How does the trim system work? Merc 470

[kd7nkn]

I'm rebuilding a 1979 470 with a Prestolite High Pressure Power Trim. I see the hydraulic pump and two solenoids but admit I'm a bit confused about how they work.

Is it as simple as each solenoid turns the pump in opposite directions? In other words, one solenoid turns the pump clockwise to lift the stern drive and the other turns is counter clockwise to lower it? (or vise versa) Too simple?

Oh, BTW, the boat I'm working on has only ONE solenoid installed, but all the manuals show two. I'm assuming that the other is simply missing.


Any help would be greatly appreciated!

Cliff

 

[Bt Doctur]

Re: How does the trim system work? Merc 470

depends, the early pumps used 1 solenoid for the "up" operation and no solenoid for the "down" operation.
blue motor lead is up, green motor lead is down.manual shows 2 solenoids

 

[kd7nkn]

Re: How does the trim system work? Merc 470

Thanks, that's good information! So essentially, gravity is the 'down' solenoid on the older units? Any idea what years that was the case?

Thanks again!

 

[Don S]

Re: How does the trim system work? Merc 470

Here is a page from Merc service manual #4 that explains how the single soleoid trim system works.

 

[kd7nkn]

Re: How does the trim system work? Merc 470

Thanks Don! That's exactly what I needed! I only wish I had had the chance to download manual 4 before they disappeared. Ah well.

Cliff