way anyways.  If you're going to go nine yards might as well take that last step.