HELP!! Jeanneau NC9 (2019) – Persistent Steering Drift Issue (Volvo Penta D4-260, Sterndrive)

[kljay24]

I’m posting this to see if anyone else has experienced something similar, as I’ve now gone through an extensive (and expensive) diagnostic and replacement process without resolving the issue.

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Fault Description​

• Boat: Jeanneau NC9 (2019)
• Engine: Volvo Penta D4-260 (single engine, sterndrive)
• Steering: Hydraulic power-assisted system

Symptoms:​

• Steering drifts slowly to port or starboard
• Drift often follows the last direction of helm input
• Occurs at idle and higher RPM (e.g. 1500 rpm)
• Occurs in neutral (not in gear)
• Steering holds perfectly when engine is OFF
• Steering wheel does NOT move when drift occurs
• Previously observed hydraulic oil temperature up to ~75°C

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Work Already Carried Out​

To eliminate all possible hydraulic causes, the following components have been replaced:

Helm / Control Side​

• Original helm pump replaced
• Helm replaced AGAIN with a Seastar helm
• All low-pressure (pilot) hoses replaced

Power / Assist Side​

• Engine-driven high-pressure pump replaced
• Assist/control valve replaced TWICE (Volvo Penta 3862321)
• All high-pressure hoses replaced

Actuation​

• Steering cylinder (ram) replaced

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Current Situation​

Despite replacing effectively the entire hydraulic steering system:

• Drift still occurs exactly as before
• No improvement from any component changes
• Behaviour is consistent and repeatable

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Key Observations​

• Drift only occurs when system is “live” (engine running)
• System behaves perfectly when static (engine off = locked position)
• Wheel remains stationary during drift → helm is not driving movement
• Issue persists regardless of engine speed

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Current Understanding​

Based on everything replaced and tested, the issue appears to be:

A very small hydraulic imbalance or mechanical bias allowing the sterndrive to move slowly when the system is pressurised.

At this stage, likely possibilities include:

• Minor internal leakage still present in system (even with new components)
• Extremely small imbalance in pilot/control pressures
• Mechanical bias or load within the sterndrive/transom assembly
• System “softness” around neutral allowing movement under minimal load

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Outstanding Questions​

• Has anyone experienced persistent drift on a Volvo Penta sterndrive system after full component replacement?
• Could this be related to transom shield / steering pivot tolerances or wear?
• Has anyone successfully resolved similar issues without adding check valves?
• Is a small amount of drift considered “acceptable” behaviour on these systems?

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Potential Next Steps Being Considered​

• Testing behaviour out of the water to isolate hydrodynamic effects
• Inspecting sterndrive pivot / gimbal / steering geometry
• As a last resort: fitting pilot-operated check valves to lock the cylinder

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Summary​

After replacing:

• Helm (twice)
• Pump
• Control valve (twice)
• Cylinder
• All hoses

…the steering still drifts.

At this point I’m trying to determine whether:

• This is a known quirk / tolerance issue
• There is something mechanical being overlooked
• Or whether others have found a definitive fix

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Any insight from other NC9 or Volvo Penta sterndrive owners would be hugely appreciated.

 

[PCUK]

I'm not familiar with this setup, but if everything has been changed then the problem is elsewhere. Can you isolate the power steering pump? remove drive belt perhaps and see if the problem persists. Not much help I'm afraid.

 

[spannerman]

I have never seen this fault, when you say control valve do you mean the shuttle valve on the inside of the transom behind the engine? The steering has a direct function from the helmpump with the engine off and goes through a shuttle valve, with the engine running the valve is activated by low pressure from the helmpump and allows high pressure fluid into the hoses down to the steering rams to assist the steering. It sounds like the valve isn’t returning to its neutral position after you have stopped moving the wheel, it should otherwise it would eventually drive the steering to full lock.
Without any input from the helmpump the high pressure fluid just circulates from the engine pump to the shuttle valve up to the engine room resevoir and back to the engine pump. It only goes to the steering ram when the shuttle valve opens wirh low pressure fluid from the helmpump.
When the system was bled was it done with the engine running? It should be and I know from having bled dozens of these D4/6 steering systems it can take 50+ turns lock to lock at the wheel to get all the air out, if there is any in the system this will affect the balance between the high and low pressure system. A quick check is to try and move the drive side to side, it should be pretty solid indicating the rams are full, any slack of say more than an inch or so means there is air in the system.
Hope thus helps.

 

[kljay24]

Thank you for your response it is really appreciated. The Lecomble and Schmitt helm was completely replaced. The engineers doing the work then temporarily replaced again with a Volvo Penta helm to see if there was a compatibility issue. It behaved the same. Intermittently the rear engine reservoir gets hot (I am guessing 55-70 degrees c other times it’s fine). This has been going on for a year since we brought the boat.

The engine has been bled when the engine is initially off then with the engine running but the engineers doing not have the correct L&S helm fitting for machine to purge it properly so it’s all manual the main control valve on the transom has now been replaced twice (with all associated pipes) absolutely everything has been replaced.

I am on the boat now as I write. I have notice the helm behaving differently this time. If I turn the wheel hard to starboard or port with the engine running it reaches full lock then I can feel the helm valve click but then the wheel will allow me to continue to turn it with relatively little resistance. Previously I am fairly sure it would lock at full lock and that’s it.

It’s it driving me mad, costing a fortune and we have been unable to use the boat.

Thank you for your input

 

[spannerman]

Its normal to feel a click when you turn the wheel hard to full lock but then it should not move any further, it may creep very slightly if you continue to apply pressure to the wheel, this I have experienced on many boats and consider it normal.
If you can continue to turn it there is air in the system or a fault in the helm pump, unlikely seeing as its new. A very simple question if you take the filler plug out can you see fluid? You should see a metal part which turns with the wheel and the fluid should be 1/2 inch over that.

 

[A_8]

As far as I understand, it can be a bit tricky and sometimes cumbersome to get all the air out of the system once it’s been opened.
It might not be the most likely cause in your case, but air pockets could still be something worth considering.
I experienced something similar on my D4-300/DPH setup. After the first trip in heavy seas—with a lot of steering input—the oil level in the steering pump suddenly dropped, and the boat wouldn’t hold its steering position and would start to drift.
In my case it became quite extreme, although it’s hard to say whether the issue was already there to a lesser extent and only became noticeable because of the rough conditions and constant steering corrections.

 

[spannerman]

I got interrupted before I had finished. The oil in the reservoir should never get that hot! There is an oil cooler for the oil down on the port side of the engine inline with the big hose that takes seawater up to the seawater pump, its strange that you say its ok some of the time.
With no input from the helm pump the shuttle valve should float into its central neutral position stopping any flow of high pressure oil to a steering ram until it is pushed out of that position when low pressure oil comes down one of the hoses from the helm pump, it seems that the valve isn’t centering for some reason giving creep on the steering. I still think it needs bleeding again, I use a 1 1/2 ltr coke bottle with a screw on adapter that comes with steering pump kits for filling, it has a theaded connector which fits a coke bottle and the other end fits the filler plug thread in the helm pump, I hold it upside down so the oil runs in and air comes out and then twirl the wheel lock to lock with the engine running and from empty it can take 40-60 lock to locks to purge all the air out, the bottle will need refilling a few times but this way you are pushing the air to the highest point and you can see when there are no more bubbles.

 

[ari]

Im assuming you mean that it wanders left and right a little bit when moving slowly?

I think I know the problem - it's a boat, not a car. They drift left and right a bit.

Solution. Don't try to hold it on a laser guided path, it's not a car, you're not going to crash into other boats (unless you're REALLY doing something wrong).

Just guide it gently and let it wander a bit.

 

[oldgit]

First reaction, smaller craft with sterndrives do sometimes have a difficulty holding a heading when underway, possibly due to being
affected by breeze , most annoyingly noticable when on a long reach with Auto Pilot engaged .
Can recall when using the auto pilot on a heading required for about 5 miles or so, that a couple of minor course corrections en route were usually needed. The drift of course tended to diminish the faster you went .
Does trimming the bow down improve matters.The curious bit is when boat is stationary ?

 

[spannerman]

I think we are mixing up a hydraulic problem with all single sterndrive boats tendency to wander at slow speed. Many don’t realise that a boat hull steers from the bow and its when the helm is put over pushing the stern to one side this causes the water pressure from forward motion to act more on one side than the other so the bow is deflected. This works great on displacement and boats with a keel. But on planing hulls with a sterndrive there is a lot of bow in the water before you are on the plane and very little at the stern to keep it straight so they tend to wander often made worse by trying to correct it. As the speed increases and the bow starts to lift things start to settle down and at higher speeds the sterndrive has a natural stabilizing effect. You will notice if the helm is left straight agead the boat will develope a natural pattern of swinging left and right, it swings so far then starts to correct itself as now the drive is presenting more surface sideways in the water which then tries to balance it before it overshoots into the opposite swing.You can test this by setting the steering to straight ahead and incrementally increasing the speed where at some point the boat will run where you point it.
It can help on some boats to lower the trim flaps at displacement speed as they then add drag equally at the stern. I experienced this while testing a 35ft coastguard boat with twin water jets, there was nothing under the boat to provide any kind of damping and it was a nightmare at low speed until you dropped the flaps then it went straight.
This is all IMHO and from 30 yrs of testing hundreds of sterndrive boats from all major European manufacturers.

 

[PCUK]

I fit single or twin skegs right aft that act as fixed rudders which totally transforms slow speed handling. Obviously, nothing to do with this problem.

 

[spannerman]

Smart solution.