Yale transmission not working

I'm helping an older gent around his shop and he asked me to look at an older forklift. It looks to be an early 70's model with a flathead 6 and a combination of clutch and fluid /torque convertor. The problem is that I can't disengage the clutch to shift any gears. I have checked to see that the friction plate is not stuck to the flywheel, the clutch linkage moves freely. I tried adjusting the clutch through the range of adjustment. Am I looking at the fluid coupler now ? Thanks Wayne

Yale transmission not working