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Topic: what is the correct differential fluid to use?

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what is the correct differential fluid to use? (1/5)
 1/16/07 5:28pm
stevep316
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jersey city, NJ - USA

Vette(s):
1979 corvette metallic silver/red leather interior


Joined: 11/30/2003
Posts: 372

changing the diff fluid on my 79, but im not sure what grade diff fluid to use. also do i have to specifically use the gm posi additive, or would any brand posi additive (say from pep boys) do?

searched around the c3vr forums, but have not really found the specifics im looking for.

the haynes manual says to use a 80 to 90 weight oil gl-5 spec. most of what i find on the shelves are 75-90w, 85-140 and so on. i bought lucas 85-140.

would i make a mistake to use that?
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what is the correct differential fluid to use? (2/5)
 1/16/07 9:15pm
Karmel77Lifetime Member
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Clarksville, TN - USA

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1977 L48 T Top, Dark Blue


Joined: 10/22/2005
Posts: 258

 
Had my diff rebuilt this summer.  I went back with the recommended GM oil and additive.  $27.00 for the 2 qts of GM spec oil and additive.  You could do it cheaper but do you want to?ErmmErmmErmm
 
A good 90 weight probably wont hurt anything.  Mine sure is quiet thoughWink
 
My 2 cents!!
 
 
 
what is the correct differential fluid to use? (3/5)
 1/16/07 9:45pm
ranger3Lifetime Member
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North Charleston, SC - USA

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1975 L48 AT AC T-top


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Save yourself a lot of grief and buy the GM gear lube and the GM additive. The additive should go back in first, then add the lube up too the bottom of the filler hole. It is much easier to use an electric pump to remove the old stuff assuming you are not working an a fresh rebuild. If you are removing the old stuff, drive the car around the block first. It comes out much faster when it is warmed up. The GM additive seems to work the best at preventing posi-clutch pack chatter.
Once the new stuff is in, go to a parking lot and drive in circles with the wheel to the stop. Do it in one direction then go full stop in the other direction. This procedure will ensure that the disks in the clutch pack get the additive in the friction material.

Good luck,
Scott
what is the correct differential fluid to use? (4/5)
 1/17/07 9:31am
Adams' AppleLifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
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85/140 GL is too thick(unless you've got a truck diff in there!). Go with the 75/90, and the posi additive. I have used posi additive from LubeGuard, and it works quite well. (The GM stuff is easier to get, for most people.)

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what is the correct differential fluid to use? (5/5)
 1/17/07 5:19pm
stevep316
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jersey city, NJ - USA

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1979 corvette metallic silver/red leather interior


Joined: 11/30/2003
Posts: 372

thanks for the input guys- this is why im a c3vr member! Big%20smile

im going with the 75/90w and the gm posi lube
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