In a jam: Stripped transmission fill plug…

Your picture is focused on the Allen wrench in front of the "stripped" drain bolt, so I can't say for sure, but it looks like the Allen key wasn't seated in all the way when you "buggered it up".

If only the top bit of the drain bolt is buggered, perhaps you can take a small file and remove the bent bits of metal that is preventing the Allen socket from going in all the way into the drain bolt hex opening? Or, tap the socket into the hex opening with a hammer to see if it will bottom out in the drain bolt.

Make sure that the hex socket is 10mm and fits snugly, so the hex opening isn't rounded. If it fits loosely, you can shim the hex socket with some thin metal strips maybe so the fit is nice and snug before trying to apply any torque to the drain bolt.

Also, you should probably apply some PB Blaster or similar penetrating oil to see if you can pre loosen the stuck bolt.

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The only sure way to remove that plug (once this happens) is to weld a nut onto it. I would look around in your area and try to find a mobile welder. Or plan to have the vehicle towed to a shop that is capable of handling this.

You can try the splined extractors or a torx bit, but they rarely work.

Also, it is normal for that plug to be very tight. It is due to the dissimilar metals between the plug and the case. Do not use anti seize, it will contaminate the oil. Next time, use a quality socket and a long enough ratchet.

 

A few things you can try...
Use valve grinding compound on the Hex socket and some in the plug.

Try to line it up straight and tap it in with a hammer. Then put the breaker bar on it.
The larger the better for leverage. Slowly start applying counter clockwise pressure and
start tapping on the back on the breaker bar where the socket attaches.
Hopefully, it will start backing out. With the right amount pressure from the hammer, it might
pop free.
If it doesn't work, you can try a chisel and hammer at about a 30 degree angle and hopefully
get it out. I've done this both ways and both have worked for me.
They also make larger easy outs that you can hammer in that bite the plug and hopefully get it out.

 

The plug is made of steel, not a die cast zinc alloy like Zamak .

This is the method we have used for many years in the aerospace industry.

I would not use heat or weld a nut on the plug as any heat above 500 degrees F would damage the aluminum alloy case.

I would use a tapered broken or damaged bolt extractor like these.

https://www.northerntool.com/shop/tools/product_200685157_200685157

Since the plug is steel, a magnet can be used to catch the drilling residue. I would stop drilling when the bit is about to break through.

Then, i would carefully hammer the tapered extractor through the plug and wrench it out.

As for myself, I have replaced both the fill and drain plug with M18x1.5 aluminum magnet drain plugs. They install and remove with either a 19mm socket or wrench,

 

^ This. I used a 19” long, 1/2” drive ratchet, and a Stanley 10 mm hex driver, with a 1/2” to 3/8” adapter. The long handle allows more control, reduces your effort.

 

Do you honestly expect you'll ever be in there again?

Given that the ATF is rated for lifetime service, you're already pretty deep into voluntary "over-maintenance" for a 10 year old car.

 

Maybe brush bolt threads and the washer with transaxle fluid.

Then, specified torque is 29 ft/lb: back off a bit, to say 25?

 

After I get this out anti-seize on the threads is the norm and I never put it back in that tight absolutely no need seriously just like oil filters I don't let people install them I change my own oil because some boob will put on the oil filter so tight just because that's what they think they need me doing when we allow people to think that they need to be doing something we have a problem so I don't allow this that's why I don't allow people to touch the car generally speaking pull an engine for me sure but change my oil and regular maintenance not likely people get in a hurry make foolish mistakes and then you're paying

 

?? See post #4....
And do not over tighten it...

 

Yeah ... that's a kind of "impact" that works magic in these situations. Not the kind from an impact wrench (which uses impact to create large shock torque that can twist things into pieces or round off heads). Just the kind that bops straight down on the axis of the fastener, and breaks the corrosion bonds between the threads.

That chisel and hammer were doing more than just making a screwdriver slot. That's why it spun out like it was brand new after that.

For what it's worth, Lisle sells a "seized fastener removal kit" that works on the same principle. It's used with an air hammer, just to gently (light touch on that trigger!) and rapidly keep bopping straight down on the fastener, while you just use a normal wrench and hand pressure to turn the tool counterclockwise. Thexton sells a similar tool also.

 

I'm guessing "1/2-to-full turn" after hand-tight would be way more than "snug" for that plug, and probably way more than the specified torque in the manual.

The kinds of things where you can put that much rotation on, after bottoming out by hand, are either things like oil filters, with a rubbery gasket that gives, or things like head bolts, where you're officially expected to stretch them. Or tapered pipe threads in plumbing. This plug fits none of those descriptions.

I'd just get a new, non-mangled plug and washer, and put it back in to the specified torque, and call it a day.

 

Decent quality, micrometer style torque wrenches are cheap, around $30. 3/8" size would be good for the fill/drain bolt spec (29 ft/lb). A set of 3, 1/2", 3/8" and 1/4" will all come in handy.

 

It just needs to be a snug fit. I use a 6 inch ratchet to tighten it up.
Then a 12 inch breaker bar to give it a snug tweak, about a 1/4 turn, maybe an 1/8.
You could use a torque wrench, and go maybe 5# under what it says. There isn't any
pressure on it to get forced out.