tomard

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.

CASAvette

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.

noonie

Here is one from a recent thread.

tomard

Is that plug in the cover or the differential case???

I'm Batman

Instructions have been posted before.

http://forums.corvetteforum.com/show....php?t=1603168

jontis

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.

GTR1999

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.

Sabbath1979

So you are saying that is ok to install a plug in an iron unit with brass, I suppose the thread fit matters, but if this is aluminum, it seems to work a bit but the threads with fail?

Twin_Turbo

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)

GTR1999

I've seen threads pull from a few aluminum(non-vette cases). I have tapped my old muncie like this 30 years ago without a problem. For the 80-82, Marck is more familar with these diff's then I am. I do not work on them at all. If indeed they are a thin as Marck says then I would not tap them. The iron units have about .250-.300 thickness to them where I tap them and do not leak.
Good point Marck, thanks for the heads up.