Hey guys, hope y'all can give me some direction on this issue.

Went to change the transmission fluid this weekend, when I had removed the drain plug there were some threads from the aluminum transmission housing on the drain bolt from some jack@$$ that decided to over tighten the bolt. The drain bolt is a M18-1.50 thread size.

My question is - Can I simply drill out & re-tap the drain hole to a M-20 for a drain valve? Or should I drill & heli-coil back to the OEM spec?

Thanks!

 

I have had horrible luck with long term reliability of helicoils. I would rather drill and re-tapif its an option and if the housing can accept it.

 

Drill and tap for a 1/2" pipe plug, it'll work fine if you have access to pipe taps. Actually, you may be able to just tap it.

 

Mine did the same thing the only time I changed it. It had enough threads left in there so I put it back and it doesn't leak. Next time I remove it (If I ever do) I'm screwed.

I'm pretty sure there is plenty of meat around it though so you should be able to go the next size bigger. Just make sure no shavings are in the transmission.

 

It's patched until Friday, teflon tape is some good stuff, got a very slow drip right now. The O'Rielly's M-20 drain plug should work, looks like there's enough shoulder. Going to a buddy's auto shop this Friday to fix & install a set of 18" ROTA Torques!

I'll keep you guys posted as far as the fix.


Think I've decided not to go with the EZ Drain Valve, it would be sticking straight down. That would sure be a bad way to end a track day early......

 

why not simply clean out the threads back to oem spec m18?

 

1 - There aren't many threads left on the aluminum transmission housing.

2 - Would rather not use a heli-coil.

 

A half inch pipe thread takes a 23/32" tap drill.
A 20mm plug takes a 47/64, so I guess you'd be in good shape with that. Good luck to ya.

 

No material left to make m18 threads. If the couple threads left in there were to pull out as well the M18 plug would just slide in and out.

Would have to heli coil it, use one of those threaded inserts with some sealant on the outside or just go the next size bigger.

At 1/64 difference I would just stick with metric so you wont have to buy one standard wrench/socket just to work on the car.

I hate working on domestic vehicles because half of the bolts are standard and half are metric.

 

Rubber drain plug?

 

Luckily, we were able to save the OEM threads. Just ran a M18x1.50 tap through the threads and had enough meat left to torque the drain plug. Thanks for all the input.

 

-Hey, having the exact same problem with my transmission threads, I bought the same m20 plug from o reilys, did you have to tap it in or drill anything to put on that new m20 plug? I’m new to making new threads so just want to get an idea, thanks!