Finding the correct rear diff cover plug on these rears is difficult.   GM stocks them (9/13/2012) in their Vintage Parts warehouse.   They also stock the O/E gasket, which is a dual surfaced gasket.    I still have a Dorman part yet to arrive, which is quoted as a 3/4 inch plug.   P/N 090-062.   As soon as it comes in at Advance, I'll update this page.

(Prices below are a little discounted, local dealer gives our car club a little break and they treat us great!)

GM 'OE' Plug:  10033568  ($20.73)   ( no deal on price here, because it came from Vintage parts )

Gasket:  12523445  ($24.91)   ( again, a Vintage parts warehouse price )

Rear Gear Oil:  89021671  ($12.63)  x   2

Posi Fluid Additive:   88900330  ($12.63)  x 1

My old seal was leaking, and was loose in the hole, you could spin the plug from the outside with a little effort.    The stamped hole in the cover has an ID of 0.790.  Picture below is of the old seal protruding through the inside of the diff cover.

Best I can tell this is the original 1989 seal.  After carefully removing the old seal, you can see the seal has been removed pretty brutally over the years.   Look at the gouges in the sides.   The rubber was very hard.   Diameter of the sealing portion, just above the larger outside flair was 0.800 inches.   The larger flare just above that was 0.892 inches.    Notice the rough edges on the inside of the hole in the picture below, and the gouges in the OE plug.

l took a dremel and small file and smoothed those edges.

Picture of the new plug.   Diameter in the center, at the sealing surface was 0.857, on the flare above it was 0.949.   New plug was very pliable, bigger... just exactly right.

The GM gasket is a different material on each side, I put the 'salmon' colored smooth side toward the cover, and the thicker more pliable black side toward the differential.  ( hope I got that right, there was no info I could find to tell me)

The OE GM service manual lists this tool as the correct one to remove the plug.   I have something like this for removing GM door panels, not sure if it would work.   Definitely don't want to just pry this plug out with a screwdriver, unless of course you are replacing it and don't care.

Finished up by putting a thin coat of black RTV on the diff cover, put the gasket on, put a thin coat of the same RTV on the top of the gasket, and bolted it back up.    Put the posi-additive in, then 2 qts of GM gear oil and put the new plug in.    2 qts put the fluid just starting to come out of the bottom of the hole.   Perfect.

Works great!   Hope this helps. 

 -Gerry
 
 

gem 09/14/2012 10:00 AM