Under certain conditions the gearbox in some Self Propelled - Variable Speed, Series 21 Steel and Alloy mowers are failing with internal parts that are unable to be repaired. (GEARBOX-VAR SP&V782 SYNCHRO 21, part number 567357) <br><br>In the event of a gearbox fail, this kit comes packaged with a full set of instructions and parts to carry out the conversion including a replacement gearbox. (It is not possible to just swap to the replacement gearbox). <br><br>Note: The gearbox ratio is slightly different. This gearbox will increase the forward speed by roughly 20% at the previous settings.