1949 Dodge 1 1/2 ton transmission fluid requirment

[Ken1955]

I am trying to find out what type/ weight oil goes into my standard (on the floor) transmission. I have read and been told everything from 10w oil to 80/90 rear end fluid. Would appreciate any help.

1949 Dodge 1 1/2 ton 5 window truck. Flathead 6 with dually rear end. Used to have dump bed.

[Dodgeb4ya]

Any 85/90 weight oil... no brass or syncro's in your 4 speed spur gear trans.

[Ken1955]

Thanks a lot.

[9 foot box]

For my fluid changes I've been staying with GL-1. Thats what was made at the time, for all cars or trucks. The issue being that oil labeled EP has  additives that are harmful to yellow metal.