Well, this might sound pretty novice but I've never encounterd this problem before. I've got a new Cub Cadet Commercial 52" belt drive walk-behind, it's still under warrenty but I'd prefer to get her going on my own. The left drive belt has been pulling itself off the pullies (inward) rather consistantly. Needless to say it's a real hassle to disengage the blades and shut her down frequently to pull the belt back in line. I've tried adjusting the brakes and whatnot to increase tension but with little luck. it has what they call a "Vari-Touch" drive assembly which is a spring-loaded kick down lever to increase traction in wet conditions. Works great for it's intended desisn but it makes handling the mower a real bear, she pulls hard when the levers are in their lowest position. Regardless, it doesn't do a thing for the belt situation. The left belt has far mopre play than the right belt but I just don't see how to tighten it. Any thoughts/advice much appreciated!