Differential Oil Replacement
Thread Starter
Racer
Joined: Jul 2000
Posts: 416
Likes: 4
From: Iron Mountain,Michigan
Differential Oil Replacement
Hello Fellow Vetteheads,
While replacing tank etc checked the oil in the differential and noticed it to be very black...how does one get it out ..should it be warm?..what oil and additive do I use to replace?
Thank You in Advance.
While replacing tank etc checked the oil in the differential and noticed it to be very black...how does one get it out ..should it be warm?..what oil and additive do I use to replace?
Thank You in Advance.
Burning Brakes
Joined: Mar 2012
Posts: 1,200
Likes: 1
From: Belle River Ontario
2015 C3 of Year Finalist
I just picked up a fluid transfer pump to do mine.
Princess auto 14 bucks
You should use genuine GM differential fluid and make sure to pick up a small posi additive as well.
Take the car for a short drive to warm up the fluid first, makes it easier to get it all out .
When I did mine I put the new fluid in a pail of hot water before opening them up to make putting in the new lube much easier
Good luck.
Princess auto 14 bucks
You should use genuine GM differential fluid and make sure to pick up a small posi additive as well.
Take the car for a short drive to warm up the fluid first, makes it easier to get it all out .
When I did mine I put the new fluid in a pail of hot water before opening them up to make putting in the new lube much easier
Good luck.
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
I'd be careful with the friction modifier additive. It's function is to allow more posi clutch plate slippage around tight turns, to help quiet things down. Problem is, stuff sometimes takes away a good amount straight line posi clutch pack lock up action, when you're really wanting it. Never use it myself. You can always add it later.
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
I'd be careful with the friction modifier additive. It's function is to allow more posi clutch plate slippage around tight turns, to help quiet things down. Problem is, stuff sometimes takes away a good amount straight line posi clutch pack lock up action, when you're really wanting it. Never use it myself. You can always add it later.
Use of the POSI additive is strongly recommended. 1 bottle per change.
Burning Brakes
Joined: Mar 2012
Posts: 1,200
Likes: 1
From: Belle River Ontario
2015 C3 of Year Finalist
Even do yourself a favor and do a "search" on this forum regarding differential fluid changes and you will see for yourself that the addition of a 4oz bottle of posi fluid is reccommended in virtually every post.
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Le Mans Master
Joined: Oct 2007
Posts: 7,445
Likes: 971
From: Tennessee/Rhode Island
75W-90 Mobil 1 synthetic with no friction modifier for 22 years now with zero issues. From my experience and others who have chimed in here and many times when this issue has come up in the past with fluid for the differential, it strongly appears that the friction modifier is NOT needed with synthetic gear oil. All of the fluids for these cars are so much better than 30-40 years ago with the advent of synthetic fluids that following the manufacturer recommendations from that era seems a little archaic, IMHO. Whatever you choose to do will work as long as there is nothing wrong with the diff.
Premium Supporting Vendor
Joined: Aug 2001
Posts: 5,364
Likes: 38
From: King George VA
AMSOIL Synthetic Gear Lube SAE 80w90 (Product Code AGLQT)
More than happy to the above for forum members at dealer wholesale pricing, about 25% below retail, via the AMSOIL Preferred Customer Program. Drop me a PM if interested.
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AMSOIL Preferred Customer Program (Members buy at Wholesale - a savings of about 25%)
C66 Racing #66 NASA ST2, SCCA T2
AMSOIL Dealer (Forum Vendor)
AMSOIL Preferred Customer Program (Members buy at Wholesale - a savings of about 25%)
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
As mentioned, you can always add stuff later, but not so easy taking it back out. My C6 ZO6 has a pretty noisy rear posi diff around tight turns, getting many owners to add the GM friction modifier. Really doesn't bother me, as road track the car, wanting all the perfomance advantage possible. Car came from the factory this way, and really not one to second guess the GM engineers.
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
I just changed rear end fluid today. You will need a device to suck the old fluid out. Also a device to put the new fluid in. I used a small pump that screws on to the gear oil bottles. I attached a clear hose to the pump so that I could see the fluid going in. Pump the fluid in until it starts to dribble out of the plug opening. I dropped my spare tire to give me better access to the fill plug. Everything should be easily available at your local auto parts store. By the way I used Amsoil synthetic Severe Duty Gear oil AND the Amsoil Limited Slip additive.
Burning Brakes
Joined: Jan 2001
Posts: 1,209
Likes: 438
From: Loir Valley Sarthe, France
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2024 C3 of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
I've done this job a few times, using different options re oil.
I now have rebuilt the diff and have gone back to teh tried and tested, and in my opion best option - GM oil and GM additive. I've found it works best, and lasts longer between changes.
For you guys in the US, obtaining it is easy. More difficult for us here in Europe, but worth the hassle as far as I'm concerned!
I now have rebuilt the diff and have gone back to teh tried and tested, and in my opion best option - GM oil and GM additive. I've found it works best, and lasts longer between changes.
For you guys in the US, obtaining it is easy. More difficult for us here in Europe, but worth the hassle as far as I'm concerned!
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
Another place to put the drain plug is under the bracket that holds the strut rods. Drill and tap 1/4" NPT just far enough to one side that you miss the ring gear. Make the hole on the bracket larger, of course, so you can easily insert/remove the plug..
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
I read somewhere that the models with aluminum housings were better left without a drilled and tapped drain plug. '80-'82s I believe. The housings tend to strip out when tightening a drain plug. Just some additional info to digest.
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Here is what 63mako uses:
AMSOIL Synthetic Gear Lube SAE 80w90 (Product Code AGLQT)
AMSOIL Synthetic Gear Lube SAE 80w90 (Product Code AGLQT)
