Installing Differential Drain Plug
Thread Starter
Racer
Joined: Jul 2005
Posts: 420
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From: Yerington NV
Installing Differential Drain Plug
I want to change rear end fluids on my 80, and since I have to practically tear the entire car down, I was thinking about having a drain plug installed on differential cover while in there.
Does anyone have pictures of their drain plug locations and any advice you have about doing it? I was planning on taking it to machine shop that can drill/tap it, and use a magnetic drain plug.
Does anyone have pictures of their drain plug locations and any advice you have about doing it? I was planning on taking it to machine shop that can drill/tap it, and use a magnetic drain plug.
Heel & Toe
Joined: Jun 2006
Posts: 19
Likes: 0
I don't have pics, but I just had this done a couple of months ago on my '78. The mechanic I used knew his stuff (which of course is why I used him in the first place)--he drilled out (countersunk) a larger area in the bottom of the case at first; then switched to a smaller bit for punching though for the actual hole itself. This approach allows better/easier access for a socket or other wrench to grip the drain plug.
He tapped it and used a 1/8" brass pipe plug to seal it up. Works like a charm--not a drop has leaked.
He also stuck a magnetic wand up into the (drained) case to get any stray bits of metal that the drilling might have deposited there--as well as to capture any loose metal that hadn't been emptied out with the old fluid.
Now, changing the diff fluid will be a (relatively!) simple matter of hoisting the rear end, removing the pipe plug and the filler plug, draining, and pumping in the new.
One of the aftermarket suppliers offers a 'kit' to do this--it includes a template for the plug location. Sorry but I don't remember which one. I think it might be Mid-America or Corvette America.
He tapped it and used a 1/8" brass pipe plug to seal it up. Works like a charm--not a drop has leaked.
He also stuck a magnetic wand up into the (drained) case to get any stray bits of metal that the drilling might have deposited there--as well as to capture any loose metal that hadn't been emptied out with the old fluid.
Now, changing the diff fluid will be a (relatively!) simple matter of hoisting the rear end, removing the pipe plug and the filler plug, draining, and pumping in the new.
One of the aftermarket suppliers offers a 'kit' to do this--it includes a template for the plug location. Sorry but I don't remember which one. I think it might be Mid-America or Corvette America.
Team Owner
Joined: Oct 2004
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From: Springfield MO
St. Jude Donor '07
Instructor
Joined: Apr 2005
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That picture is from Gary's posts and the oil plug is in the differential housing (the case, not the cover), in it's lowest part. That channel is the only place you can locate the plug if you want all oil to drain without tilting the pumpkin. I just drilled and tapped that location in my own brand new restored rear end and it feels good so far but man I was nervous when I did it.
Tech Contributor
Joined: Aug 1999
Posts: 15,205
Likes: 4,034
From: Connecticut, USA
That picture is of one I did in an iron unit. For an aluminum unit I would also use that setup. The use of just a brass plug will, over time, strip the threads out of the aluminum. Usings a 1/4 npt x 1/8 npt bushing will allow you to use the 1/8 plug to drain without loading the threads on the 1/4 npt hole. Your guy was close but not close enough. Now you can tell him how to do it the right way. I wonder if I'll see this end up in vette magazine in the future?
Tapping a iron diff is ok to use the plug, as the brass is not going to strip out the threads.
Tapping a iron diff is ok to use the plug, as the brass is not going to strip out the threads.
6th Gear
Joined: Mar 2007
Posts: 6
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From: 25 Miles from Madison Wisconsin
That picture is of one I did in an iron unit. For an aluminum unit I would also use that setup. The use of just a brass plug will, over time, strip the threads out of the aluminum. Usings a 1/4 npt x 1/8 npt bushing will allow you to use the 1/8 plug to drain without loading the threads on the 1/4 npt hole. Your guy was close but not close enough. Now you can tell him how to do it the right way. I wonder if I'll see this end up in vette magazine in the future?
Tapping a iron diff is ok to use the plug, as the brass is not going to strip out the threads.
Tapping a iron diff is ok to use the plug, as the brass is not going to strip out the threads.
Last edited by Sabbath1979; Mar 14, 2007 at 06:47 PM.
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Brett Foote
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DO NOT drill the 80-82 diff for a plug like that. It will leak..guaranteed. The case is not thick or strong enough there for a pug. What you need to do is fabicate a small plate that has a bung for a plug, then drill the case for the bung to fit through and secure this w/ sealant and 4 machine screws on the sides or even use epoxy adhesive (or have someone tig weld a bung to the case, that would be the cleanest solution)
Tech Contributor
Joined: Aug 1999
Posts: 15,205
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From: Connecticut, USA
Good point Marck, thanks for the heads up.
