1980 rear differential lube
Thread Starter
Instructor
Joined: Jul 2011
Posts: 109
Likes: 3
1980 rear differential lube
I am slowly changing fluids and oils on my 1980, rear differential is next, is the original GM oil still available (89021671) and (88900330)posi additive? If not what is next, I would like to keep it all GM if possible.
Le Mans Master
Joined: Jun 2019
Posts: 7,658
Likes: 2,470
From: Indiana
I got both from local gmc dealer
luckily the younger guy just stared at me and a more experienced gent explaned what it was...wasnt cheap, i used two bottles additive as some recommended here
luckily the younger guy just stared at me and a more experienced gent explaned what it was...wasnt cheap, i used two bottles additive as some recommended here
Last edited by interpon; Sep 4, 2020 at 06:55 PM.
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
The GM posi additive is certainly available and at places other than a GM dealer. Not sure about the gear oil.
I don't believe an '80 has a drain plug for the differential unless perhaps someone tapped one in. If no lower drain plug you need a "transfer pump" to suck the fluid out via the fill plug. They're cheap.
Prepare for a filthy and hideously smelling job! No joke--wear clothing you intend to throw away!
I don't believe an '80 has a drain plug for the differential unless perhaps someone tapped one in. If no lower drain plug you need a "transfer pump" to suck the fluid out via the fill plug. They're cheap.
Prepare for a filthy and hideously smelling job! No joke--wear clothing you intend to throw away!
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Good for you sticking with the "tried & true" for 40+ yrs: GM Lube.
Summit has it. Amazon has it, as well as Muskegon Brake. You will need two large bottles of GM lube and 1-2 small bottles of GM Posi modifier.
Shop around for the best price w/ shpg.
I highly recommend mixing the two lubes in a container, then pour that into a condiment squeeze bottle found at food supply stores (Gordons). It will take a few batches to fill the diffy, but will be premixed.
Summit has it. Amazon has it, as well as Muskegon Brake. You will need two large bottles of GM lube and 1-2 small bottles of GM Posi modifier.
Shop around for the best price w/ shpg.
I highly recommend mixing the two lubes in a container, then pour that into a condiment squeeze bottle found at food supply stores (Gordons). It will take a few batches to fill the diffy, but will be premixed.
