Yes, You can. But quality of the mixture will be equal to the quality of the GL4 gear oil.
The best gear oil for a Case Vac tractor is Engen Gearlube EP 85w140.
vauhall gear oil gl4 NOT gl5
85W140 Gear oil on a manual transmission.
one gallon of 85w140 equals 7.53 lb/gallon 120/7.53=15.936 gallons
80w90 GL3 or GL4 gear oil.DO NOT USE GL5 Gear oil as this will eat away at the brass syncronizers in the transmission.
gL4/gL5 sae 75w90 for tranzmision or can use 80w90 for diffs
The Isuzu NPR uses 85W140 gear oil in the differential and you can use chevron starplex 2 grease when greasing the chassis.
About 2.4l of SAE 75W-85 API GL4 - Taken from specs of M32WR gearbox - Nut.
in the fill p;ug just above the drain plug half way up the trans and use gl4 synchromesh
80-90 wt GL-4 gear lube. It needs to be a GL4 rated oil, not GL5 rated.
1986 to 1996 Manual Transmission and Transfer case use API GL4 or GL4 and GL5 80W90 or 75W90. Differentials use API GL-5 SAE 75W-90 or 80W-90 lubricant. Do not put a GL5 gear oil in the transmission unless it says GL4 and GL5. GL5 will attack the syncros.