• Repacking a Hydraulic Cylinder [A Step-by-Step Guide]

    There are multiple types of hydraulic cylinders but the process for checking and repacking them is generally the same. There are a few telltale signs that your hydraulic cylinder needs to be repacked:

    • Difficulty lifting a load or moving a component (not moving as fast as its supposed to)
    • Implements leaking down faster than normal
    • Cylinder is leaking oil externally – they can leak and still have power

    How to Test a Cylinder 

    Step 1: Fill both sides of cylinder with hydraulic fluid.

    Step 2: Move the cylinder through its full stroke several times to push all of the air out if needed.

    Step 3:  Pressurize cylinder fully extended and check for any leakage

    Step 4:  Retract cylinder and hold, check for any leakage

    Step 5: Internal bypass test-  Begin to retract cylinder and hold with base port line removed and capped, Depending upon type of seal determines acceptable leakage, however generally you will see the cylinder rod actually extend as fluid fills the chamber if the fluid is bypassing the piston seals .


    Hydraulics are an important and expensive part of construction and farming equipment. Here are a few tips to keep in mind while working on the cylinders to prevent costly damage:

    • Make sure your rod is straight
    • Make sure that the inside of the barrel surfaces are showing the proper cross hatching
    • Make sure that there are no scars or gouging
    • Make sure that the chrome plating on the rod is not damaged and if there is a slight nick make sure that there are no raised burrs


    Before you repack you will need to clean off the unit, disconnect any hoses and plug all ports before disconnecting the hydraulic cylinder. Once it has been disconnected you will need to open the ports and drain the hydraulic fluid found in the cylinder.

    Have your tools ready. You will need a seal kit, rubber mallet, screw driver, punch, pliers, spanner wrench, allen wrenches, emery cloth, and a torque wrench.


    1. Release all pressure and remove cylinder from machine.
    2. Clean off dirt that has built up on the cylinder head and end cap
    3. Remove the rod assembly as described in the next step depending upon application.
    4. Take off the external steel wire ring or unscrew the end cap (This may require removal of an allen bolt)
    5. Get your rubber mallet and punch on cylinders with snap rings. Use them to push the head into the cylinder tube until the internal tube groove is completely exposed. This will get the snap ring into position so you can remove it.
    6. Pull the piston rod from the cylinder.
    7. Remove lock nut.
    8. Remove piston.
    9. Check for burrs of gouges on the cylinder rod, piston and bore. If needed remove burrs with emery cloth.
    10. Be sure cylinder rod is straight
    11. Install new seals and replace components as needed. 
      Repack Hydraulic Cylinder
    12. Install cap and seals followed by the piston and seals. Torque lock nut to spec. Repacking a Hydraulic Cylinder
    13. Clamp cylinder body in vise gently.
    14. Lube barrel and all seals to begin assembly.
    15. Insert piston, gland and rod assembly into the cylinder bore.
    16. Tighten cylinder end cap and torque screw or install ring depending upon application.

    Hydraulic Systems Training & Support

    As part of Diesel Laptops' continued commitment to off-highway diagnostics training, we are excited to add our 2 Part Hydraulics Class.

    In the Construction, Agricultural, Industrial, Mining, Vocational industries all use Hydraulic systems.  Learning the basics of these systems can help reduce major equipment failures and loss of revenue due to downed equipment.

    Previous article The Diesel Technician Shortage Explained


    Ivy Baker - February 11, 2021

    This is some really good information about hydraulics. It might be smart for me to look into getting a pressurized cylinder. It does seem like a good idea to get a professional to handle your hydraulic system care. I know that I wouldn’t know how to repair something like that myself.

    Leave a comment

    Comments must be approved before appearing

    * Required fields

    How much is: