A harsh gear change is normally caused by a stuck valve in the Valve body, A worn piston, Shift Valves and solenoids. Usually reconditioning the valve body will solve the problem, but once again if the vehicle is driven with this problem the harsh gear change can damage the mechanical parts in the gearbox. Once the valve body has been reconditioned it needs to be re-adapted with a special diagnostic tool which Sparklight Gearboxes are capable to do on almost all vehicle brands.