So what is the consensus as to what primary and transmission fluid I should use on my new to old 78 FXE with a 1340? Jim

 

If it is a stock FXE with the oil return primary it is the same as the engine oil. The primary recirculates the oil back to the motor. If it is an isolated primary, some use ATF so they can see if it is leaking primary fluid. Thats the main problem with the isolated primary, if the level gets low you cook your chain and adjuster shoe in a short distance. In 1978 Harley still recommended the same oil in the transmission as the motor. Later they came out with a bulletin saying they recommended their brand of transmission lube. Basically gear oil. I've used both and see no difference. I've got two bikes running 70 wt motoroil and two running gear oil. The main thing is to keep the level up.

 

Thank you very much for your expert opinion!! Jim