Small Engines (Lawn Mowers, etc.): Vibration when the mower is in gear, spindle bearings, lawn chief

Question
I have a 1998 Lawn Chief riding lawn mower.  The model # is 13AN678G022843706.  When the mower is in gear it vibrates heavily.  What can I do to fix this??

Answer
Unbalanced or bad blades?  Blade spindle bearings wore out?  Idler pulley wore out?  Bad belt?


Use the site below to locate your Owner's Manual that tells you how to check/replace the blades.

http://manuals.mtdproducts.com/mtd/public/list.jsp

Let me know what you find on the deck.
Eric