The winch pulling capacity depends of how many layers of cable is on the drum. The closer to the bottom layer the more pulling power. Make sure that the cable is pulling  under the drum, -never on top. If the winch backs off during winching with a rattling sound the dog clutch # 27 is slipping and need to be replaced, include new bolts # 25,25. The spring # 9 that holds the clutch engaged should be replaced together with new o-rings # 5 and 6. For part numbers click here.