1976 Merc 850 Tilt/Trim Problems

[jayboy67]

I just started having problems with my tilt/trim. Pump resorvoir is full. I had just flushed all the old oil out and replaced with new 5 wt motor oil as specified in manual. Now to the problem.<br /><br />When I trim it up all the way to the point the motor starts to labor them it locks up in that position. I tried to trim it back down but the pump just loads up and starts to stall. It is pressurizing the hoses because they start defecting under the higher pressure. The only way I can get it to go back down is to loosen a hose at the hyd cyl and let the pressure bleed off. Only about a tablespoon of oil comes out. If I don't bleed it it will stay in the up position for days without bleeding down. Then after letting the pressure off and the engine tilts back down just a fraction of an inch, at the cyl shaft, it works good up and down as long as I don't take it all the way up to the top. <br /><br />Only other problem is that when parked in the up, not to the point where it freezes in the up position, it will bleed down in just a few minutes and the engine ends up in the down postition. <br /><br />Are these related problems and is it in the pump or the hyd cylinder? Or both?<br /><br />Its the old onboard trim pump that mounts in the battery compartment.

 

[JB]

Re: 1976 Merc 850 Tilt/Trim Problems

Why ask on a non-repair topics forum???<br /><br />Moving to Merc troubles.

 

[Chris1956]

Re: 1976 Merc 850 Tilt/Trim Problems

Jayboy67, There is a check valve under the pump motor which assists the motor in staying in the position you set with the trim buttons. I have never had any trouble with this component, and I do not understand how it works. It is an aluminum casting with places for the four hydraulic hoses and springs and check valves and an adjustment. I would recomend you remove it and clean it in oil/gas or some other oil-based solvent. Maybe it has a clog or sticky parts.<br /><br />Alternatively, if the check valve is good, a bad hydraulic cylinder piston seal will cause leak down. To isolate this, disconnect a single trim cylinder, plug the hoses and see if the motor still leaks down. If so, repeat with other cylinder. it is unlikely that both piston seals are bad. Repair kits are available from the dealer, and perhaps aftermarket. Good luck.

 

[jayboy67]

Re: 1976 Merc 850 Tilt/Trim Problems

Thanks Chris1956 for the response. I know about the valve area and do plan on taking it apart to clean and inspect. Have located a source in FL for the 4 O-rings that go in there and the body gasket/seal. My manual only says that the part is not servicible because of the close tolerances, except the o-rings, and doesn't really tell what is in there or what it does. My guess is that is the guts of the pump, gear train, the check valve, the pump mechanism itself. <br /><br />The pump is no longer available nor is the valve component. Also would cost about $600. If your suggestions don't work guess I will try to locate a used unit(s) to scanvenge parts from. <br /><br />I wonder if closing and opening the control valve might clear something inside. It says you can close it and lift the motor manually so it must bypass the pressure on both sides of the piston. Worth a try anyway.<br /><br />Wish someone that knows the workings of the pump would let us know just how it works. Mainly curious.<br /><br />Thanks again, jayboy67