Combines f2 belt flop on pivot shaft drive

Sounds like the belt is being pinched by the sheaves. This will happen when you put a new belt on adjustable sheaves. look at the side of the belt to see if the top or bottom of the belt sides are wearing. The sheaves will wear more in the areas you use the most (cylinder rpm). Most of time you will have to replace the sheaves when you put on a new belt. You might luck out and will only have to rebuild the adjustable sheave by putting in new bearings.

Years ago my grandfather bought an f and we were new to gleaner.we had the same probelem as you ...i think....when we bought it the belt on the shaft and the other pulley was tilted slightly. we put several belts on it and still it flopped around. we later for the bearings were gone. we took it to our gleaner dealer and got this fixed but then traded and then payed big bucks for a 1660 international.but now back to GlEANER..better machines!!