Helicoil in Transmission

Went about trying to fix a leaking D18 adapter gasket tonight. It's leaked twice in the last year, this is the third time the case is coming down. So I start trying to do a better job at diagnosing the cause, and I find the same symptom as last time: loose hardware. It is the very bottom bolt, back side on the very bottom "ear" of the case. I tried tightening it, and it went in a little, then sort of felt like it was stripping. Pulled it out, threads looked good. Put a little bit longer bolt in, it bottomed out. Put a new bolt in same size as the original, it felt like it was stripping, but when I pulled it out I discovered why: Bits of helicoil in my adapter plate! I got the trans used out of a J-truck and rebuilt it. Not sure how I missed the helicoil, three times now actually, but I can definitely see where it's allowing the gasket to gap and leak 90wt. So, what to do about it?

At this point, think a new helicoil would allow enough torque to keep the D18 tight to the adapter?

Should I pull the whole case down, drill and tap a larger bolt?

 

if there is enough metal to tap i would go that route if not then try another helicoil

 

I would use perematex on the new helicoil, then on the bolt as well.

might even use 2 heli's to prevent stripping out.

 

If installed correctly, a heilcoil is better than the threads that were in the part originaly. However, put in half way and they are prone to problems.

See if you can pull the heilcoil out either by unwinding it or threading it out. Look at the threads and see if t hey are stright in the hole, if so, you can reinstall the heilcoil---besure to check depth that all of the heilcoil will be in the case, if not--drill further, but do not drill all the way through, you want the heilcoil to tighten up against the lip. If you can't drill further, cut a few coils off the heilcoil. You also want to be sure to remove the tang that allows you to screw the heilcoil in---this will prevent the bolt from threading all the way in. Once set up to install the heilcoil---use some sealer to seal the coils and some sealer on your bolt and you should never have a problem with it again.

One last throught----the striping feeling you felt when tighten up the bolt may have been the heilcoil threading deeper in the case---the reason you want to leave a "lip" for it to butt up against. If they have drill all the way through---lock it in place with Red Locite. Be sure to clean the threads of oil and you should not have a problem with it.

 

Well, it's running again. Crossing my fingers. Drilled/chased out the old helicoil, new one in with red LocTite, new grade 8 bolt with LocTite and lock washer. Filled it back up with 90wt. Saw one drop, but I'm pretty sure it just fell off the crossmember. Took it for a spin, gonna check again in the morning.

 

Went out this morning, still just the one drop from last night.
Drove it to work, didn't notice anything when I came out this afternoon.
Drove it home, I see one drop again, it's been sitting there a couple hours now. I'll call that "within limits." (We are talking about a D18 here, afterall. )

Thanks for the help, fellas.

 

Well, the helicoil lasted me up until a month ago; the dunes of Little Sahara did it in. Crossmember dropped out of the HEEP, trans and t-case were being held up by the rear driveshaft. It wasn't pretty. Anyway, the aftermath is that the t-case wanted to bend upward because of the d-shaft, and the trans wanted to go downward because of the motor mounts, and I think it worked the helicoil loose a little.

I'm thinking about trying that stud gimmick this time. What are the recommendations? There's not a whole lot of extra material on the ear of that t-case, and it's a soft iron, too.

 

I personally am not a big fan of helicoils. There are several other methods to repair a blind threaded hole.
1) weld it closed and then drill and tap a new hole
2) drill the hole oversize , tap it for a bigger thread , them stick in a larger bolt and cut it off. Next, drill out that bolt for your original thread. Make sure you set the bigger thread with a centerpunch to keep it in place.
3) MY favorite method... There are a number of companies that make threaded bushings. Some have locticte on them, some have locking pins. I like those style the best. Drill out the stripped hole for the thread on the insert od, and tap the hole. Apply
locticte or another high temp thread sealer. Threads typically have 75% engagement, so the sealer fills in the last 25% and makes the hole airtight.
Screw in your insert and tap down the locking pins. Your done, and it will last forever. I have repaired industrial machinery with this method fairly often. I have never seen an insert fail that was properly installed. I can't say the same about helicoils.

 

I've heard about these and am very interested. Do you have a brand name or brand line that I could Google?

 

Keenserts are indeed the brand I have always used, course I couldn't come up with the name until Patrick said it. Gettin' old, memory going. The picture on the website shows the tabs sticking up. Those get tapped down and wedge the insert.