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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.
 

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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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