1970 GTO; What is best Posi Rear gear lube? - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 02-29-2012, 02:27 PM Thread Starter
 
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1970 GTO; What is best Posi Rear gear lube?

Hi All,

I have a 1970 GTO and I just changed the oil in my rear axle 3:55 posi limit diff. The problem is now the rear slips pretty badly in each gear. I used Mobil 1 75 -90W synthetic gear oil and GM posi additive, which were recommended by parts store. My mistake. The rear ran fine before I changed the oil so I'm going to change the oil again and hope that fixes the problem.

After reading other posts, my question is which rear oil should I use? And does it slip because I used synthetic or because I used 90 and not 140?

The most common answer I've read is to use either Torco rgo 75w 140 or Torco rgo 85w 140.

Any thoughts would be appreciated.

Last edited by TheBestVMan; 02-29-2012 at 03:06 PM. Reason: shorter tiltle
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post #2 of 3 (permalink) Old 02-29-2012, 04:10 PM
 
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Originally Posted by TheBestVMan View Post
Hi All,

I have a 1970 GTO and I just changed the oil in my rear axle 3:55 posi limit diff. The problem is now the rear slips pretty badly in each gear. I used Mobil 1 75 -90W synthetic gear oil and GM posi additive, which were recommended by parts store. My mistake. The rear ran fine before I changed the oil so I'm going to change the oil again and hope that fixes the problem.

After reading other posts, my question is which rear oil should I use? And does it slip because I used synthetic or because I used 90 and not 140?

The most common answer I've read is to use either Torco rgo 75w 140 or Torco rgo 85w 140.

Any thoughts would be appreciated.
lucas heavy duty high performance sae 80w-90 gear oil with 4oz. bottle of ac delco limited slip axle additive. that's the ticket. rickm
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post #3 of 3 (permalink) Old 02-29-2012, 06:35 PM
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I agree with rickm. Any heavy duty NON synthetic oil with the additive, and in 80w-90.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

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