Drop the rear end cover plate and inspect the cross pin that holds the spider gears in place. If the lock bolt for that pin breaks or backs out, the pin can slide out and lock up against the rear end housing. You'll be able to get a little movement, but considerably less than half a turn of the rear wheels.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!