Hydraulics have been installed on cars since the mid 1950s. Every hydraulic system is different, but they all use a cylinder to lift the suspension of the vehicle up in the air. The seals on these cylinders are crucial, because if they start to leak, they don't hold pressure. If they don't hold pressure, they won't lift the vehicle. In this case, the project vehicle is a 2001 Ford Focus wagon and the rear cylinders, but the process is similar for other vehicles as well.
Lift up the rear of the vehicle using the jack and secure it on jack stands. Make sure the vehicle is solidly set on the jack stands before crawling underneath it. Unbolt the rear tires from the suspension using the tire iron and set them to the side. Place a drain pan underneath the hydraulic cylinder.
Locate the collar at the base of the cylinder, which sticks out from the widest part of the cylinder and is approximately 2 inches high. Unscrew this collar using your hands.
Unbolt the bottom of the cylinder from the lower control arm using the 3/8-inch ratchet and socket. Pull the cylinder shaft out of the cylinder using your hands to expose the top of the cylinder piston and the seals.
Remove each cylinder seal from the top of the cylinder using the flathead screwdriver, taking note of which type of seal goes where. There are white Teflon split seals, poly-pack seals and traditional round seals. Just note which shape goes where and you'll be OK.
Install the Teflon seals from the replacement seal kit by pushing the seal toward itself at the split in the seal, then spread it apart and around the cylinder. Use the flathead screwdriver to install the remaining poly-pack and/or rubber seals on the piston.
Push the cylinder piston back into the cylinder and tighten the collar back onto the base using your hands. Bolt the bottom of the cylinder to the lower control arm using the 3/8-inch ratchet and socket. Reinstall the rear tires using the tire iron and lower the vehicle off of the jack stands.