I am not sure if my rear diff. plug is correct on my 65 vette. When I went to put the new repo. posi tag under the plug,it will not work. I think my plug should have a flanged lip on it to retain the tag like the 64. In my Paragon catalog there are no plugs for the 65, it stops at 64. Any suggestions?
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Re: Rear Differential Plug
Dick-----
The 63-64 and 65-79 differential filler plugs were different and they will NOT interchange; the threads are different. The 63-64 uses a straight thread with gasket and the 65+ uses an NPT thread with no gasket. The 65+ plug has an unthreaded "collar" area below the flanged head to ensure that there is a protected "seating" area for the filler tag. The 63-64 uses no such design. Both plugs have square heads and a flange, though.
The first thing that you want to do is to check the differential cover casting to see which one you have. It's possible that a 63-64 cover was installed sometime in the past. It's also possible that very early 65's used the 63-64 cover. If so, then the 63-64 filler plug would have to also be used. Most, if not all, 1965s used differential cover casting GM #3871375. If you have this cover, then the NPT style plug with unthreaded "collar" should work for you.
The 63-64 (and, possibly, very early 65) filler plug is GM #344829. The 65-79 plug is GM #3866433. Unfortunately, both are GM-discontinued. The 63-64 plug is reproduced; I don't know if the 65-79 is reproduced, or not. Also, if you aren't already aware, the 1965 filler tag was unique to that year.In Appreciation of John Hinckley -
Early '65's can be different
Joe has pretty well covered it, but just to show how weird it can get, here's what's on my original '65, VIN 01487. It has a 3818753-N carrier, AP 9 17 64, with a 3930303 cover and the '65-up tapered NPT plug. So it appears there was some cross-over where they were using up the 303's, but drilled to accept the later plug.
I have 2 detailed (500kB) pics I could email anyone interested.Comment
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Re: Rear Differential Plug
My cover cast number is indeed the 3871375 like Joe said. My plug does not have a flange on it, and has the letter W on its head. The diff. is definately a posi. So far I can't find the right plug. The car was built in the first week in Jan. 65. Thanks!Comment
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Re: Rear Differential Plug
Dick-----
If the plug has no flange on it then it's not an original plug and it's just some "generic" replacement that someone installed once-upon-a-time.
With the 3871375 cover you will definitely need the 65-79 style plug which, as I mentioned, is discontinued. Try Pacific Corvette (www.pacvette.com) for a good used one. Long Island might have a reproduction available.In Appreciation of John HinckleyComment
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Re: Early '65's can be different
wayne-----
I'm not surprised, at all, by that. In fact, based upon the research that I did, there were the kind of "vagueries" in the GM information that led me to believe that just exactly what you describe could have been the case. Actually, for 1965, I think that it's MUCH more likely that the '303' cover was used with the NPT plug (as yours is) than the '303' cover EVER being used with the earlier style plug. I couldn't be sure, though, so I didn't want to mention it. Now, we know.In Appreciation of John HinckleyComment
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