No, they aren’t the same things. There are definitely a few differences between Harley-Davidson Transmission Fluid and Primary Fluid. Most of the time, transmission fluids will have higher viscosity. Viscosity is essentially the speed at which oil flows. Transmission fluids will help in reducing transmission gear noise while also helping in enabling easy shifting. On the other hand, most Primary Fluid options will be a lot thicker. They focus on offering much better stability and great performance.