I have a 2005 Profile 29' Cat with a Mercury 575 SCI.
It has a single ram add on hydraulic steering system. The steering worked fine on the boat until it developed a leak (which was an -AN fitting) which was fixed, added fluid and the steering has never been right since. Seems to move easy at idle. But when the boat is on plane it is very hard to turn and if you crank on the wheel it sort of chatters and seems jumpy/unstable.

In attempt to repair this the following has been completed/replaced-
-Brand new Mercury racing power steering pump
-Brand new Mercury high pressure line
-Brand new Mercury return lines
-Brand new brazillain manifold
-Brand new steering cable
-I've also replaced the IMCO external ram with what I believe to be a good used one (no change)
-I've also replaced the rear steering rack/actuator with what I believe to be a good used one (no change)

- I have the external hydraulic lines on order that go from the transom to the external steering ram
- I also have the internal hydraulic lines on order that go from the braziallain manifold to the transom.

Other than replacing those remaining hydraulic lines in hopes of one being collapsed. Has anyone chased this issue before? or have any suggestions?

Thanks in advance, Tom 732-334-8490

Many add on systems act just the opposite of what yours is doing. They are hard to turn at idle and if you try to turn fast at idle, the steering wheel will briefly stop because the PS pump can't circulate fluid fast enough. Not sure what could be going on with yours.

Worked fine until it leaked and now it has issues. I would think it needs to be bleed

Sounds like bump steer, which usually is air in the system, when I did my add on kit years ago, it bled itself out after about 10 lock to lock turns always making sure fluid was full before returning to center
this was over 10 years ago so my memory could be alittle fuzzy

I agree it does seem like a "bump steer." I have bled the system many times lock to lock with the reservoir full. both on the trailer and also took it for many sea trials hoping it would clear up. No change

is there a specific type of fluid that needs to be used for this system? I have always used ATF

ATF is fine. I use hydraulic oil for tractors without any issues.

Have you tried bleeding the outside by cracking the lines and letting it run?