autoalain

Hi, looked at old threads, just to be sure, can I put in regular
90 weight gear oil, and then just add the gm additive. My parts store
was not sure. Thanks Mike.

leadfoot4

That should work just fine. Just make sure that the gear lube that you purchase, doesn't already have the limited slip lube in it (some do), as too much of the additive will cause the clutches in the differential to slip too much.

fastimes

I have been searching for the same answer, however, I'm not finding any straight 90 weight anywhere.
Are people using the same gear oil in their M20 gearbox and rear diff? 80w90 or 75w90?

Bills17n72

if it was me ,I would just go to the nearest GM dealer and get the right type of gear lube that it calls for!

blue427

acdelco dexron gear oil 75-90 part no#10-4061 (get 2) acdelco limited slip axle lubricant additive part no#10- 4003(get 2) buy it off one of the vendors on the forum.

JoeMinnesota

pws69

Mobil 1 gear oil + GM additive.

TimAT

GM Part Numbers:
88863089 Gear oil (2 Quarts)
88900330 Limited Slip Additive (1 bottle)

fastimes

Anyone have any experience with Lucas 80w90 Gear Oil? It says no limited-slip additive needed, does that mean if used in the differential no GM positraction additive is necessary?




Also considering Driven 80w90 Gear Oil for both my gearbox and differential. Any input is appreciated.

BKarol

When I changed my gear oil, I heeded the advice of the Corvette Forum, Tech Coordinator, Gary Ramadie, and used Lucas 85w/140 and bought the additive.
https://www.corvetteforum.com/forums...post1598005034

stingraymax

I did exactly the same thing after rebuilding my diff...

croaker

Bikespace

I bought Red Line 50305 MT-90 75W90 GL-4 Gear Oil for my 80's manual and both 79 and 80 differentials. I've had no problems, and have enough for several more changes, but were I to do it over again, I'd likely follow Gary (GTR1999)'s advice.

Crimson Thunder

I also used what Gary recommended. Lucas 85/140 with a bottle of GM fluid. No problems at all.

resdoggie

Keep it simple. Royal Purple Max Gear. Additive not required.

fastimes

The argument is a convincing one. The opinion of Gary GTR1999 is appreciated and trusted.
After the holidays, I'll change my Diff oil to Lucas 85w140 with AC Delco 10-4003 additive (some folks say one bottle, some say 2 bottles).

kansas123

Rescue Rogers

I use the Driven GL4 in my Muncie. I rebuilt it last year and just pulled it apart to change the gearing from M21 to M20. No metal residue in the case and it ran smooth as glass all summer in all temps

Big2Bird

^^^this^^^

71 Green 454

I did the same thing, used 2 bottles of additive.