1967 differential plug, why the gasket?

[Domenic T.]

I put the posi lube in my differential and put the gasket and tag on the plug thinking they would snug up and seal;

With about 50 lbs on the plug the gasket & tag were loose so I removed the plug and checked the TPI (threads per inch) on both surfaces to make sure I didn't mix up the plug with another diff here and they were both 14 TPI.

I brought the plug to the work bench and it is a taper plug that tightens just as pipe fittings do SO why the gasket?

My 63 diff has straight (fine) threads and will seal with a gasket, the 74 diff had a taper plug on it with sealer.

LIC says the gasket is for 63 to 67, that's a mistake isn't it?

If I tighten the plug with the red tag only, the tag floats around and would not last that long.

Whats the real story?

DOM

[Wayne M.]

Re: 1967 differential plug, why the gasket?

Dom -- the red posi tag is supposed to "float" ; in fact it rests on the top of the spring (unless you go over a bump). No gasket for NPT tapered thread plugs. If you have a cast ...375 rear cover it will use the taper plug, and 20 ft-lbs should seal without the shoulder of the plug touching the casting.

Pic below is of a '63-4 ....303 cover with fine (straight) thread. I show the taper plug alongside.

Now, just to confuse, I also show pics of a late ...303 cover with a coarse NPT thread (on my early '65). last shot is from the inside of the rear cover, showing coarse tapered threads.








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[Domenic T.]

Re: 1967 differential plug, why the gasket?

Wayne,
Thanks for clearing up things that bugged me.

Now that the car is going back as it was these small things like a gasket sold for NPT makes you wonder if something was changed before you got the car.

My diff #s do match so now thats done and on to the other.

DOM

[Timothy B.]

Re: 1967 differential plug, why the gasket?

Domenic

I just had the differental plug out of my 67 and the plug had a red colored gasket. My posi tag is missing so I need to find one if anyone can help.

I can get a picture tomorrow if you need to see the gasket.

[Domenic T.]

Re: 1967 differential plug, why the gasket?

Domenic

I just had the differental plug out of my 67 and the plug had a red colored gasket. My posi tag is missing so I need to find one if anyone can help.

I can get a picture tomorrow if you need to see the gasket.

Tim,
My tag came from LIC sec 02-07c (66-67) and was $8.00 .


DOM

[John H.]

Re: 1967 differential plug, why the gasket?

Domenic

I just had the differental plug out of my 67 and the plug had a red colored gasket. My posi tag is missing so I need to find one if anyone can help

Tim -

No gasket on a '67 - just the NPT plug and the free-floating red plastic Posi tag.


DiffPlug.JPG

[Timothy B.]

Re: 1967 differential plug, why the gasket?

Thanks for the information, I am going to pull the plug and check what Wayne posted about plug threads to see what's what.