We ran into a major snag while wrenching on the car today, and I’d like to see if anyone here has ever run into something similar, and if so, I'm curious about how you addressed the problem.

At some point during my car’s life (’83 944), someone has done some combination of cross-threading/stripping/over-torquing/clumsily re-drilling and tapping the outboard hole that holds the casterblock and rear part of the driver’s-side front control arm to the car. (Actually, they also managed to munge up the inboard hole on this side, too, but that has turned out to be much easier to fix than the outboard hole.)

This particular hole is a threaded hole in the body of the car, in a fully closed-off section of the chassis (i.e. there’s no way to just drill out the top of the section and put a nut on the end of the bolt as it comes through). Cleaning out the thread did not provide enough bite for the bolt to take any torque (the bolt just spins and spins once the head has contacted the bottom of the control arm.)

The current, best option to fix this problem is to drill out the hole, and re-tap it to accept an M12 * 1.5 bolt (the original hole as delivered from the factory was for an M10 bolt, so this basically makes it one size bigger.)

If the drill/re-tap solution doesn’t work, then much more drastic measures will need to be taken to essentially fabricate a new mount for this. This would be specialized enough work that the timing of having this done will put the Miller race in jeopardy, which is not something that I really want to think about at this point.

So, I’m curious if anyone has ever dealt with a stripped-out threaded hole in a chassis (whether this specific hole on the 944, or any similar hole on any other car). If so, how did you fix the problem, and how well did your fix hold up? The process of drilling and tapping a larger hole is destructive enough that I’d like to find out if there are other less-destructive options that have worked for those in a similar situation in the past.

Thanks for any help - I always knew something like this would occur during the build…I just hoped it wouldn’t happen so soon before the biggest race of the year, on such a critical component of the car!

Gary, it's your lucky day... I had the same problem on the same hole, and a M10x1.5 Helicoil insert solved it pretty easily. You're welcome to borrow my Helicoil kit... I'll be out of town for a few days, but I'll be at Chuck's house Tuesday night, as well as this coming weekend. All you have to do is drill it out with a 13/32 bit, run the special tap through it to create new threads for the insert, then screw the Helicoil insert in with their tool, and then you have fresh new threads for the original bolt (although you'll probably want to use a fresh bolt as well).

That bolt was cross-threaded when I bought the car, so it never could take much torque. I had it so that it worked well enough for a while, but after my crash at Gateway, I found that bolt was about 1/4 to 1/2 inch un-threaded. I'd imagine that was probably part of my problem, even though I now know that the cracked rear trailing arm was the main cause of the oversteer and inconsistency I was experiencing. Anyway, after the Gateway incident, it was totally done... no hope of even half-assing it back together one more time. I had never used a Helicoil before, so I didn't have much expectation of it working, but it really surprised me and seems to be a decent solution.

Thanks Weston!!! Sorry to hear that I’m not the only one who has experienced this unfortunate failure, but I appreciate your offer to let me use your Helicoil kit. If you don’t mind (and if you were already planning on going to Chuck’s anyway), could you plan to bring your kit over there? I’m not sure what my schedule is going to end up looking like this week, so I’m not sure if/when I’ll be able to make it over to Chuck’s to pick that up, but it will be extremely helpful if you’re able to bring that over there (or I can come by your place to pick it up later today, if that’s easier for you).

Given my schedule this week, and the close timing to the Miller race, I might also see if I can find a reasonably-priced kit on my side of town (Golden) since I’m sure this isn’t the last time that this problem will come up, but it definitely gives me some options if you’re willing to let me borrow your kit (working out the timing is the only real issue with that).

So, for now, could you plan to bring your kit to Chuck’s on Tuesday, or let me know if it would be easier for you if I swung by your house to pick it up? Also - what time of day were you planning on being at Chuck’s on Tuesday?

Thanks again!

Yup, I'll bring it over to Chuck's Tuesday night... I think he said he'd get home around 6:15pm, so that's the time I'm shooting for (assuming traffic cooperates). I'll just leave it in the back of my race car if I don't see you that night...

After much research today into the process of preparing and inserting a Helicoil piece into the car, we realized that both the hole that must be drilled, and the thread that must be cut, for the M10 * 1.5 Helicoil are VERY close to the same dimensions as the hole and tap required for an M12 * 1.5 bolt. So, we decided to go ahead and drill/tap a hole for this (since I already had the proper size drill and tap) in preparation for borrowing Weston’s Helicoil kit, and then just try an M12 bolt in there to see if it would work, planning to go ahead with the Helicoil option later in the week if the M12 bolt wouldn’t quite work. Well, as luck would have it, the M12 * 1.5 bolt fit into the newly-cut threads perfectly, and was able to easily hold the right amount of torque!

Weston – So after all of that, I won’t need to borrow your Helicoil kit to fix this, though I really really appreciate you offering it, as the prep work on the hole for using one of those Helicoil inserts ended up providing the exact fix to the problem. Thanks also to Rick for actually performing the mind-numbingly-precise work of laying under the car to both drill out the hole, and to re-tap the threads at the proper angle!

And, thanks to everyone else who weighed in with a suggestion to this potentially race-weekend-threatening problem – it’s nice to have this problem behind us, and be back on track for the Utah weekend.

Glad to hear that you've got the problem solved!