Recommended Gear Oil
Thread Starter
Instructor
Joined: Jun 2003
Posts: 139
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From: Salt Lake City, UT
Recommended Gear Oil
I need to replace both tranny and differential oil, and need some recommendations. I have the M-21 tranny. What type of gear oil should I use, brand and weight? Does the Chevy dealership still sell the posi additive?
Thanks, Mark
Thanks, Mark
Tech Contributor
Joined: Aug 1999
Posts: 15,130
Likes: 3,938
From: Connecticut, USA
The tranny and rear end use 90WT gear oil. Any Name brand will do or you can use the GM stuff. The additive should be the GM stuff though and is available from any GM dealership #1052358 about $7.00 a bottle.
Gary
Gary
Safety Car
Joined: Jun 2004
Posts: 4,652
Likes: 80
From: Lakeland Florida
For the differential I think it is 85W and the rating may be GL-5. And all the bulletins say to use 4oz. of the special anti slip differential lubricant.
Any ideas on how much oil the differential holds?
kdf
Any ideas on how much oil the differential holds?
kdf
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
I bought the GM differential lube along with the GM limited slip (aka posi) additive. It actually has a part# and I figured, why not use the GM stuff.
For the M20 trans I used a name brand gear oil - I can't even remember which. I tried synthetic, but I have since read in articles written by supposed experts that you are not supposed to use synthetic in an M20 trans that was built before the advent of synthetic oils. I can't remember the logical reason, but that is the recommendation FWIW.
For the M20 trans I used a name brand gear oil - I can't even remember which. I tried synthetic, but I have since read in articles written by supposed experts that you are not supposed to use synthetic in an M20 trans that was built before the advent of synthetic oils. I can't remember the logical reason, but that is the recommendation FWIW.
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Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by 1974slcvette
I need to replace both tranny and differential oil, and need some recommendations. I have the M-21 tranny. What type of gear oil should I use, brand and weight? Does the Chevy dealership still sell the posi additive?
Thanks, Mark
Thanks, Mark
Chevy does have the GM Posi lube - I have also purchased it (GM) at NAPA and CAP parts stores but apparently they don't all carry it.
Melting Slicks
Joined: Jan 2003
Posts: 2,165
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From: Where are the Smoky Mountain Cruisers? Not Correctly Restored Stingray
Originally Posted by PRNDL
I bought the GM differential lube along with the GM limited slip (aka posi) additive. It actually has a part# and I figured, why not use the GM stuff.
For the M20 trans I used a name brand gear oil - I can't even remember which. I tried synthetic, but I have since read in articles written by supposed experts that you are not supposed to use synthetic in an M20 trans that was built before the advent of synthetic oils. I can't remember the logical reason, but that is the recommendation FWIW.
For the M20 trans I used a name brand gear oil - I can't even remember which. I tried synthetic, but I have since read in articles written by supposed experts that you are not supposed to use synthetic in an M20 trans that was built before the advent of synthetic oils. I can't remember the logical reason, but that is the recommendation FWIW.
Penzoil 90W with GM additive in my differential.
No problems with either to date.
