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trim tilt issues

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  • trim tilt issues

    im new to boats so I im sorry for not knowing all the parts or names yet but I have a '72 mercruiser 165hp with an alpha 1 I think. when I bought the boat I could trim up but not down, the motor would make noise but no movement. the guy that owned it before rewired the trim system in a weird way so I went back to the original style controls and wiring. I had to jump with limit switch due to them not being available or a good system from what I read on here. now the top button does nothing, the middle button trims up, and the bottom button trims down for a short amount then goes up. im not sure where to go with this and am looking for help. I am a diesel mechanic and work on tractor trailers so I know my way around things but this trim tilt system in new to me. thanks for your help

  • #2
    I have a '72 mercruiser 165hp with an alpha 1 I think.
    Ayuh,...... Welcome Aboard,....... The drives used back in '72 were the MC-1s,....

    Alpha 1s came out 'bout 10 years later,......

    The trim system is a very basic hyd. system,......
    The trim motor spins one way for it to go up, 'n the voltage is reversed to spin the motor the other way to go down,.....

    You say the Po changed things up, so I donno exactly what yer lookin' at, pictures might help,.....

    The middle, 'n top buttons should make it go up, with the by-passed limit switch,.....
    The bottom button should only make it go down,......


    • #3
      It looks to be the original equipment. Any of the breakdowns I’ve found in a book or online show the set up as it is now. But yes the middle bottom goes up but the bottom button goes down for a short bit then it goes up. I was thinking perhaps the lines to the cylinders are wrong on one of them. Would that cause something like this?


      • #4
        bottom button down middle up until limit switch activates and drive stops top and middle together trailer, drive up all the way


        • #5
          yeah that's the way I have it wired. although I don't have the limit switch and sender on the sides like that, mine is a limit switch button on the top of the gimble. but like I said I just connected the two wires to by pass needing that switch. what Ive read is that this system is terrible anyways. but the problem im having is that it wont go up and down, just up. the down button goes down for a second but then up. im just lost as to what would cause this. would mixed up hydraulic lines at the cylinders cause this issue? I don't know what the previous owner may have done with things. im cleaning up his messes but im unsure as to how to get this to go up and down correctly


          • #6
            Look at the 4 hoses starting from the block under the gimbal housing. Front port on both sides go to the furtherest front port on the rams. Both rams are the same there is no L or R ram. There is 3k psi on demand to go up and only 800 down.
            Disconnect the rams on the drive end and try to rotate the push rods, they should be easy to rotate. If not then they need to be re sealed. The job should be easy for you and the kits are cheap.
            Sierra kit #. 18-2291 or Mercruiser # 25-60342a1.
            Be careful removing the check valve body, there are some really small ball bearings and springs. Note the direction of the valve before removing.
            Sometime the threads on the rams are corroded where they will leak.
            Sierra# 18-2148 trim cylinder housing.
            Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1


            • #7
              i took the ends off and rotated the rods, they move freely. and both hoses are hooked up front to front and rear to rear.
              Attached Files


              • #8
                Then there is a internal leak in the one of the rams. When you remove the cap and pull the internals out there should be a spool that is all the way in the front of the ram, sometimes you have to screw the cap on the ram tube After you remove the check valve then screw the cap on and bang it on the table. Look close and there should be a tear in the small “O” ring which usually causes the problem you are having. Flush out the fluid and re fill it with power steering fluid. The system self bleeds so just cycle it a few times.
                Also check the 4 bolts under the pump for tightness.
                Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1


                • #9
                  is there a way to determine which one is leaking? or just take them apart and see which one has issues?


                  • #10
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                    If you disconnect the rear mountings on the rams and cycle the pump might work.
                    Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1