Servicing Vetus Hydraulic Steering Rams
Push the cylinder rod side to side and feel it move more than it should — that’s the seals telling you they’re done.
Paikea’s steering rams had been leaking hydraulic oil since we got the boat, and once the play in the rod confirmed it, there wasn’t much point putting off the strip-down any longer. Hard, collapsed piston seals don’t clamp properly, and once they’ve lost their shape, oil finds a way past them no matter how many times you top up the reservoir.
Getting the end caps off
The first surprise with these Vetus rams is that the end caps aren’t threaded on — they’re held by a stainless steel retaining wire that sits in a matched groove between the cylinder and the cap. A dedicated C-spanner engages a small drilled hole to rotate the cap enough to work the wire free, then the whole end simply pulls straight off once the wire’s out. It’s a neat design once you understand it, and worth knowing before you go anywhere near it with a wrench looking for threads that aren’t there.
Two seal types, two different jobs
Inside, there are two kinds of seals doing different work. The piston carries bucket seals — directional lip seals that control oil moving on either side of the piston as pressure is applied, pushing the ram in or out depending on which port the oil enters. The end caps carry a lip seal around the rod itself, plus an O-ring sealing the cap to the cylinder body.
The lip seals only work one way. Each has a defined lip, and that lip has to face the direction the oil pressure comes from — pressure pushes up under the lip and forces it harder against the sealing surface, which is what creates the seal in the first place. Fit one backwards and it simply won’t seal, no matter how new it is. Before removing any old seal, take a photo or make a note of which way the lip faces. That’s the single easiest way to save yourself from putting the new one in wrong.
Handling the seals without wrecking them
The bearing surfaces inside the cylinder — the polished sections the rod and piston actually ride on — have to stay untouched. Any score, nick, or bruise there compromises how the ram performs under load, seals or no seals. When levering old seals out, the trick is picking the side to dig into carefully, working from the side that’s less critical to the finished seal surface rather than gouging wherever’s convenient.
Fitting new seals demands the same care in reverse. Every seal goes on with lubrication — a petroleum-based grease if you have it, hydraulic oil in a pinch — because a dry lip seal dragged over a sharp machined edge or a threaded shoulder can shred before it ever does its job. Once torn, that’s a bin job, not a wipe-and-refit. Engaging the seal at one point first, then gently rolling it up and over the radiused edges rather than forcing it straight on, is what keeps a new seal intact through installation.
Putting it back together
With new lip seals and O-rings fitted throughout — piston, both end caps — the rod goes back in, the retaining wire threads back into its groove, and the hose fittings go back on. From there it’s a case of bleeding the system and taking the boat out to confirm the steering feels right.
Thirty-year-old hydraulic rams don’t need replacing just because they’re leaking. Most of the time, they need exactly this — new seals, the right way round, fitted with the same care that put the boat together in the first place.