I need to refill the fluid in my 1979 F150 transmission which is a four-speed manual. I was wondering if I can use automatic transmission fluid (ATF) in the C6 transmission. Could I also use ATF in the transfer case? Thanks

 

Type F in the C6 though other ones may work . 50W or 80-90 in the manual transmission. what transfer case do you have ?

 

All I know is that the transfer case is a 4 wheel drive

 

four speed manual and c6 are two different transmissions. If it’s a 4speed (np435 or T18) use gear oil. If it’s a C6 then ATF.

Either way the TC if it is original would likely use gear oil. If it is a newer aluminum TC (be1356) then ATF

 

DO YOU HAVE A GAS PEDAL, A BRAKE PEDAL, THEN ANOTHER PEDAL ON THE LEFT LIKE A CLUTCH USED TO SHIFT? YES/NO

DO YOU HAVE A GAS PEDAL, A BRAKE PEDAL THEN A BLANK AREA BETWEEN BRAKE AND PARK BRAKE PEDAL? YES/NO

if you answered yes to question 1) then you probably have a manual shift with a 3 on the steering column selector or even more probable a bug iron rod protruding from the floor near the forward middle of the cab. this variation would be a manual shift, and should be filled with the proper fluid for that gear box type, probably being a gear oil like 75w-140, sae 90, 80w-90, 85w-140 and also must be serviced from under the vehicle.

If you answered yes to question 2) hopefully this means you answered no to number one and that might mean you have a gear selector mounted on the steering column as well as an indicator of P-R-N-D-2-1 unless converted to aftermarket floorshifter for racing, or some other nonsense. This would be an automatic likely calling for a quantity of ATF maybe type f maybe mercon maybe something else. This would be serviced by draining underneath and refill would be from top in engine compartment.

Transfer case is serviced from underneath and is very probable original and if so calls for a 80w-90.