What's Wrong With My Trim Pump ?

[dennymac]

I've got a 260 and I'm using one of the mercruiser trim pumps, the one with the plastic reservoir....bought it brand new, and it's chattered when i go to the down position since day one....doesn't do it everytime, but almost anytime it's under a load...i've rebled it several times and it hasn't helped....it's a very pronounced shaking and chattering movement....anybody got any ideas..thanks, dmac

[Tom D.]

Sounds like it still has air in there some where or its sucking air. Check your hose connections. Does it hold the motor up over night ? Could be seals on ram to.

[sho305]

Had one once that did that and it was binding on the housing, the aluminum was sticking and grinding in there. A spacer or bushing was not right. Was an older drive though.

[BRENT GILL]

I KNOW WHAT'S WRONG. YOUR PUTTING MERCRUISER PARTS ON AN OUTBOARD. BRENT HEY WHAT'S UPPPPPPPPPP

[sho305]

I heard someplace to put a bigger i/o trim pump on my Merc 150 OB to make it trim faster. It has the pump in the boat and is a '73. It is kinda slow.

[Rickracer]

They are as fast as the Mercruiser pump (basically the same pump), and I sell them for $275.00 plus shipping. :cool:

[Greg Moss]

I don't think you will get the answer you are looking for here. I told you mine does it too. I think it has some thing to do with the cylinder volume and the pump valving. Mine only does it if you let it sit for very long then all I have to do is run it up and down and them it is good to go. I may have to do the up down thing once more during the day.
i think you need to ask some of the fluid power techs in that plant you work in. They maybe a little more up to snuff on hydralics that I am.

[sho305]

I have worked with them some on machinery I built. You can get a bouncing effect (oscillation?), particularly if there is anything compressable/flexable inline, like air or hose even. If the object moves freely with no load (such as the motor going down) it can make it worse. Something to dampen the movement will help if it is the hydraulics. Normaly you would first try to restrict the fluid going out of the cylinder to stop it. Not sure how you would do that on this system. On a machine, I would use a mechanical dampener like a shock absorber or friction clutch, or try to offset the weight with a spring or counterweight if I could not get flow controls to work. Try adding a little up or down pressure to the motor when you do it to see if it changes. If not it is likely a problem with the system like a bad valve, spring, air, incorrect sizing of components, etc. If it smoothes out then you just need to change the reaction of the moving weight somehow.

[Greg Moss]

I think that means you need some bungi cords like i got? :D

[steve]

if you are trying to run too thin of a fluid, it will do it . Or if you run a fluid that aerates too easily. What oil are you running? My mid did the same thing and I just ran a different oil . Now I have no problems. You also could try adjusting the pressures a bit and see if that helps.

[Greg Moss]

You may be on to something there. I hadn't thought about thicker fluid. I have been running the Sea Star steering fluid in mine. I may try some 20w motor oil. Let you know if it helps.

[Techno]

The hydraulics in these things aren't simple rams. The triple cylinder system is self bleeding and uses pressure and gobs of engineering to do all the things they need to do. I think this one uses tranny fluid.
All of the trim systems have to have some way of allowing the engine to kick up if it hits something. The single cylinder uses a free puck and a check valved piston attached to the ram. I don't know how its supposed to return since the 2 pistons are seperated by fluid now.
The book mentions using hot weather motor oil for hot weather use. When I took mine apart I found oil boogers in it but probably didn't harm anything.


I would guess its the pump, something to do with it since it started when you changed to it. Is this the kind you have to have vented? Some have to have the fill screw backed out 1.5 turns for venting.

[dennymac]

i've had a few people mention fluid....there may be something to this....i couldn't remember what i had used, so i looked and found the bottle i had labeled trim fluid and it was
dexron lll/mercon automatic trans. fluid...i bought the pump from key pucket and that is what he recomended at the time...maybe it's a little too thin??...Steve, what fluid are you running that cured your problem...thanks, dmac

[Casey]

dennis i run the same mercuriser pump as you and mine does it. at 1st when i ran 10/30w it was fine, then i switched to 10w motor oil. it was quicker, but i did notice a little chatter. when i switched to 5w fork oil it was even worse, but it is worth it for how much faster it is. just don't trim down under a load if you don't have to or you could put 10/30w back in and run 24v up. you carry an extra battery for your bottle warmer anyway.