Differential Fill Plug

[Philip A.]

My 69"s differential fill plug is seeping gear lube and noticed on a parts suppliers website there is a fill plug gasket. My question... is there supposed to be a gasket? Because i dont see where the gasket would press up against to seal with the red tag on the plug flange. Also on a 69 should the red tag read "use limited slip diff lubricant only" or "use positraction diff lubricant only"?

TIA

[E S.]

Re: Differential Fill Plug

IMG_20211018_175843229.jpgPhilip- Here is 69# 307xx- (filler plug has never been disturbed since delivery)
Red tag moves freely, there is no gasket, so the drain plug must "seal" when it runs out of threads.
There is a little seepage on this car also (5600 miles)
Hope this helps.
E.J.

[E S.]

Re: Differential Fill Plug

[ATTACH=CONFIG]108723[/ATTACH]Philip- Here is 69# 307xx- (filler plug has never been disturbed since delivery)
Red tag moves freely, there is no gasket, so the drain plug must "seal" when it runs out of threads.
There is a little seepage on this car also (5600 miles)
Hope this helps.
E.J.

Sorry- Trouble posting pictures

[Gary B.]

Re: Differential Fill Plug

Gary Ramadei explained in a previous post that from 1965 onward the rear diff plug had 3/4 npt (pipe threads) and there is no gasket. Gary recommended Permatex #2 on the threads to decrease the likelihood or the volume of leakage. Others have suggested Permatex Ultra Black, which is the most oil resistant.

Things would be different if someone converted your fill plug to a machine thread from the pipe thread.

Gary

[E S.]

Re: Differential Fill Plug

Really? Converted fill plug threads and gasket sealer?
I thought the criteria is TFP?

[Gary B.]

[E S.]

Re: Differential Fill Plug

Understood- Not wanting to "fool" anyone- just to document how things were.

[Philip A.]

Re: Differential Fill Plug

Thanks E.J. Thanks for the pic.
Unfortunately mine is seeping till the point of almost a drip and dont understand why. I also dont know why a gasket is even offered unless they mislabeled it on the website and it should be for a different year. Guess i'll use a smidge of gasket sealer #2.
Thanks again.

[Philip A.]

Re: Differential Fill Plug

Thanks E.J. Thanks for the pic.
Unfortunately mine is seeping till the point of almost a drip and dont understand why. I never known a diff fill plug to ever have a gasket so that is what threw me. I also dont know why a gasket is even offered unless they mislabeled it on the website and it should be for a different year. Guess i'll use a smidge of gasket sealer #2.
Thanks again.

[Gary R.]

Re: Differential Fill Plug

The 63-4 covers had a machine thread and I believe a leather gasket. As Gary mentioned, by 65 the revision was made to 3/4npt threads. In theory the plug should seal as is but over time oil may weep out. When I build a diff I use teflon tape to ship it back and #2 Permatex will also work as a thread sealant. I have used it for 45 years. One thing not to use is the white High temp Permatex thread sealant. This works great to seal but it also works like a thread locker. I use it on the steering box adjuster nuts to seal and lock in the preload but don't use it on the diff plug. The original plugs have a flange head to hold the posi tag but any 3/4 plug will work. Some of the originals had a W in them and others were plain.