The hydraulic cylinder can take a beating lifting heavy loads day in and day out. Eventually, the seal ring in the piston inside the cylinder can wear out and the cylinder with start leaking hydraulic fluid. You need to replace the seal ring to stop the leak and to get the cylinder to function normally again. If you own an old forklift that has a leaking hydraulic cylinder, here is an overview of how you can replace the seal ring on the cylinder's piston to stop the leak with parts from a place like Crown Equipment.

Remove Hydraulic Hoses

Remove the hydraulic hoses from the cylinder. The hoses are connected to the cylinder using fittings called "quick connects".  You need to pull back on the movable head of the fitting to release it from the cylinder to remove the hydraulic hoses.

Remove Cylinder

The cylinder is connected to the carriage that raises, lowers, and tilts the forks on the forklift and the mast of the forklift by a pin at the top and bottom of the cylinder. You need to remove the pins to take out the cylinder so you can work on it. You can pound the pins out with a hammer and large screwdriver.

Remove Piston

You want to secure the cylinder in a large vise so it doesn't move. Take a large pipe wrench and place it around the cap on the cylinder. Turn the cap counterclockwise to loosen and remove it. Once the cap is off of the cylinder, take a 2-ton come-along and attach it to the end of the piston. A come-along is a tool that you use to pull heavy things. Use the come-along to pull the piston out of the cylinder.

There is a nut you have to remove at the base of the Piston. Remove the nut and slide the piston off of the stem of the cylinder. 

Remove Worn Seal Rings

There is a round dust protector in the opening of the piston and a seal ring inside the piston. Remove the dust protector wand seal ring with a screwdriver. 

Install New Seal Rings

You should take the time to clean the piston before you replace the seal ring. The new seal rings will come in a package you can get at a building and supply store. Push the seal ring into the piston and set it in the place of the worn one. You can then put the new dust protector in the opening of the piston.

Reassemble Cylinder

Put the piston back on the stem and reinsert it into the cylinder. Attach the cylinder back onto the forklift and reconnect the hydraulic hose lines. Operate the forklift to make sure the forks go up and down and tilt forward and back.