my left drive, was off the boat no that its back on it will trim up but slowly drops back down in a few minutes. what might be causing this to happen? thx, rm

You need to do the "by the book" pressure test thing to be absolutely sure of where the problem is. But usually it is a feedback problem with a check-valve in one of the trim cylinders. If it passes that test, then it is a leaking check-valve at the pump itself. Hope this helps a bit. --- Jer

have you purged all of the air from the lines, etc. by running it up and down a few times?

If you have no external oil leakage it is the valve in the pump body, if it showed up all of a sudden it may be should be one of two things debris in the valve or the valve its self. One way or the other the pump need to come out. they are not a big deal to take apart to clean and replace the valves if needed. The parts are available through Merc, also you can fine the parts break down on BAM. The only trick to wookin on the pumps is CLEAN CLEAN! A very clean place to work on it, it must go back together spotless other then that it is darn simple.

Phil

Could it also be a bad seal in one of the rams itself? If one was bad, fluid would pass from one side of the piston to the other causing both a slow operation and a leak down drive. Had that problem on a buddies boat yrs ago. Rebuilt the rams and problem fixed.

Easy to check the pump, swap it with your other pump. The "by the book" test procedure is a pain in the A$$. Swap pumps and see what happens, should take all of 15 min.

If that doesn't work, try swapping rams. A bit messy but at least you won't be guessing on which parts are bad.

You can check the trim cylinders by running the drives all the way down and taking offf the up hoses and hiting the down button if oil comes from the open ports you have an internal leak in the cylinders, as far as replacing a valve in the trim pump save your self the hassle and get a new center section for it without pressure guages it is not possible to set up the new valve. Ed

had same prob on 35 -- trim pump rebuilt.

Emailed you the "book"