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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.
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.
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?
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.
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.
Last edited by fastimes; Dec 16, 2018 at 05:30 PM.
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.
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).
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Originally Posted by 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.
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
I did exactly the same thing after rebuilding my diff...
Originally Posted by Crimson Thunder
I also used what Gary recommended. Lucas 85/140 with a bottle of GM fluid. No problems at all.
Originally Posted by 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).
diff fluid c3 1972
