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Installing A Torque Converter Drain Plug

Mar 9, 2009
Torque converter drain plugs are really nice to have because you can completely drain your torque converter whenever you change your transmission fluid. All you need to install one is set your C3 on safety stands high enough to allow you to EASILY drill an 1/8" pilot hole in the middle of the "band" where two halves are welded together. Here's the step-by-step procedure:

1. Drill an 1/8" pilot hole thru the middle of the band where the two halves are welded together. It'll begin leaking the moment the 1/8" bit breaks thru so have a drain pan ready to catch the ATF. To make it easier to know where your drain plug will be I recommend drilling the hole in alignment with the middle torque converter/flex plate bolt. When I say "middle" I'm referring to the single round hole (one hole is round and the other two holes are oval).

2. Drill an 11/32" hole thru the band.

3. Using an 1/8" NPT tap cut threads JUST deep enough for a 1/8" Allen head pipe plug to be screwed in with about 3/32" to 1/8" sticking out. If your tap bottoms out before the threads are cut deep enough use a 2nd tap that has been shortened about 1/4" to cut another 2-3 threads.

4. De-burr the inside of the tapped hole with a tiny pin file then use a small magnet to remove any tiny cuttings that remain.

5. Install the pipe plug with red LocTite on it and tighten TIGHT to prevent leakage.

6. Spray white or bright yellow paint onto the drain plug and surrounding area so the drain plug can be found easily.

That's all that is needed. I put two square head drain plugs in my TH700R4's torque converter spaced 180 degrees apart so I don't have to turn it as far to drain it but one plug is all that is needed. I'll take a picture of my torque converter tomorrow morning so you can see the finished installation. Over the last 50 years I have installed 1/8" NPT drain plugs in all of my torque converters except my '68 Plymouth as it already had two 1/8" NPT drain plugs with 7/16" hex heads from the factory.
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