• SeaStar Steering Cylinder Rebuild (Teleflex)

    So you noticed an oily film in your bilge or maybe the steering began to behave in a strange manner. Upon further inspection you have determined the steering cylinder is the guilty culprit. If the cylinder is not the victim of corrosion then it may be possible to rebuild it. Rebuilding a steering cylinder does not demand a lot of technical expertise. However, it does require patience and a cautious approach to avoid scarring or scratching some important parts.


    Click here to download the SeaStar Installation Guide.

    The steering cylinder that I am rebuilding in this example is an older SeaStar unit manufactured in 1986.

    The first step is to get the part number off the label on the cylinder. If the part number is no longer legible a call to Teleflex can usually help you identify the cylinder. At that point prepare to order the correct rebuild kit. The prices on the rebuild kits will vary widely since some of them contain a specialized wrench that is used to remove the end caps of the cylinder, other cylinders require a spanner wrench available at Graingers or similar supply stores. Some of the rebuild kits also come with new end caps for the cylinder, so take you time to ensure you order exactly what you need.

    I recommend waiting until you get all of the parts and tools together prior to disassembling the cylinder. That way the sequence of events and location of parts will stay fresh in your mind.

    The following picture shows the steering cylinder before removal. To remove it you will disconnect both hydraulic lines from the bleeder fittings on the cylinder. Make sure you have a small bucket to catch the remaining fluid along with several absorbent rags. At this point don't try to save the hydraulic fluid, it is likely to be contaminated and could be the source of failure.

    Attachment 563

    Next note the orientation of the bleeder fittings,note the angle and the tilt. This is an important step to ensure that they are oriented in the same manner after you complete the rebuild so the air can be bled out of the system. Now remove the bolts from the rudder arm (1 bolt) and from the cylinder trunion assembly (4 bolts). As you remove the bolts from the trunion assembly pay attention to how the cylinder fits in the trunion to make it easier when it comes time to re-install. In most cases it is not necessary to remove the trunion foot, once the 4 bolts are removed the trunion assembly will separate into halves and the cylinder will slide out.

    Once you have the cylinder removed from the boat move it to a clean workplace for disassembly. This cylinder is known as a single-end cylinder since only one end connects to the steering tiller. This is the starboard end of the cylinder.

    Attachment 574

    This view shows the port end of the cylinder. This is the end that mounts in the trunion assembly.

    Attachment 573

    Now remove the hydraulic tee fittings from the cylinder (remember to note the orientation). The following picture shows the Tee fittings removed.

    Attachment 569

    Now it is time to remove the endcaps. Using a bench vise makes the next step easier but do not clamp the cylinder too tightly or you can damage it. Both the endcaps and the inside cylinder walls have a slot milled into them. The endcap is held into the cylinder by a flexible locking wire that functions like a cotter key (it fills the slots in both the endcap and cylinder to prevent the endcap from sliding out).

    Attachment 570

    To remove the wire, hold the cylinder and using the spanner wrench or specialty tool turn the endcap. As you turn the endcap the locking wire should come into view sitting in the slot. Use a small screwdriver and lift the end of the wire up as you continue to turn the endcap. In this picture I am using vice-grips to hold the cylinder. I do not recommend this since you can ruin the steering cylinder if you are not careful.

    Attachment 571

    In the next picture you can clearly see the groove for the locking wire with the wire removed.

    Attachment 572

    Now the endcap should slide out of the cylinder and allowing the piston rod to be removed as well as shown in the following picture.

    Attachment 575

    Next remove the endcap from the other end of the cylinder. At this point you can see four of the six seals you will need to replace.

    Attachment 576

    The other two seals are hidden on the inside of the endcaps. These are normally the first ones to start leaking since they see the most wear.

    Attachment 577

    You will have to unscrew the Rod End Ball Joint so you can slide the remaining endcap off the piston rod to gain access to one of the seals.

    Attachment 578

    Once this is done it is time to replace the inner seals (one per endcap). Use extreme care removing these seals and do not scratch or scar the piston rod or the inner walls of the endcap. A wooden toothpick works well for this task.

    Attachment 579

    Now make sure the exterior and interior of the endcap are clean before installing the new seals. Lubricate the seals with hydraulic oil prior to installing them. Slip the outer seal over the endcap into position. Using a blunt toothpick insert the inner seal into position.

    Note the orientation of the seals on the piston prior to removing them. They are cupped or tapered and should be oriented with the wider diameter facing away from each other.

    Attachment 580

    Remove the old seals from the piston. Clean the piston and ensure the piston rod is clean showing no signs of nicks, scratches or rust. Lubricate and install the new tapered seals in the correct orientation.

    Now re-install the Piston Rod into the endcap using care not to dislodge the new interior seal. Ensure the endcap is oriented correctly on the piston rod (seal end toward the piston) then screw on the Rod End Ball Joint.

    Attachment 583

    Next clean and inspect the inside of the hydraulic cylinder. Once that is done it is time to begin putting it all back together.

    Install the endcap into the hydraulic cylinder and align the threaded hole for the Bleeder Tee. continue to rotate the endcap toward you until the threads for the Bleeder Tee are just barely visible (almost out of sight). Now insert the end of the new locking wire into the grooved slot and feed the wire as you twist the endcap toward you.

    Attachment 581

    This is what it should look like as you twist the endcap and feed the locking wire.

    Attachment 582

    Continue to rotate the endcap until the threaded hole for the Bleeder Tee is aligned with the hole in the cylinder. The locking wire should now be fully retracted into the cylinder and not block the threaded hole for the Bleeder Tee.

    Now slide the trunion mount endcap into the other end of the cylinder being careful to guide the piston rod through the interior seal. Install the locking wire using the same procedure mentioned above.

    Once both endcaps are secure install both bleeder tees into the threaded holes in the cylinder. Remember to align them to match their previous positions. You can use a teflon based thread sealer if necessary but never use thread tape. Once both bleeder tees are in place, the cylinder is ready to be re-installed.

    Bleeding instructions will come with the rebuild kit. You can build your own bleed assembly by purchasing a quick connect pneumatic air hose fitting which fits perfectly in the threaded fill port on top of the reservoir. A piece of clear hose and the top off of a Lucas Oil Stabilizer bottle fits on the SeaStar bottle.

    Attachment 592


    Comments 2 Comments
    1. outremer's Avatar
      outremer -
      Thanks a lot Tim, you saved my day.
      I used your article on the SeaStar steering cylinder for rebuilding my two Vetus cylinders. (my boat is a catamaran, so two rudders).
      I did not have a clue how to open the cylinders until I found your article, very well written and illustrated.
    1. TimG's Avatar
      TimG -
      Thank you, glad it helped, that is what we are all about!
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