1978 Power trim and tilt

"I aquired this unit from a Jo

"I aquired this unit from a Johnson 150HP and wanted to try it on the bench before installing it on my motor. This unit has 3 wires (black, blue, and green)and has two trim rams with the large tilt piston in between. I placed direct negative to the black wire and alternated direct battery between the blue and green. The problem is that while the trim rams move up and down the main piston always moves in the up direction. The only way to lower it is to bleed the lower side of the piston. Does the unit need the weight of the engine to return to the down position or should the piston pull in by itself? The unit is normally wired with a solenoid but I don't think that should be affecting me for this test. The wires I'm using should be more than adequate for about 30 to 40 amps. Any help would be appeciated. Thank you.
Mike"

"With the unit off the engine,

"With the unit off the engine, the trim rams will pull in first, after which hydraulic pressure is applied to the upper portion of the tilt cylinder which forces it to lower (does not require engine weight).

The problem you speak of is usually caused by a malfunctioning trim/tilt seperation valve which is located in the port side of the unit... the one which would normally be hidden by the port engine transom bracket."

Joe: Thank you for the quick a

Joe: Thank you for the quick answer. I found the valve you were talking about and disassembled. There was a little gunk but nothing severe. I cleaned it up and blew out the passages with air. After assembling it appeared to try and pull down once but after cycling it once I am back to the same problem. Tried pulling it apart again and it was clean and when tried the piston just wanted to go up. Are the manuals still available for these? Would fluid make a difference? I am using power steering fluid. West marine sells a power trim fluid but its a little on the pricey side. Even more so when you lose a bunch every time you work on it.
Thanks again for your help.
Mike

"P/S fluid seems to work prett

"P/S fluid seems to work pretty well as you've already found out.

When you're facing the rear of the PTT unit, there will be a large slotted valve just under the port (left) trim ram. In back of that valve is a shuttle valve, and in back of that shuttle vale is another valve just like the first one. That shuttle valve may be sticking, have a cracked O Ring, or one of those valves may also be sticking or fouled.

So many areas to go wrong but these are the most likely."

Thanks Joe. I downloaded the d

Thanks Joe. I downloaded the diagram of the unit from the evinrude site and I see the shuttle valve you are talking about. Alot of Honey-Do work today so I'll look at it tomorrow and let you know how I make out.

"Do not want to interferr in Y

"Do not want to interferr in Your discussion, but I have been fighting those units quite a lot in my time to. The main thing I learne was never to mix trim fluid. They may have the same spec, but things seems to happend anyway. If it starts acting up in the way You describe it very often ends up in a seal kit and complete tear down with change of all seals and totally cleaning of the internals. Take a very good look at the pump housing itself. Inside there are two balls that controls the flow. Quite some times I have had to replace them, (not spare parts but took them from a ball bearing). I even used to carefully polish the sealing seat with a Dremmel. If You have a dentist drill it does fine! These units are more vulnerable to wear than the engine cylinders and cleaniliness is a must, and a couple of quarts of clean oil must be calculated for cleaning and refill. Never reuse oil that has been in the unit! Attaching a pic so we have a common reference, hope it is the right one!
"

Morten: You are not interferin

Morten: You are not interfering! You guys are great. I don't post much cause most of the time my questions are answered in someone else's.
To all: The unit in the picture is the one. Following Morten's advice I pulled all the valves and drained the unit. A doctor would be proud. There is not a speck of dirt. No valves appear to be binding and all springs are present and not broken. Joe: The shuttle valve is fine as best I can make out. Morten: The unit is now filled with the proper trim and tilt fluid. The ball bearings in the motor compartment look like new. I'm figuring my next stop will be the reservoir and take a look at the valves in the bottom of that. I'll keep you guys posted and as always thanks for the help.