SeaStar / Teleflex
Steering Cylinder Repair
& Rebuild
Mercury Hydraulics repairs and rebuilds all SeaStar and Teleflex HC-series hydraulic steering cylinders. Full machine shop — we re-chrome rods and re-hone bores, not just swap seals. Ships nationwide.
The Most Common Marine Steering Cylinder — And Why It Fails
SeaStar and Teleflex hydraulic steering cylinders are installed on more recreational boats than any other brand. Originally manufactured by Teleflex Marine, the HC-series cylinder line was acquired by SeaStar Solutions and is now sold under the Dometic SeaStar brand. Regardless of the nameplate on the cylinder, the internal geometry, seal dimensions, and failure modes are consistent across the entire HC-series product line.
The most common failure mode is seal deterioration — the piston seal, rod seal, and wiper seal degrade over time from UV exposure, heat cycling, and contaminated hydraulic fluid. When the seals fail, hydraulic fluid leaks from the cylinder body or around the rod, steering becomes hard or spongy, and the engine may drift off center when the wheel is released.
Mercury Hydraulics repairs and rebuilds all HC-series cylinders — HC5322, HC5323, HC5340, HC5345, HC5347, HC5348, HC5370, HC5380, and all variants. Unlike shops that only swap seals, we are a full machine shop: we re-chrome scored rods and re-hone worn bores, which means we can save cylinders that other shops declare unrepairable.
HC-Series Models We Service
All SeaStar and Teleflex HC-series hydraulic steering cylinders
| Model | Application | Mount Type | Engine Range | Notes |
|---|---|---|---|---|
| HC5322-3 | Inboard / stern drive, standard | Rear mount | Single/twin to 300HP | Most common inboard cylinder |
| HC5323-3 | Inboard / stern drive, heavy duty | Rear mount | Single/twin to 400HP | Heavier wall, larger bore |
| HC5340-3 | Front mount outboard (older) | Front mount | Single to 150HP | Discontinued; rebuild only |
| HC5345-3 | Front mount outboard, standard | Front mount | Single/twin/triple to 350HP | Current standard outboard cylinder |
| HC5347-3 | Front mount outboard, heavy duty | Front mount | Twin/triple to 600HP | Larger displacement, heavier rod |
| HC5348 | Front mount, triple outboard | Front mount | Triple to 900HP | High-performance applications |
| HC5370 | Side mount cylinder | Side mount | Varies | Trawlers, larger vessels |
| HC5380 | Big boat / inboard, heavy duty | Rear mount | Large inboard | Commercial and large recreational |
Don't see your model? Call us at (321) 312-0689 — we service all HC-series variants including older Teleflex-branded cylinders.
Common Failure Modes
Diagnose your SeaStar or Teleflex cylinder before shipping
Seal Failure
Symptom: Hydraulic fluid leaking from cylinder body or around the rod
Cause: Age and UV exposure degrade the internal piston seal, rod seal, and O-rings. The most common failure mode in all HC-series cylinders. Accelerated by contaminated fluid or infrequent fluid changes.
Fix: Full seal replacement — piston seal, rod seal, wiper seal, and all O-rings replaced as a set. Bore inspection included.
Rod Scoring
Symptom: Visible scratches or grooves on the cylinder rod; accelerated seal wear
Cause: Abrasive contamination in the hydraulic fluid, corrosion from saltwater exposure, or physical impact. Scored rods destroy new seals within weeks if not addressed.
Fix: Rod re-chroming or rod replacement. Mercury Hydraulics has full machine shop capability to re-chrome and grind rods to OEM tolerances.
Hard / Stiff Steering
Symptom: Wheel requires excessive force; steering feels tight or locked
Cause: Internal seal bypass reducing pump pressure, air in the system, or a seized support bracket binding the cylinder.
Fix: Seal replacement and system bleed. If the support bracket is seized, it may require cutting and replacement.
Spongy / Mushy Steering
Symptom: Wheel turns but helm feels soft; boat response is delayed
Cause: Air in the hydraulic system, most often introduced after a seal failure allowed fluid loss or during a fluid change.
Fix: System bleed procedure. If air re-enters quickly, a seal failure is allowing fluid loss and must be addressed.
Engine Drifts Off Center
Symptom: Engine slowly returns to center or drifts to one side when wheel is released
Cause: Internal bypass in the cylinder — the piston seal is no longer holding pressure in one direction, allowing the engine to drift.
Fix: Piston seal replacement. If the bore is worn, re-honing and oversized seals may be required.
Bent or Damaged Rod
Symptom: Visible bend in the cylinder rod; steering binds at certain angles
Cause: Impact damage from running aground, hitting a submerged object, or overtorquing the steering system.
Fix: Rod straightening (if minor) or rod replacement. Mercury Hydraulics can fabricate replacement rods to OEM dimensions.
Full Machine Shop vs. Seal-Swap Service
Most marine repair shops can only replace seals. Mercury Hydraulics can do everything.
Seal Replacement
All piston seals, rod seals, wiper seals, and O-rings replaced with new components. Standard on every rebuild.
Bore Re-Honing
Worn or scored cylinder bores are re-honed to restore the correct surface finish and diameter for proper seal seating.
Rod Re-Chroming
Scored or corroded cylinder rods are re-chromed and ground to OEM tolerances. Eliminates the root cause of accelerated seal wear.
Rod Fabrication
Bent or damaged rods beyond re-chroming are fabricated from scratch to OEM dimensions using our CNC machine shop.
Pressure Testing
Every rebuilt cylinder is pressure-tested to rated working pressure before return. No exceptions.
Bracket & Hardware
Support brackets, mounting hardware, and end fittings are inspected and replaced if corroded or damaged.
The Rebuild Process
Ship your cylinder to us — we handle the rest
Disconnect & Remove
Disconnect hydraulic lines and cap immediately to prevent contamination. Remove the cylinder from the engine bracket. Drain residual fluid before shipping.
Pack & Ship
Wrap the cylinder in a sealed bag to contain residual oil. Pack securely with padding. Ship to Mercury Hydraulics at 7610 Coral Dr, Melbourne FL 32904 with your contact info and symptom description.
Inspection
Our technicians fully disassemble the cylinder, measure bore diameter, inspect rod surface condition, and evaluate all sealing surfaces. We contact you for approval before proceeding if additional work is needed.
Machine Work (if needed)
Scored rods are re-chromed and ground to OEM tolerances. Worn bores are re-honed. This is the step that separates a full machine shop from a seal-swap service.
Rebuild & Test
All seals, O-rings, and wiper seals are replaced with new components. The rebuilt cylinder is pressure-tested to rated working pressure before return.
Return Ship
The rebuilt cylinder ships back within 2–4 business days of receipt with a 6-month limited warranty. Rush turnaround available — call to discuss.
Rebuild vs. Replace Cost Comparison
Based on HC5345-3 (most common outboard cylinder)
| Cost Item | Rebuild (Mercury Hydraulics) | New OEM Replacement |
|---|---|---|
| Cylinder rebuild / unit cost | $195–$295 | $350–$500 (HC5345-3 OEM) |
| Rod re-chroming (if needed) | +$75–$150 | Included (new unit) |
| Bore re-honing (if needed) | +$50–$100 | Included (new unit) |
| Installation labor | $0 (reinstall same bracket) | $100–$200 (new bracket/hardware) |
| Shipping (round trip) | $30–$60 | $0 (local purchase) |
| Total estimate | $195–$505 | $450–$700 |
| Warranty | 6 months (Mercury) | 2 years (SeaStar OEM) |
| Turnaround | 2–4 business days | In stock or 1–2 weeks |
Rebuilding makes the most sense when the cylinder body is structurally sound and the failure is limited to seals or rod surface condition. Replacement is the right call when the cylinder body is cracked, the rod is severely bent, or the mounting bracket is corroded beyond repair. When in doubt, call us — we will give you an honest assessment.
Frequently Asked Questions
Can SeaStar and Teleflex steering cylinders be rebuilt?
Yes. All SeaStar and Teleflex HC-series hydraulic steering cylinders are rebuildable. Mercury Hydraulics replaces all seals and O-rings, inspects and re-hones the bore if needed, re-chromes or replaces scored rods, and pressure-tests the rebuilt unit before return.
What is the difference between SeaStar and Teleflex cylinders?
Teleflex Marine originally manufactured the HC-series cylinder line. SeaStar Solutions acquired Teleflex's marine division, and Dometic later acquired SeaStar. The cylinders sold under all three brands are functionally identical — same dimensions, same seal kits, same repair procedures. If your cylinder is stamped Teleflex, SeaStar, or Dometic SeaStar, we service it.
My HC5345-3 cylinder is leaking — is it worth rebuilding?
Almost certainly yes. A leaking HC5345-3 is almost always a seal failure, which is a straightforward rebuild at $195–$295. A new OEM HC5345-3 costs $350–$500 plus installation. Unless the rod is severely bent or the body is cracked, rebuilding is the economical choice.
How do I know if my cylinder rod needs re-chroming?
Run your fingernail along the rod surface. If you can feel grooves or pitting, the rod is scored and will destroy new seals within weeks if not addressed. Visible rust streaks or corrosion pitting are also indicators. Mercury Hydraulics inspects every rod during teardown and will advise you before proceeding.
How long does a SeaStar cylinder rebuild take?
Most HC-series cylinder rebuilds are completed and shipped within 2–4 business days of receipt. If machine work (re-chroming or re-honing) is required, add 1–2 business days. Rush turnaround is available — call (321) 312-0689 to discuss your timeline.
Does Mercury Hydraulics also repair SeaStar helm pumps?
Yes. Mercury Hydraulics repairs and rebuilds SeaStar and Teleflex hydraulic helm pumps in addition to cylinders. If both your helm pump and cylinder are failing, we can rebuild both units together for a complete system restoration.
Ready to Ship Your Cylinder?
Call or email us first — we can confirm your model, give you a firm quote, and tell you whether machine work will be needed before you pull the cylinder off your engine.