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Differential fluid change

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
239
Location
Michigan
Corvette
1977 light blue
I am preparing to replace the differential fluid in my 79 (Eaton). I've read some say always use GM additive, and I've also read using NAPA etc is fine also. Is there a real difference? Is there such a thing as too much additive? My plan is Valvoline GL5, plus NAPA additive. Input would be helpful.
 

Tom Bryant

Well-known member
Administrator
Joined
Nov 9, 2000
Messages
7,205
Location
Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
I've never used anything other than GM lubes. The part numbers have changed over the years but the product is what is recommended for a GM posi rear axle. If the other brands meet the same specifications they should be alright. I can't say from experience though.

GM AC Delco Axle Lubricant 89021669

GM AC Delco Fluid 88900330 Limited Slip Axle Lubricant Additive.
 

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
239
Location
Michigan
Corvette
1977 light blue
I've never used anything other than GM lubes. The part numbers have changed over the years but the product is what is recommended for a GM posi rear axle. If the other brands meet the same specifications they should be alright. I can't say from experience though.

GM AC Delco Axle Lubricant 89021669

GM AC Delco Fluid 88900330 Limited Slip Axle Lubricant Additive.

Thank you Tom, I ended up taking the big leap and used the NAPA stuff. The differential and posi work fine. Thanks again.
 

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