1978 merc 140 power trim goes up on trailer but wont come down

[mirf1200]

Just bought a 1978 glastron fish/ske(17ft)140 HP and the power trim went up when the trailer button was hit but now it wont go down, the motor runs on the hydraulic unit but nothing happens. The dealer recommended tapping on unit just above the where the lines enter it (inside the boat) because the valves may be stuck from sitting. My question is could this be a fluid or air issue? The motor currently is in "trailer" position. Your thoughts appreciated. Mirf

 

[Solittle]

Re: 1978 merc 140 power trim goes up on trailer but wont come down

Yes to both questions. Your trim/tilt should have a screw that is a relief valve that will allow the lowere unit to come down - then check the fluid. Then cycle up & down to bleed any air out.<br /><br />Even better, since you bought the rig from a dealer, get him to do it.