Merc Trim Pump Problem - Help Please

[McGillicuddy]

Trim went out on Merc 4 hose tnt pump.
Motor was getting hot and seemed frozen... Replaced motor brushes and ground screw and motor whirs great now. But its not moving fluid into the hoses. Unfortunately when I removed the hoses, I think I failed to close the manual release valve before removing hoses. Any tricks to getting the pump to draw fluid thought it? I've already tried cycling trim up and down to bleed/prime and have disconnected the down hoses at the trim cylinders to try to cycle the oil into the hoses to no avail... any tricks to this? Seems simple but I'm stumped . The motor is in full up position, the reservoir is full, and the battery has plenty of juice... Any ideas? Thanks. Motor is an 83 Merc 115 I-6 and pump is old square reservoir/four hose model...

[Fr. Frank]

Remember the trim pump is just that, a pump. It only sucks soil from the reservoir, If your motor is turning, but the pump isn't pumping, check the fitting that goes between the motor and the pump. The motor shaft is designed to fit into a small adapter that in turn rotates the pump shaft. Make sure that the motor is actually turning the pump while it's spinning. Often, when the motor is mated back to the pump after replacement or repair, the small part that actually connects the two gets lost, ans it has a tendency to stick to the shaft of the motor as it is removed, but just long enough to then fall off on the bench somewhere, or into the bilge if you remove the motor while the pump assembly is still in the boat.
After that, disassemble and check the pump. If the pump was failing, that could have been the catalyst for the failure of the motor in the first place.
The four-hose pump is the same pump as the nearly identical-looking two-hose pump, only the manifold on the pump base is different. If necessary, you can pick up a two-hose pump and just put the manifold off the bottom of your pump onto your "new" one.

Oh yeah, you can get the motor down by opening the relief valve on the pump, and then standing on the lower unit to apply pressure. Don't bounce on it with your weight! I was told that bouncing on the lower can briefly quadruple the amount of force applied to the hydraulics, and may damage one of the old seals on the trim/tilt cylinders.

If that doesn't work, remove the hoses from the pump and put the ends in a small container of oil, and then stand on the lower unit. (The small container of oil minimizes the amount of air to bleed from the lines later)

[McGillicuddy]

Thanks Fr Frank,

I'll look into that connecting point of pump and motor.

The motor is in the up position only to fill the reservoir. It goes down manually because there is no hydraulic pressure in the empty hoses and cylinders.

[Fr. Frank]

Thanks Fr Frank,

I'll look into that connecting point of pump and motor.

The motor is in the up position only to fill the reservoir. It goes down manually because there is no hydraulic pressure in the empty hoses and cylinders.

Okay, I thought you were stuck in the tilted position. Oh, that pump is s'posed to be self-priming/bleeding. Open the manual release valve, and manually move the motor up and down a couple of times with the hoses installed. Now cycle the pump up and down a few times with the valve still open. Now close the valve and cycle the pump a few times again and listen to see if you get any pump pressure at all.

Failing that, do a quickie rebuild of the pump itself. (disassembly, cleaning, inspection, reassembly) The pump is amazingly simple inside.

On my desktop, I've got a diagram of the pump somewhere, from Mercury parts software of about 2006 or so. I'll see if I can capture that and send it to you later today when I go back to the church.