Small Engines (Lawn Mowers, etc.): self propelled gear box, self propelled mower, model number

Question
My mother in law has a 6.75 hp 22" briggs engine, craftsman self propelled mower. The belt got chewed up and I replaced it. I am thinking that is not the problem as it still wont't propel. I kept the cover off and watched the pulley as I pushed in the self propel handle. It would spin and stop, then go really slow and stop.

Is it the gear box?

Thanks!!
Jay

Answer
It could be the gear box.  What is the mower model number?  The model number is located on a sticker, about the size of a business card, and the model number format will be something like xxx.xxxxxxx.

Send me the model info so I can look up your gear box.
Eric