It’s a long story, but during the process of changing the transmission fluid I damaged the threads of the torque converter drain hole badly and I can’t screw the plug back in (a running hand drill slipped and went into the hole). How can I repair the threads so that I don’t push metal shavings into the torque converter? Thanks for your help. I’m a bonehead.
Wrecked threads on torque converter drain plug hole
- Thread starter oilylp
- Start date
Grease on the drill bit/tap is the only method I know to keep shavings collected.
What size is it, picture of the carnage? You may be able to use a spiral flute tap, they bring the thread shavings and chips out of the hole but as you already had a go at it with a drill a magnet may be your best bet. Do not rotate the converter but just drag a strong magnet all around the hole and bring it to the hole so you can remove the junk with another magnet.
Time-sert or helicoil. Of the two, I would go helicoil, because it’s a bit lighter, and I wouldn’t want to add any real weight to the converter, or it will be a bit out of balance.
The Time-sert is the better option where great strength is needed, like repairing stripped head bolt holes in an aluminum block, but this is a drain plug, so, no real strength is needed.
A bit of grease in the flutes of the drill bit. Go very slowly. Grease in the threads of the tap. Go slowly. In fact, if you could just do the tap, and skip the bit, to minimize the chips created, that would be better. Drill/tap by hand, if possible, so that chips aren’t being flung under power. As an example, not knowing the ice, but if you can fit, say, a 15/64, do that, then go up to a 1/4, then a 17/64, etc. by hand each time so that you take out just a bit of material until you’re at the helicoil drill size.
Minimal depth of the helicoil so that it doesn't protrude farther into the converter than the plug did.
Gravity will be helping you, that is a tapered plug correct?
What size is the plug? pipe thread?
JHZR2
Staff member
I know a lot of these drain plugs in AT components can have issues. I don’t get how a hand drill slips and inserts itself into the open drain hole.
Pictures would be good. I agree with above. Time sert would be good but it may affect balance. Try to do a helicoil assuming there’s enough space.
I assume its a small drain plug like this TC drain on the older Mercedes transmissions?
If so there isn’t much meat to cut new threads, but it doesn’t take much torque to tighten either.
Pictures would be good. I agree with above. Time sert would be good but it may affect balance. Try to do a helicoil assuming there’s enough space.
I assume its a small drain plug like this TC drain on the older Mercedes transmissions?
If so there isn’t much meat to cut new threads, but it doesn’t take much torque to tighten either.
+1 There may or may not be enough meat there to do any sort of insert in which case a plug like the one you show can be used using a tapered pipe tap and plug, it can be inserted flush if done properly. A picture will be helpful
I was surprised that a time cert was considerably more expensive. A couple of years ago I had a spark plug eject itself from the top of the engine. I had a local reputable shop quote me for a helicoil and a time-cert. The helicoil job was $150 out the door. The shop had never time certed anything and said they'd have to buy the kit and it would be $700.
The thickness of the converter material would limit the thread repair choices. Try the least invasive method and from there.
The Time-SERT is a far more robust solution. The helicoil looks like a slinky, but the Time-sert is a complete insert. The depth is controlled, then the insert is expanded once in place, to lock it in as a permanent repair that equals or exceeds the strength of the original threads.
That’s why BMW uses it for repairs to head bolt threads in aluminum blocks.
For a Ford that spits spark plugs - with only a couple threads - I would have gone Time Sert.
To be fair to the shop, a kit is about $150. It includes a drill bit, a depth cutter, a specialized tap, and the installation tool that expands the insert. Each insert is a couple $$. But the repair is permanent, and strong.
https://www.timesert.com/
4WD
$50 site donor 2025
Yep - after that some ATF in a flex spout squirt can can finish up
Thanks for your responses everyone. A little more information: Basically the plug is not on the torque converter's equator, but maybe 15 or so away longitudinally. While the plug is within view of the bell house port hole, the plug's centerline does not intersect the hole making it tricky to get a tool on it. The plug is M8 x 1.25 with a 4mm hex head and I just barely got it out with a ball head key at a pretty extremely angle. To ease installation I wanted to drill a notch so that my hex key could be on axis—or at least a little more so.
Here's a picture of the damage. Do you think a tap or chaser rectify this? There's a nasty burr at the lip of the hole that may stop a tap from engaging. What's the best way to handle that?
And if you all have any other thoughts now that you can see what it looks like please let me know. Thanks everyone.
Here's a picture of the damage. Do you think a tap or chaser rectify this? There's a nasty burr at the lip of the hole that may stop a tap from engaging. What's the best way to handle that?
And if you all have any other thoughts now that you can see what it looks like please let me know. Thanks everyone.
Last edited:
I think the challenge with any repair is going to be getting it square.
This is a low-torque application - just enough to squish the copper sealing ring and not leak.
If it is possible, I would just hand turn a tap into it and see what you get. Coat the tap liberally with grease, so that the flutes are full and catch every shaving.
But with that tight clearance (the clearance which you were trying to fix with a drill), it’s going to be very difficult to get a tap to line up square. That’s your big challenge right there - keeping everything square.
If it is possible, I would just hand turn a tap into it and see what you get. Coat the tap liberally with grease, so that the flutes are full and catch every shaving.
But with that tight clearance (the clearance which you were trying to fix with a drill), it’s going to be very difficult to get a tap to line up square. That’s your big challenge right there - keeping everything square.
Wow ! what is this in? I have not seen a TC drain plug in years.
I see the hole saw didn't work but to do this job you need to create access. I would put a rubber plug in the hole and cut away just enough of the housing with a small cutoff wheel to get a straight shot at the hole, you can cover the cutout with a small aluminum plate. Check the size and thread of that bolt before trying to repair it, you may need a pipe thread, it looks like a course thread.
