a hydraulic tool for assembling and disassembling components , such as gears , bearings , etc . of a shaft , is capable of performing an external - pulling or an internal - pulling operation as desired for an object to be assembled or disassembled . the hydraulic tool includes an oil pressure assembly having a hand - operated pump , an oil storage member , a control valve , an oil pressure tank , a set of external pulling type clamping jaws , internal pulling type clamping jaws , and a bolt for assembling purpose . the hydraulic tool has high mobility and portability , is capable of performing assembling or disassembling operations at any angle and position , and is considerably enhanced in applicability .