Cure for stripped thread that doesn't cost limbs
 

So I screwed up when changing tranny fluid by cross-threading the 10mm-1 bolt that goes into the torque converter (1999 ML320). Or I guess you could say 'screwed sideways'.

Anyway, I am contemplating what can be done to repair this. The bolt is in good shape, the threads on the inside of the TQ are blown and some of them even came out.

I would consider a tap and die but for the shavings that could end up inside. J-B Weld or Pro-Poxy 20 are other options that have been recommended.

This car has 105 k miles and I have recently brought it back to life by doing various service items. It was running really nice and I'd like to keep it for a while. Someone who has seen this or similar before please let your voice be heard.

If you are certain that the threaded section of the bolt is in fact 10 mm in diameter and the pitch is 1 mm you may be in luck. I'm going to assume that from your description you have not destroyed all the internal threading all the way through the material of the torque converter. Sounds like you started the bolt cross threaded and after tightening it some realized that and removed it destroying some of the threads at the entrance to the opening. If this appears to be the circumstance you find yourself in there is a fix with a tool that will cost you about $75!

The KD Tools Back-Tap expandable re-threader for internal threads is available from numerous online tool sources including SEARS.

http://www.sears.com/shc/s/p_10153_12605_00996251000P

You'll have to be thoughtful and careful but if you are, you might be able to clean the threads up enough to use a good bolt of original size (I would buy a new bolt)

Here's another tool designed to accomplish the same thing that is supposed to work 8-11 mm and cost $90, I've never used this tool and can't say whether it is made well enough or designed well enough to get the repair done.

I have used the KD type tool, and if you’re careful they work well. Good Luck!

Billybob, thanks for the lead, that looks very promising!

Being a relative noob to this type of work (but a fast learner, I hope), I have a followon question or two.

Yes the original bolt is 10mm-1. I verified this at two stores with their sizing templates.

The nut at this time is partly stripped out. Parts of coil (helicoil? I don't know) fell out during the initial extraction - looked like part of a coiled spring so this was clearly an insert of some kind.

I see the KD Tools "uses the good threads at the base of the port" per the description. I can't be sure there ARE any good threads, I can say there is some stuff left over inside. Is it possible it would work?

Also, given the original threads are probably an insert, isn't the original sleeve (prior to any insert) slightly larger than 10mm, as the insert would take up some size on its own?

Feel free to PM. I appreciate your posting this and hoping I can find a way out of this mess. I did use propoxy 20 per a prior recommendation and it ALMOST did the job, but a small leak has made itself evident. I may even re-patch it with the same material to create a 'dam' effect.

Edit: Looks like you forgot to paste the link for that other tool...

Doesn't sound so good if you got bits of old thread falling out - it sounds like you'd need to make the hole larger for a repair to work.

You mention that the old threads are probably an insert - that may be true but the screw hole could be made from a different metal such as an aluminum alloy. I DON'T KNOW THIS FOR SURE I'M GUESSING - as you often get that kind of effect from stripped threads in these light alloys.

A picture would probably help if you can take one. If not perhaps a parts diagram can confirm if the thread is indeed on a separate insert...

Thanks. The thread responds to a magnet so it is not aluminum. The torque converter is steel. Now I don't know if the intermediate material is something else...

I will post a pic of the removed thread later tonight. Suffice for now to say that it is 3-4 turns, looks very much like a spring (albeit a bit distorted).

Here are the pieces. The original bolt (in good shape), the part that fell out of the nut and is presumably a thread insert, and the original washer.

Update: since posting the original post above I have inserted a new bolt and secured it with a steel-based epoxy (Pro-Poxy 20). This came recommended by a mechanic. The first application produced a small leak (2-3 drops/day) so I have reinforced the seal with a little more material and it is now under observation.

Even if this holds I am concerned that the added weight of the epoxy, although it is only half an ounce or so, might affect the balance of the torque converter. In driving I cannot tell a difference. If someone can speak to this with good info/experience I'd appreciate it.

If it's driving OK and not leaking I would count my blessings and not worry about it.

Ah, but it IS leaking. Very slightly and drives ok.

I am looking into a Time-Sert solution. I will drill slowly by hand and use all possible precautions to prevent shavings. If anyone has thoughts on this please chime in. Thanks.

It will not be easy to stop swarf from getting into the torque converter - if for example you were trying to drill out a spark plug hole then you could apply a constant flow of pressurised air via the inlet manifold to help push any debris back out of the hole you're drilling. I don't see how you can do that with a torque converter - especially when it is in place.

Let us all know how you get on.

Closure
 

Well after over a week and about 200 miles of driving my ML with the repaired TQ drain plug hole, I think I can put this to bed.

What worked is the Time-Sert kit of tools. This consists of a drill, counterbore, tap, insertion tool and inserts of various sizes. I went with a 6.2mm depth and it seems to have worked fine.

The hardest part of this job was keeping shavings out of the whole thing. I used grease to capture them, turned the tools by hand, withdrawing and cleaning/regreasing them every half turn, repeating. I also used a small rare earth magnet at the end and captured a couple of very small shavings. I also squirted trans fluid into the TQ using an enema bottle (!) and let it drain out quickly, presumably draining small debris with it.

My thanks to those on this thread and in PMs who helped out with advice.

Congratulations - sounds like you did all you could - smart thinking with that unspeakable bottle! (A much kinder use for it)

Yes, I got to thinking with all the elements that made up this fiasco, a Freudian would have a great time with many parts of it. Maybe that's why I used the four-letter S word so many times during this ordeal.;)