Stripped transfer case threads - repairable?

So today, I messed up. I didnt realize just how weak the aluminum of the transfer case is, and while changing the oil in the t-case i over-torqued the steel drain and fill plug bolts and stripped the inlet threading out of my aluminum transfer case.

i see there being a few options here.. would like to hear what you guys think/ reccomend.

1) find a junkyard, get a replacement transfer case, swap it out (time consuming, most expensive option and leaves me without a truck for a longer period of time)

2) tap new threading in the next bolt size up (would be going from 18x1.5 to 20x1.5). cheap and potentially effective. concerned with potentially leaving aluminum burrs / shavings in the case

3) find the right size helicoil kit (never used one before, not sure if i order the size of the original bolt, or have to tap larger and figure out what size coil to bring it back down to 18mm). no clue if this is feasible or a good long term fix or not.

4) remove the t-case, take it to someone to weld aluminum slugs into the hole and then tap the original 18mm threading back in. concerned with weakening the case. also time consuming - and this is my daily driver.

 

Ouch man.

I’m not sure about welding casings. Never had good luck with welding anything cast.

My vote is to pull it, split it, and tap it yourself. You can clean it all up and

 

Heli coil

 

Still have to tap that right?

 

Yeah, but the kit comes with the right tap. They are surprisingly strong. It will be stronger than the threads that were there.

 

I'd tap it and move up a bolt size. We use heli-coil at work quite a bit but mostly in holes that the screws or bolts seat into and pass thru. You'd still have to re-tap the hole for heli-coil, then you'd screw the coil in with the appropriate tool. The benefit of the coil is it takes the damage and is easily replaced once installed, you'd also be able to go back to the OEM bolt size.

 

Why not weld a bung to it? I don’t know if they make them that big but why not a valve that poor people use in their oil pans when they strip those? I can’t remember what they are called.

 

This is what I'm leaning towards - just tapping and going larger seems to have the fewest steps for me to screw up. Think i'm good to do it without removing the case and then flush it out before refilling to push out any stray aluminum shavings?

 

I coat my taps in grease to keep metal shavings from escaping. Might not get them all but it helps

 

Well, apparently, I am a dumbass. Hand tightened them and then took them a quarter turn with a wrench, figured that would be conservatively fine and that I would torque them down to spec after... finished up, grabbed the torque wrench, set it to 27 ft-lbs... and it just kept turning.

 

True and be careful to insure the threads are dry when you put it back it. If they're wet you can easily over torque it, even with a torque wrench.

Also, unfortunately this is what sucks about aluminum parts, even with a heli-coil in there you could still damage the threads again. It would be harder, but it's still possible.

 

Here is how you keep the shaving from going inside. Take the male part of an air compressor hose coupler and weld the end shut. Then drill a very small hole through the weld. Be careful not to break the drill bit off. Then hook it up to the air compressor and plumb it up to the transfer case vent. The air blasting out around the tap will blow the chips out.

 

Was the thread wet or did it have oil on it.

 

Also worth mentioning, whether you tap it out to the next size bigger or tap it and install a helicoil, the tap needs to go in absolutely, perfectly square. If it's tapped even the slightest amount crooked, the plug will leak. It's also possible that the threads on those plugs are not a common metric bolt thread pitch. They seem pretty fine for the size of the plug. I could be wrong though.

 

Thread was wet. That's enough to lead to over torque?

 

I'll preface this by stating that I used to be a machinist...

The only way to really "fix" this properly is to heli-coil the holes on a mill where you can properly bore out the previous jacked up threads, cut the new ones, and then take a really light (.007-.010) skim cut with an insert cutter to clean up the gasket surface while the entire thing is clamped down on the same setup. That way your bolt/gasket threads in perfectly perpendicular to your gasket surface. This would obviously require you to remove the cover and replace the gasket. It would take me about 30min to do both holes if you brought me the part all nasty with bits of gasket stuck to it. I'd need to clamp the thing down to the bed of a Bridgeport, get the appropriate tools ready. Tram in the first hole with an indicator/dowel pin, Drill/tap/skim cut and install the heli-coil and then I'd do the same to the other hole.

My old shop, the owner used to do stuff like this for people after hours or on lunch if we had a mill that wasn't tied up. Otherwise you wait. He'd charge you probably $85 or so although that's probably changed significantly as that was a decade ago.

You might be better off just ordering a new case cover and tossing it on.

 

I work at a machine/repair shop in my off season in the winter, although I only handle the elctrical stuff. we see this one covneyer belt gear boxes monthly. Either have it welded shut and re tapped, or drill and tap to a bigger size. We wont heli coil anything that holds back oil. I'm not saying you can't, but if you do go that route, just worry about sealing it. Heli coils are stronger than the original threads due to more surface area on the outer circumference.

 

Only thing I'd worry about is the fact that these thin, cast parts are usually relatively cheap, crappy aluminum, like 2024 or something and getting someone who can weld it up properly without warping the entire thing and wrecking your gasket seal could be a problem. If it's a big part that can absorb alot of heat that's one thing but a small thin thing like this might go all wonky like a pringle.

 

I don't have any experience with the heli coil but my vote goes to retapping the next size up. Just take your time and try to line the tap up as best as you can. If it begins to leak or seep I don't see why you couldn't add a crush washer, a felt washer, or even a little bit of RTV. Seems like you have nothing to loose at this point so might as well try something

 

What about some teflon tape wrapped around the threads?