Guest taongisurvivor Posted October 8, 2015 Share Posted October 8, 2015 Getting ready to re-install the posi-differential back into the 67 Riviera GS. The dustless blasting, primer, and re-paint went better than expected and the differential is really, really beautiful. All new bushings, brake lines, wheel cylinders, and shocks. I now want to change out the diff fluid and was planning to use Amsoil synthetic plus a bottle of GM posi additive. Is this combination acceptable??? Link to comment Share on other sites More sharing options...
rocky5517 Posted October 8, 2015 Share Posted October 8, 2015 I've heard that there is a different fluid for the posi's- better check with an expert Link to comment Share on other sites More sharing options...
JZRIV Posted October 8, 2015 Share Posted October 8, 2015 (edited) Use mineral based 80/90 gear lube with the GM additive. Of course there may be varying opinions since its an oil related question. My take is the clutch plates were designed for this oil in mind when synthetic wasn't around. I know some have used synthetic and it may be OK. Results could depend on the condition of the clutch plates. Goal being to reduce friction just enough so no chattering when hot but not so much that it makes the limited slip....too slippy. Edited October 8, 2015 by JZRIV (see edit history) Link to comment Share on other sites More sharing options...
RoadShark Posted October 8, 2015 Share Posted October 8, 2015 I would buy API GL-5 rated fluid of the type JZRIV mentioned. Link to comment Share on other sites More sharing options...
Guest taongisurvivor Posted October 10, 2015 Share Posted October 10, 2015 I called AMSOIL and they said the standard 75W-90 gear oil is perfect for the positraction differentials. The oil has been formulated to include the anti-chatter additive. They stated that no additional additive is necessary. We'll see tomorrow. Link to comment Share on other sites More sharing options...
70rivme Posted October 10, 2015 Share Posted October 10, 2015 Just completed the 3.08 differential/posi swap on my '70 last night and took it for a spin with no issues. I will take it for a longer cruise today though to be 110% sure. As far as oil goes, I used Supertech 80/90 WT from Walmart along with the 4oz of GM limited slip additive. I used the same 80/90 to coat all of the new clutches prior to assembly as well. I am not too sure about putting a synthetic in there, but with as much time and effort I put into this project I will take the recommended conventional any day. Good luck! Link to comment Share on other sites More sharing options...
RoadShark Posted October 10, 2015 Share Posted October 10, 2015 I just changed the fluid in mine. I put this in: http://www.redlineoil.com/product.aspx?pid=133&pcid=4 Any modern GL-5 oil is light years ahead of what was put in at the factory 50 years ago. 1 Link to comment Share on other sites More sharing options...
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