Hey Barbara. I had one come to me that was doing the same thing, Breaking Belts. I found that someone had hit something and Caused the Drive pulley to become"Un-True". meaning it had one side wider than the other. made the belt really vibrate instead of running smooth. you couldn't tell it be riding it, but when you look at it run, you could see "Slack then tight". I replaced the pulley and Solved the problem, been 3-4 years now on the same belt. just looking close at the pulley, you could see wear more on one section than the other. Maybe "Paint" the pulley black, let dry, use it and see if you can see more wear on one side than the other, or by hand, turn the pulleys and see if the belt "sits Higher" in the grove or the Valley 1/8 inch is a LOT at high speed. Hope this helps. (Texas Here)