Right after I got my Bolen's G16XT the clutch/brake pedal would constantly jump about 1/4". Took a lot of investigating but finally found it. The pulley on the right-angle gear box was one of the made-up ones with the hub welded to the pulley. Only in this case they did not get the pulley centered on the hub, which threw it out of round in turn causing the jump in the belt and everything around it. Replaced the pulley and has been smooth as could want it ever since. My gear drive tiller tractor.