I lost the front wheel drive on my BX1800. Dealer pickup up the tractor. Turns out the pin that holds the front U-joint to the shaft sheered off and the U-joint fell off. Couple of days after the tractor came home I found the U-joint amongs the pine needles I was raking. Dealer has no idea what caused this event, neither do I, just glad the my baby is home and doing well. No cost to me thanks to the warranty, (great dealer too)!
I had the same thing happen on my BX2200 twice. After the first time, I bought some extra roll pins just in case. Good thing I did cause it happened a few months later. There have been a few posts on this problem. I don't think anyone has figured out why this happens, we just punch out the broken pin and tap in a new one. I thought there might be a little slop or play in the splines, and this causes the pin to be under stress, which eventualy causes it to break. Just my opinion, I could be wrong.