Stripped Transmission Pan Drain Plug

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Dad has a 92 Toyota Previa. There's a M10 bolt in the steel transmission pan. I know in the past, the dealer has installed it super-tight. However, I have drained/refilled the transmission pan twice since that incident, and IIRC, it was fine both times.

This time, I went to remove the drain plug and it would not come out. It feels like it is sticky/stuck in there, so I am guessing that the threads are toast? I ended up changing the trans fluid through the cooler lines anyway.

I am guessing that the plug has been stripped since it was last touched (which was 3 yr and 48k ago), but has not leaked. With all the twisting/turning which occurred today, is the plug now going to leak since I "disturbed" it?

What is the best way to fix this problem? My first thought was to just order a new tranny pan since they are under $80. However, if a tap will not leave a bunch of shavings in the pan, then I'm open to the idea as well.

Thanks.
 
Does it twist left (to loosen) but gives a lot of resistance? If so, yes, the threads are likely ruined. If it doesn't move at all to the left (to loosen), it could just be that you need to pop it loose with an impact driver. It's amazing what the tapping action of an impact can do to a hard-to-break bolt.

I'd probably order a new pan myself.
 
Just hit the wrench or ratchet handle (i keep an old Craftsman for beating on) with a dead blow hammer using quick short raps, it will probably come right out.
The worst thing you can do with a stuck or rusted nut or bolt is apply a lot of torque to it. Shocking it loose is the way to go.
 
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Another thought: if removing the pan to install a new one isn't a big deal to you, just remove the pan to tap new threads. No issues then with metal debris.
 
There appears to be an epidemic of over tightening nuts, bolts and oil filters among young mechanics. AT a shop the other day I watched a young mechanic get stuck pounding a long screwdriver through an oil filter to get it to start turning. He changed he oil and then what did he do. He got out the oil filter wrench and really pulled hard to make sure the filter with tight. So, in effect he is just doing to the next mechanic what the last one did to him. He also put the gorilla arm on the oil drain plug, too. I don't think this mechanic has any idea what the proper torque would be for various fasteners, spark plugs and oil filters.
 
Had a 91 Corolla with the 10mm allen bolt. My first Brand New car.
The local tranny shop had stripped the bolt, probably with a SAE allen wrench.
So my first DIY ATF change was with a stripped bolt. I removed the pan got the file out and filled two opposing flats on the bolt and broke it free with a wrench. Dealer had new bolt and washer for less than $15.

This ordeal sold me on DIY.
 
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If the threads on the pan are really messed up, running a tap through there will not fix it. Taps are for cutting new threads in a properly sized hole and thread chasers are for cleaning up moderately damaged threads. If they are stripped then the hole is now to big and the plug will not seal properly.

And people may disagree but I would never attempt to re-thread an oil pan while still on the car. You might but I wouldn't. I would be too worried of metal chips remaining in the pan.
 
Originally Posted By: kschachn
If they are stripped then the hole is now to big and the plug will not seal properly.


If it's a regular drain plug with a gasket, the threads have no role in sealing. As long as they hold while tightening the plug, they are fine.

Light alloy transmission cases often have pipe threads. This is a steel pan with M10 threads, which suggests a regular plug using an aluminum or copper washer as a gasket.

The sealing is done entirely by deforming the gasket washer to fill in the sealing surfaces. The plug isn't a regular bolt, it has a smooth surface under the head which may be slightly conical. The gasket is soft copper or aluminum (it's not common to see fiber or plastic on a transmission).

It's important to replace the gaskets. You might get two or three uses, but they harden each time they are deformed. Soft aluminum also rapidly age hardens, getting more brittle just sitting at room temperature. A hard gasket won't seal easily, and will make the plug extra difficult to remove (which may have been what happened here).
 
I think the problem with over tightening is places do not use a new washer and excessively tighten to compensate.

For the filter I never use a wrench. As tight as my 2 hands can get it seems to work fine.
 
Originally Posted By: kschachn
If the threads on the pan are really messed up, running a tap through there will not fix it. Taps are for cutting new threads in a properly sized hole and thread chasers are for cleaning up moderately damaged threads. If they are stripped then the hole is now to big and the plug will not seal properly.

And people may disagree but I would never attempt to re-thread an oil pan while still on the car. You might but I wouldn't. I would be too worried of metal chips remaining in the pan.


Grease the tap and go over it with a strong magnet afterward. You wouldn't pull the head to re thread every Ford mod that blew a plug out. A few small chips even if they got left in there are not getting into the oiling system, it would have to get past the screen and filter first.

On many vehicles the engine needs to come out to remove the pan so in that case just replace it 19hrs labor later in some cases.

Edit: I am talking about an engine oil pan, i would probably pull a tranny pan if it was easy enough.
 
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Save the old fluid and if you can re-thread it and goes well use the old fluid as a flush pour it and it will drag out most if not all the shavings and if you filter this same old fluid with an old t-shirt you can re flush it as many times as you want.
 
Thanks guys. Here's what I've compiled so far. The drain plug on these pans is extremely easy to strip - the torque spec is only 14 ft-lbs. So, a few "cycles" where the plug was a bit overtightened will probably do it.

With that said, the factory bolt is a M10x1.5. There does not appear to be enough space to tap for a M12 bolt. Some others have mentioned moving to a SAE size but neither myself nor a friend has a set of SAE taps. Others have been lucky and have been able to just get a new bolt, and clean up the existing pan threads with a M10x1.5 tap.

One of my friends suggested that we clean up the pan's threads as best as possible, get a new M10x1.5 bolt, and use a locking washer + nut (via the inside of the pan) to "lock" the assembly in place. I'm still trying to understand how this would prevent fluid from leaking, but his thought is that this should at least keep the bolt secure.

From what I can see, all of these solutions have the potential to be successful, but may not be a true 100% fix. I'm really starting to like the idea of buying a new pan for $100 or so and fixing it for good.
 
Originally Posted By: The Critic
I'm really starting to like the idea of buying a new pan for $100 or so and fixing it for good.


That's what I'd do and be done with it for good.
 
Originally Posted By: demarpaint
Originally Posted By: The Critic
I'm really starting to like the idea of buying a new pan for $100 or so and fixing it for good.


That's what I'd do and be done with it for good.


Yup, if the car is worth it and will be kept for a while longer, it's probably the safest solution.
 
Update: ended up buying a new pan. I tried many different methods, but the old plug just would not come out of the pan.

Cost of a new OE pan and pan gasket, with my discount, totaled about $150. At least it's now fixed properly...
 
Originally Posted By: michaelluscher
I'd have held the dealer's service department liable...


He's done it twice since the dealer touched it.
 
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