I have a John Deere 930m for some reason deck belt now squeals and deck stalls at moderate grass that mower used to walk right through easily. have checked all pulleys and replaced belt and tension arm and spring and nothing seems to help.
Double check the deck drive pulleys to make sure the belt isn't bottoming out in the groove. A worn pulley will allow the belt to set too low in the groove and if the bottom of the belt makes contact with the bottom of the groove won't grip properly and slip.
