The drive pin in the shaft is sheared by why did it break? They don't usually fail unless there is a major transmission problem. Best to take it to an experienced tech if you are not familiar with it, removing the gearbox is somewhat involved.

Originally, I had no drive, but it turned out to be the transmission gears were stripped. I had the transmission rebuilt and the mower ran for about 2 months.....last weekend while mowing, I lost the self propelled again. This time I have no output from the drive shaft. The transmission is ok, but output (not spinning). Is it repairable? Is is worth repairing the shaft?
mahalo,
Joe

Anything including your transmission is repairable. However you or your mechanic needs to look into why you have had two failures in 2 months. You may want to have a different mechanic look at your machine.

If this is the mower then it may have nad a lot more use than you thought when you bought it. http://forums2.gardenweb.com/forums/load/lmower/msg051402419075.html