Mkeller

The power trim on my 1997 bravo 3 drive goes down very slowly- 3-5 minutes from trailer position to down. Fluid level is fine. All electric components seem to be functioning normally per Clymer manual. No visible leaks. Drive goes up fine. Pump is very noisy when I press down. Can anyone help me out?

Edward R. Cozzi

Have you been storing this drive in the "up" position for long periods?

Mkeller

Interestingly enough, the problem did show up after I left the drives up for about 2 weeks in October due to extremely high tides. I store the boat on a lift with drives down, but had to raise them to clear the fall high tides. What do you think the problem is? Do you how I can fix it?

Edward R. Cozzi

The trim rams may be sticking inside the tubes.
Have somebody stand on the drive while you hit the "down" button. Cycle it several times to free-up the inside parts. If the problem persists you'll need to rebuild/replace the trim rams. Mercruiser has always recommended storing the drives in the down position to avoid this problem.
Good Luck. Hope I helped.
Ed Cozzi

Mkeller

Tried that. I can get the drive down, but it moves real slow. Do you know if there is there any kind of lockout in the hydraulic system? Drive goes up fine.

Audiofn

As Edward said I am guessing that you have bad rams. Disconnect the outer end of the ram from the drive and see if you can rotate them by hand. You should be able to twist the end of the ram fairly easily. If you can not then you have a siezed ram. Check them all, even one bad one can cause issues. My Donzi does the same thing as your boat and I know it is the rams on my boat. The pump has a LOT more preasure going up then it does going down and that is why it seems to go up ok. I am willing to be however that when you find the issue it will go up a lot faster then it is now.

Jon

Mkeller

Thanks. I'll check it out.

BajaIceBreaker

No way... The pump is noisy?
Sounds to me like you are taking in air.

These are 2 way rams. They will push down just as easy as they push up. Somehow you are getting air in they system. Not sure how, but that's what makes the pump noisy.

US1 Fountain

iTrader: (1)

Ok, I'll take a stab at it.

It goes up easy because you have the full piston surface area to push it up. (more sq. in.) But on the down stroke, you are putting fluid on the back side of the piston, which has less square in's because of the rod. So if a seal was bad and fluid could leak past it from one side to the other, it has less force do to more surface are on the uppward stroke, hence why it works fine going up, even with fluid leaking past the seal trying to create equal forces on both sides of the piston, but the more surface area will have the edge.
Sound good?????

Besides, if air is getting into the system, wouldn't that mean there is a leak, at which point oil will be leaking out? Takes more fluid to raise it up.

f311fr1

Yes, that is correct. In hydraulics, flow is speed and pressure is force. If your rams are bypassing due to scored interior walls or worn seals you have less area for the psi to work on in the down mode due to the area of the rod subtracting from the area of the back side of the piston. The formula is pressure X area = force. Usually pressure is expressed in Pounds per Square Inch or PSI. Area is expressed in Square Inches for force and Cubic Inches for volume.