: Correct Gear Oil

08-26-11, 07:04 PM
The level of oil in the differential appeared to be about 1" low and a friend of mine suggested filling it up with 75-W-140 all-synthetic gear oil. We put some 5 OZ of that and it was still low, so he topped it up with a couple of OZ of 80W-90 synthetic. Later he noticed th edifferential is limited slip and believed it should have taken a special oil.

The question. What oil is supposed to be used? I do not have the manual with me unfortunately.

08-26-11, 08:07 PM
Your Fleet isn't limited slip unless you (or someone else) installed it. G80 (ltd slip) wasn't an option on Fleetwood because it has traction control. It should be filled to the bottom of the fill hole with 80w90. If you did install a clutch or cone posi (Eaton or Auburn), you would put in one bottle of GM posi additive, then fill the rest of the way with the 80w90.

08-26-11, 11:10 PM
Thank you, jayoldschool. I guess a few ozs of 75w-140 instead of 80w-90 are not going to hurt the differential. I am sure the differential is stock.