I recently purchased a used Troy Bilt ZTR. The right wheel drives OK in forward (in fact it goes faster than the left side). It jerks in reverse or does not drive at all unless the left side is driving (either fwd or rev). Even then, it goes slower than the left side. This makes little sense since the only connection between the two transmissions is the belt. I have checked the linkage and added some fluid. The belt is in good condition and is properly situated on the pulleys. The mower is model 17AA5ABP766 RZT50 and has 130 hours on it.