I need assistance on what rear gear oil to use? The 1972 Buick Manual says "TL SAE 90" for limited slip. What can I buy in 2005???? Thanks in Advance! Also, any mechanics in the Rockford, IL area that know these cars, I have a few things I need done.
Coastal or Valvoline 80-90 is what many parts & discount stores carry. With your oem 8.5 posi rear, 2 qts of 80-90 & small bottle of GM posi additive is what you need. Shy away from synthetic gear lubes with built in limited slip additive. Also do not substitute autoparts store posi additives like the blue paste in a tube or the $13 Moroso climbing additive, neither work well with GMposi clutchs. :3gears: Roger
Thank you for the response. So, I should buy 80W-90 and add the GM additive. Here's the thing, the 80W-90 GL-5 says it's also for limited slip? Also, I heard the one with GL-5 is bad for yellow metals like brass etc, do I have any yellow metal in my differential? Tks.
Will need to buy the GM posi additive... about $7 at the dealer. The 80-90 GL5 may read that it works for limited slips, but it does not work well at all in the clutch type GM posi's. Roger
Amsoil I have a 12 Bolt from a Monte Carlo and 3:31 gears from a 70 Chevelle in my 70 GS. I used Synthetic Amsoil 75w90 gear lube with a bottle of Champion limited slip gear lube. Works perfect! Mike
