Hydraulic systems function by transferring force applied at one end of the system through the compression of an oil-based fluid. The system's hydraulic pump functions by using the weight of a lager amount of fluid to compress a smaller amount of fluid through a hose to operate pistons that operate an apparatus such as a tractor's plough or tiller. Over time the bearing and seals in the hydraulic pump will wear out, requiring you to change the tractor's hydraulic pump.
Lower all hydraulic powered accessories to the ground, using their control levers. Disconnect the tractor's negative battery cable with a wrench.
Place the drain pan under the hydraulic fluid reservoir and remove the drain plug from the reservoir with a socket wrench. Replace the drain plug after the fluid has drained. Move the drain pan under the hydraulic pump. Open the bleeder valve on the hydraulic pump with a wrench to relieve any pressure in the pump.
Loosen the tension bolt on the generator's tensioner pulley with a wrench. Wiggle the tensioner pulley with your hands until the tractor's drive belt becomes slack.
Disconnect the inlet and outlet hydraulic hoses from the hydraulic pump with a box end wrench and drain any remaining fluid into the drain pan. Remove the hydraulic pump's mounting bolts with a wrench and remove the pump from the tractor.
Attach the new hydraulic pump to the tractor with the mounting bolts. Screw the fittings of the inlet and outlet hydraulic hoses into the new pump with your fingers and the tighten with a wrench. Open the bleeder valve on the new pump with a wrench.
Align the tractor's drive belt on the pulley of the new hydraulic pump. Place the drive belt into the generator's tensioner pulley and apply pressure against the generator's housing, using the pipe to gain leverage. Tighten the tension bolt on the generator's tensioner pulley with a wrench.
Fill the hydraulic fluid reservoir with fresh fluid. Reconnect the negative battery cable and start the tractor's engine. Operate all the controls for all hydraulic accessories on the tractor through their full range, several times, until a steady stream of fluid starts to come out of the bleeder valve. Close the bleeder valve and top of the fluid reservoir.