Transfer Case Drain Plug Problem - Defender Source
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  #1  
Old October 17th, 2010, 07:26 PM
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Keith Zack
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Transfer Case Drain Plug Problem

I have a new to me 90 and changed all the fluids today. This brought about one problem. I removed the transfer case drain plug. It was neither unusually hard or easy to remove, seemed quite normal. Once removed, I noticed metal coils stuck in the threads of the plug. On re-install the plug turned easily and would never tighten against the case. It is now apparent that it was cross threaded or overtightened by the previous owner or for some other reason the threads failed on the case. The threads on the plug are fine, but the threads on the case are basically gone.

So, what should I do? Can I find a similar style plug with a magnetic end with a larger diameter thread and re-tap the hole in the case to this new thread size? Does anyone know of where I'd find this new size drain plug? Could I just use a larger diameter bolt? Some other idea?

Thanks, Keith
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  #2  
Old October 17th, 2010, 10:25 PM
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helicoil or other thread repair. or 2nd hand cover from a "parts" case
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  #3  
Old October 18th, 2010, 08:16 AM
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re-tap the thread making sure your tap is straight, it's worth the try before you get into more complicated stuff.
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Old October 18th, 2010, 08:33 AM
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Thanks guys,

I did put the plug back in with hylomar on it and drove it about 30 miles without any leaks, but I am not comfortable with this. This helicoil options seems to be a good idea. Anyone know the thread size of the plug? I could buy the helicoil kit for that size and give it a try. Anyone use the helicoil kit before?

Thanks, Keith
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Old October 18th, 2010, 10:20 AM
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you should find the thread size and pitch somewhere on the forum. For taps check etaps.com
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Old October 18th, 2010, 01:37 PM
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I would not use a stripped plug like that. There is potential for it to vibrate and fall out or for the sealant to break down and lose its grip. Better to use a temporary emergency type expanding plug found at any auto parts store. You can swap between plugs without losing too much oil, a bit messy but better than wasting all that oil.

When you go to do the permanent repair you'll need to drain the oil obviously. If you are seeing a coil of alloy in the threads of the drain plug then simply retapping will not suffice. Call around, check all the parts books, etc and you will eventually find the thread size info, or maybe someone here will know. Or perhaps LR4x4.com. Seem to recall that being a topic somewhere. I still think a whole new cover will be the best route to go, as you will probably want to take the old one off to fix it anyway.
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Old October 18th, 2010, 02:22 PM
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Thanks for the help. From what I can find it is an M12x1.5. Hopefully I can find the helicoil or equivelant locally tonight. It's not a daily driver so not worried about losing the plug as it is sitting in the garage. I plan to at least give it go with the helicoil with the transfer case left in place.

Thanks, Keith
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  #8  
Old October 18th, 2010, 07:06 PM
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Tap it to the next size larger NPT size. American thread.

Nest time drain the case through the middle bottom cover bolt. The 8mm bolt with a 10mm head. thse drain plugs are a ticking time bomb.
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Old October 18th, 2010, 11:27 PM
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Quote:
Originally Posted by pendy View Post
Tap it to the next size larger NPT size. American thread.

Nest time drain the case through the middle bottom cover bolt. The 8mm bolt with a 10mm head. thse drain plugs are a ticking time bomb.
Why does this happen to these cases?

Jim, which bolt is it? See the picture.
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  #10  
Old October 19th, 2010, 06:55 AM
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Why does this happen to these cases?

Simple answer, steel drain plug in an aluminum case without an insert--must always torque to factory specs, any over torquing will likely lead to stripped threads. I would go the helicoil route --the insert will give it the strongest case-to-bolt interface. This is why with companies like Ferrari, all threaded interfaces into the engine block use inserts, such as helicoil. In fact, the aerospace world uses inserts since after a preset number of bolt-to-panel mates, each of which weakens the interface, the insert can be removed and replaced.
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Old October 21st, 2010, 08:14 AM
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Just in case anyone is interested for future reference....

I simply tapped the hole in the case to 1/2-20 thread. Being particularly careful to keep the tap straight with the original hole. I did not need to drill it out at all, just ran the tap through (which I had on hand). The local autoparts store has 1/2-20 magnetic drain plugs on the shelf for $2. It tightened nicely and seeled completely. Test of time will tell for sure.

Thanks, Keith
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