Small Engines (Lawn Mowers, etc.): DRIVE WHEELS LOCK UP WHEN ENGINE OFF, drive pulley, drive wheels

Question
I have a Ariens rear wheel drive self propelled lawnmower.  It is model #911516.  I bought it in 2002.  It has been a good lawnmower.  The spring-loaded pulley idler arm that puts tension on the belt froze up.  I took it apart, lubed it up and changed the rusty washers.  It works great now.  However, now I am having a problem where the drive wheels are locking up and you cannot push the mower when engine off.  It works great otherwise.  If you pick up the mower off of the ground, the rear wheels turn easy one at a time but when turning one wheel forward, the other turns backward.  When you try to turn both wheels forward, they lock up completely.  I checked the vertical wheel that touches the horizontal wheel that is run by the belt.  They are not making contact and the drive wheels still lock up.  I am mechanically inclined, although I don't know all of the parts names.  My Dad was a mechanic and I learned a lot from him but I cannot figure out why the wheels are locking up like this.  I also adjusted the cable that lowers the vertical wheel against the horizontal wheel and no other problems.  The mower cuts grass and works fine when engine is running and self-propelling.  Thanks, Tim.

Answer
TIM
Sounds like the belt that drives the wheels are locked up when the engine is off.I would check the drive pulley and see if it can be moved while the mower is off. The bellt is forcing the drive to move only when the mower is on I would check to make sure it is not stuck. This may have to be replaced. Sometimes lubricating doesn't work.

Thanks