Is ACDelco 10-4033 transmission and transfer case fluid suitable for a SM420 transmission built in "I"1355. Sept13, 1955. It does have brass synchros.
I have seen it listed as 75W80 and also 75W90. It seems thinner when poured at 60 degrees F. I have seen it listed as mineral oil. I am not sure if it is GL-4 or GL-5 altho it has been alluded to being GL-4. And it is reddish in color.

It appears that the old Dexron III is listed as GL-3 even tho I have not seen it for sale - I do not know if this is true.
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Last edited by 42465967; 02/12/2022 3:47 PM. Reason: words
1959 GMC 100 Fleet
Follow in the DITY