Wrecked threads on torque converter drain plug hole

[KrisZ]

I would get a deburring drill bit, like this one from HD, stuff a rag in the hole it tape it up and make that clearance with the deburring bit.

After that you should be able to run a thread chaser or a tap on this thread and square it properly.

 

[paulo57509]

Can't tell how thick the bell housing is, but it appears there's already been an attempt to get drill/tap clearance. Is it possible to finish it off to get that clearance? Once you get the plug back in, I wouldn't ever remove it again.

Would any of these tools work?

https://www.mcmaster.com/products/thread-chasers/thread-location~internal/

 

[someonesomewhere]

I would get a deburring drill bit, like this one from HD, stuff a rag in the hole it tape it up and make that clearance with the deburring bit.

After that you should be able to run a thread chaser or a tap on this thread and square it properly.

View attachment 232322

Ftr, this is what you should have been using to create your clearance slot to begin with. From personal experience, trying to drill a hole that close to an edge is almost always a losing battle, especially under a car with weird access angles. But if you're going to, drilling small pilot holes and working your way up is advisable. Live and learn!

 

[oilylp]

Wow ! what is this in? I have not seen a TC drain plug in years.

This is from a 2014 Mercedes E350 wagon. This is a 7 speed and I think their current gen 9 speed box still has draining the TC as part of the service, too.

 

[Astro14]

Can't tell how thick the bell housing is, but it appears there's already been an attempt to get drill/tap clearance. Is it possible to finish it off to get that clearance? Once you get the plug back in, I wouldn't ever remove it again.

View attachment 232401

Would any of these tools work?

https://www.mcmaster.com/products/thread-chasers/thread-location~internal/

I don't think so. No room to work.

I would stick with a tap - that plug appears to have regular threads, so, a regular tap would work, if you can get it in there.

I would follow @Trav 's advice. Cover up the hole with a plug. Grind out your clearance. Just enough to get the tap in there. Grease in the flutes.

 

[oilylp]

Well, success everyone. This is what I had to notch out in order to get a M8x1.0 tap in square (the pitch is 1.0—I mistakenly said 1.25 earlier). The threads were salvaged/cleaned without too much fuss once I got it going. Since there was a burr almost right at the beginning of threading, I did have to take a bit of a leap of faith hoping I was in the original thread-path rather than forging a completely new one...

Yes I was a numbskull to not rotate the TC drain out of view before starting, but I should have just never done this in the first place. It was an "own-goal" and I was pretty mad at myself. The irony is that I did this service successfully 5 years ago and got the plug in and out despite the terrible angle! Live and learn. In the end, not that bad of a repair but it was pretty scary and I think I just needed confidence from hearing your guys' feedback to know that there was a path forward. Thank you all!

 

[The Critic]

This is from a 2014 Mercedes E350 wagon. This is a 7 speed and I think their current gen 9 speed box still has draining the TC as part of the service, too.

No one drains it at the dealer.

 

[JimPghPA]

FYI, if you can't find the tools you require, McMaster-Carr has everything. They have an online catalog.