Re: 1979 EVINRUDE 150HP TILT TRIM PROBLEM
PSW.... If after trimming up, then letting it sit awhile, then the unit trims down... that would be a flaw within the oil pump itself (2 ball check valves) whereas it takes awhile to neutralize. Something one can live with.<br /><br />If the unit will not go down after trimming up regardless of the time it may sit in that position, I'd suspect a sticking shuttle valve. The location of the shuttle is: Look dead on at the PTT assy port aft (left back) side in the up position. You'll see a large slot (check valve) there. In back of that check valve is the shuttle assy. Sticking is usually caused by a faulty "O" Ring on that shuttle.<br /><br />If on the other hand, you are speaking of a PTT unit that will not operate in the down mode after you have trailered the rig some distance, the following might apply.<br /><br />(PTT Hydraulic Lockup)<br /><br />If the engine has been trailered without having both of the trim rams pulled in, or trailered without even having the engine being supported by the trailering support, it is possible for the PTT to encounter a hydraulic lock up. The slight up and down motion, when trailering allows over 1700 psi of oil pressure to build up on the wrong side of the oil pump. Since the oil pump cannot exceed that 1700 psi, the unit is effectively hydraulically locked into position (the elec motor runs and does nothing).<br /><br />The proper method for trailering is to have the engine in a full tilt position and resting on the trailering support bracket, then have both trim rams pulled in to a point where the engine makes a jerking motion. At this point, immediately take your finger off of the PTT trim switch. Now, quickly and sharply, tap the PTT up button. This removes the vast majority of down hydraulic pressure but at the same time, the engine is solidly locked into position and cannot rock up and down.<br /><br />(The Cure)<br />Have the engine in the up position and supported so that it cannot fall. Look straight at the PTT assy.... you will see what looks like a large slotted screw on the port (left) side of the PTT assy, but which is in fact a check valve. Remove that valve and what you find inside which is a shuttle valve, and a spring on each end of that shuttle valve.<br /><br />After you've removed those items, look straight inside of that chamber. You'll be looking at the reverse side of another check valve. Look at the hole in the backside of the valve you removed. You will need a punch that will fit inside of that hole.<br /><br />Now, place the punch inside of the hole in that check valve that is still in the unit, and tap it rather sharply with a hammer. It will take quite a rap but the idea is to unseat the valve to release the hydraulic pressure. Watch your eyes as when you do release the pressure, it will have a tendency to spray out somewhat.<br /><br />After releasing the pressure, reassemble the shuttle valve, springs, and outer check valve. Fill the oil reservoir with PTT fluid, having the engine in the extreme full tilt position. That's it.
