How would you deal with this? (hidden fastener)
 

I'm getting ready to swap exhaust, clutch, etc. The P.O. tack welded the sub-frame brace parts together. No big deal, just remove the whole thing, right?

Well, one of the bolts (furthest forward, driver side) starts to loosen, then starts spinning. Seems I've broken the welded nut lose from the chassis. This nut does not appear to be accessible from inside the car. There's some sort of double thickness sheet metal at that point. Either that, or I'm blind.

I can neither remove nor tighten this bolt. Left as is, it will rattle (completely unacceptable). And, of course, it does nothing to hold the sub-frame bracing if not tightened down. I could hacksaw it off, but that leaves no way to install another bolt in it's place.

So, what would you do in this case? Drill a hole inside the car to get to the nut with vise grips? Something else? What would a dealer do besides leave it and hope the customer never noticed?

For reference, it's a 1994 base model. Suggestions appreciated.

To start with, have you used a rattle gun on it?

No. It spins freely by hand, no resistance. Tried pulling down on the brace to try to have friction help, to no avail.

Nothing? I'm the only one to ever have to deal with this?

Can the tack-welds be cut easily?

Which subframe brace? The factory one? Front, rear? Or is this an FM-style frame rail/butterfly?

--Ian

There is only one answer to this question , :fael:

In retrospect, yes. It would have been much simpler.

However, I now have the half lose bolt to deal with.

Factory. Tubes with the ends flattened. The front most bolt on drivers side is the issue. Welded in nut broke lose and spins freely, but I can't get the bolt out.

This is the rear one? The one that's shaped like a U with 6 bolts and one crosspiece at the back? (or more crosspieces on the 01+, I think). This one?

https://www.miataturbo.net/attachmen...ine=1460424126

Or is it the front one that's one tube with 2 bolts at each end:

https://www.miataturbo.net/attachmen...ine=1460424126

Assuming the bolt is just to hold the brace on (and not holding the front subframe to the unibody), then you probably don't need that attachment point (or at least, can do without it if you install something like the FM frame rails). In that case, what I'd do is use a cutoff wheel to remove the head from the bolt, remove the subframe brace, and then try to tack-weld the nut with the shank of the bolt inside it to the unibody so that it doesn't rattle around. After that I would reinstall the brace minus that attachment point.

The right fix probably involves cutting a piece of sheet metal out of the unibody, making a patch with a hole and a new welded nut, then welding the patch back to the car.

--Ian

Prybar and impact. Use the prybar to pull on the bolt head which will push the nut against the metal. Then hit it with the impact.

Yes.

I'd either have to cut the brace to avoid it banging against the bottom of the car, or find a way to fasten it down. Unfortunately for me, I think the patch method is probably best. Thanks.

never mind