Re: Trim goes up but not down and sounds like its working?
shuttle valves rarely stick. they commonly have 20-100 times more square inches than the poppet. In many OMC systems, the shuttle doesn't even have a sealing oring.
common hydraulic problems that cause a failure to lower .... debris gets stuck in one of the fluid intake balls and the gearplate simply pumps the fluid through both inlets without generating any pressure - the manual release valve is a tapered plug with two or more oring that separate the up, down, and bypass circuits. If the MRV becomes damaged it can short out the down and bypass circuits causing a system to lift but not lower - the system does not have a tilt limit and is raised hard against its stop creating extremely high internal pressure. a typical pump will have 20-30% higher pressure when the trim motor is spinning. When the pump spins in opposite direction the internal bypass or regulator on down circuit pops open before overcoming the internal pressure in up circuit.
I think, Don is most likely right in his initial analysis. If the motor is spinning but the system won't lower then look for mechanical problems first. when pumps break they usually bleed off pressure and gravity pulls down the engine on its own.
