how can I fix my front left drive wheel on a Toro self propelled mower ?

I had been cutting weeds{ Tall Weeds} & when I was thruogh, my self prop. mower was really pulling weak. I turned it over to clean out all the weeds rapped around axle & transmission. I tried it again & it was no better. I had another mower years back that needed a new wheel because of worn gears inside. I thought maybe this might be the problem w/ my Toro. I took the wheel off, & realized there was more to this wheel than the wheel from my other mower. anyway, I can't seem to get this wheel back on right. It pulls weaker than ever now. anybody know how to fix this problem. I sure would appreciate some help.