Camaro Research Group Discussion > Originality
M21 Correct Oil
miket1:
What Oil did GM install in the M21 Transmission at the factory, was it a GL5 oil, was it a 75w90 .
Thanks
L78 steve:
GL5 is the grade 75w90 is the weight. You will find both on the same container. That is fine for your Muncie.
bcmiller:
I always use the GL4 85w90 from NAPA. StaLube I think is the name.
Do not use GL5.
1968RSZ28:
Any brand-name 75W90 or 80W90 gear lube will work fine - that's what it was designed, developed, and tested with.
Paul
bcmiller:
I disagree. You don't want to use GL5 or any synthetic lube in a Muncie. GL5 is not good for the brass synchros.
I know about 8 years ago crash was recommending Pennzoil 80/90 gear plus which was also GL4 back then. Not sure on that now.
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