Mercury 850 Power Tilt/Trim

The power tilt/trim works fine. It will not stay in place. I have checked the fluid level and bled the system. Once its up it slowly moves back down does the same thing when I plane it in the water. I can't find any leaks and I can't hear any air escaping. I ordered the maintenace manual for the engine but wanted inputs of where I should look next in troubleshooting.

It sounds like you have a bad seal in the piston itself which is allowing the fluid to leak back into the (resevoir). So the fluid is not leaking externally.

Wait for the manual - you may find it very difficult to find parts for this so don't take anything apart until you have a diagram in front of you...

The book I ordered is the Mercury Outboard Shop Manual: 45-225 Hp, 1972-1989 by clymer. Any idea if that book gets into detail enough to fix problems like this or should I have ordered something differant?

Is this an internal or external trim system. external being two rams and a trim pump in the boat. Check your reverse lock screws on either system and make sure they are tight but do not overtighten.

There are thing you should take apart and things you DO NOT take out on those systems. That book hopefully with help you but the merc manual for that system is Much better for a complete trim overhaul, remember that is a pressure system - WEAR safety glasses and use a Line wrench on the fitting and make sure you start the hose fittings with your fingers and square to the holes they are very easy to strip.

most of the parts in those that are replaced are o-rings and two small seals as each ram.

Its an external system

Got the book in today and its no help at all. My serial number is 4541016 and the title says it was built in 76. Where can I get the model # to make sure I order the correct service manual?

So I have a good book to work from today I ordered Seloc manual the last one I ordered was the Clymer book. I s there much differance between them?

Personally, I would never buy a Clymer's - I just find them vague on alot of things and they definately lack technical specs.

Seloc's is considerably better - much closer to the info contained in a factory service manual (if available).

I have more information on the power tilt trim. Besides not staying up and losing pressure when I go to reverse the engine comes up. Any thoughts.

It definately sounds like you have an internal seal/o-ring or valve that is toasted.

But since I do not have a schematic of your particular trim system I can't really point you to a specific component.

In general, when the motor is in reverse there is normally a valve in the system that will close to prevent it from "climbing".

On one of my trim/tilt systems there is 11 internal valves and a couple dozen seals - which is why I say that you need a detailed schematic of your particular unit to try and isolate what may not be working.

Something is obviously letting fluid pass when it shouldn't...