might ck for slipped/missing axle to wheel key..

Look for the vent - looks like a piece of garden hose on top toward the rear of the transmission. Clean around it, pull the hose out, stick a pencil/wooden dowel to measure level of oil. My understanding is that they take 20-50W oil. I would add until it is 3/4" from top. -- That is what I did to my MTD Yardmachine, I am assuming that your system will be very similar. It worked like magic on mine!

When you check the level, look at the color of the oil on the measuring stick - if it looks like it is toasted you may want to suck it out and replace it. If you search this forum there should be many theads that address this.

Good luck!