It's the blade elevation control
I can't remember at which point the belt becomes the tightest, fully up or fully lower, but find that out. It should mean the motor is pivoted up closest to the rear of the table. Adjust the motor mount on the sliding rods so the belt is not "super" tight, just tight. Then lower the blade and see if it gets sloppy at the full lower position, if so..... You have the wrong size belt. If I remember it takes either a 4L42 or 4L43 belt. My saw was a 1960's version.
Theoretically you want the belt the tightest at fully up because that's when you need the maximum power from the motor.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 02-09-2013 at 04:09 PM.