290 DPE trim issues

ralph s3

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10 May 2021
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Hi All,

I’m having a battle with the hydraulic trim systems on my two DPE sterndrives. I’ve done quite a bit of work on them and I’m running out of ideas so I was hoping someone might have a suggestion. Here is the story so far;

I have re-wired the electrics and replaced all the relays and the pumps now work reliably in both directions. One pump has been replaced and the other has a new electric motor.

At the end of last season one drive (the one with the new pump) would hold the drive at various heights when under way (the boat is on the river currently so we are talking low speeds). The second drive would slowly drop when underway at tick over and would lift up quite quickly in reverse. It would also drop slowly if left up when not in use. When the boat was lifted this winter all the rams showed signs of leaking and there was water in the hydraulics on both sides.

So I had all four rams opened and all the seals replaced. The mechanics who did the work said the cylinder bores were actually in good condition.

However, both drives now both display the same behaviour. If at rest the drives are lifted by pressing the up button they will drop down again in a matter of seconds. When underway the drives will not stay up when going forward and will both lift up if run in reverse. It’s as if the drive seals have all completely failed. I am well aware that there is a chance that replacing the seals won’t work and that the rams themselves need to be replaced but I would have expected at least one of the drives to work for a short period if the rams were worn internally.

However, what’s really confusing me is if I press the up button to say position 25 and then use the down button to move them down to say 20 they will hold. I can drive forward and they stay in the 20 position. I can do this at any setting. As long as I use the up button followed by a very quick press of the down they will hold in any position 5,10, 15, 20, 25, 30 etc. They will also stay up in position for several days. This suggests to me that the ram cylinder bores must be ok as I can get the drives to hold in any position. If the seals had failed pressing the down button briefly shouldn’t make any difference. I was wondering if the pump body has a couple of non-return valves that aren’t closing correctly and the brief burst of down forces them shut. But again, what confuses me is that one of the pumps is new (although it is a non-OEM pattern pump). I have followed the procedure to make sure there is no air in the system (fully raising and lowering the drives 10 times). There is no sign of any fluid leaking from the drives and the hydraulic fluid itself shows no sign of water contamination.

Any ideas gratefully received.

R
 

BruceK

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8 Feb 2015
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So I had all four rams opened and all the seals replaced. The mechanics who did the work said the cylinder bores were actually in good condition.

You would think. Ive got spare sets of brand new rams never used in the garage that I sent in to a hydraulic specialist. i.e. all they do is rams, because I managed to cross thread the pipes. On both RAMs they had to apologize and replace the seals when they did their checks. You'd think replacing seals were easy but apparently they are easily nicked and torn on assembly too. However in so saying unless you replaces the entire pump assembly the valves are also a PITA. Best to replace the entire unit than service it. The effort to getting to all these things made me just throw in the towel and replace everything the third time. Its just not worth dicking about.
 
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