When all else fails read the Manual for the Master Mechanic Model 8575 Three Inch Belt Sander
Auto-Belt Control System
Your sander features an automatic belt control system which keeps the belt running in the center of the pulleys after inital adjustment. The system has been preset at the factory but may require adjustment when belts are changed or an older belt stretches.
Adjusting the Auto-Belt Control System
1) Plug in the cord with the tool OFF.
2) Hold the handle of the sander with one hand and tilt back until the belt is off the work and the sander resting on the bottom heel of the housing.
3) Turn the tool ON by pressing the trigger.
4) For best prformance the belt should be in line with the outer edge of the rear pulley. If the belt deviates more than 1/8 of an inch from the outside of the sander, adjust the belt position by turning the auto-track adjustment screw (On the left side of the Sander), until the belt returns to the proper position.
Should solve your problem.
See the one photo in my album for a scan of the instructions.
Last edited by once in a while; 07-06-2011 at 08:15 PM.