AZDominator

Starboard drive will not maintain its position. Every mile or two I had to reset "out" to match port drive. This is the first weekend I've had to do this. There are no external leaks and the level in reservoir has not gone down. Is there a bypass in the pump assy. that may be leaking by or is a trim cylinder leaking by. How do you check bad trim cylinders? Anyone know of any checks I can make to narrow down the problem? Help!!!

mcollinstn

If fluid level in the pump is not dropping, then you have a leaking check valve in the pump. Leaking cylinder pistons are rare. Also double check to make sure the manual valve is seated tightly in the pump (assuming you have a manual valve - some pumps have them, some do not).

As far as any bypass, the only one would be the manual release valve. A complete set of orings and check valves shouldn't run more than $30 or so.

AZDominator

Thanks MCOLLINSTN for the information.

MitchStellin

This is not uncommon. If the boat is on a trailer you should see the drive drop over night. With mine if the drive was all the way up it stayed there but if it was half way up it would drop. I never fixed it and sold it so I am not sure why. I was told the rams were bad and were leaking down.

AZDominator

This is why I posted this thread. As I said earlier, I have to reposition the trim every mile or so. What I failed to mention was on the trailer (with a nuetral trim position) the drive will lose all of its trim overnight (actually within 5 hours). I have never tried all the way out to see if it would fall. My shop isn't long enough to trim the drives out with the door closed. I'm hoping it is just the bypass in the pump and not the rams. Thanks again for the info.

toonatime

91 454Mag w B1 drive..mechanic had hard time
w diagnosis...replaced gaskets in trim pump w
rebuild kit to solve..

AZDominator

Just some feedback for any do-it-yourselfers: Pulled trim pump, removed motor and reservior. Removed the hex plug retainers (the 22mm plugs on either side of your pump) removed the spring and poppet vavles and found some small material (small painted alum. pieces) on the seat area of the poppet valve. No more trim problem, didn't cost a thing but alittle time. If anyone has a need to repair your pump reference Mercruiser Service Manual Number 28 for drive and trim related questions.