TOPIC: Trim on 70 hp merc slowly lowers

Good morning
Been a long time away from this group,got some catchin up to do.
I have a 70 hp merc with tilt and trim and it slowley lowers all
the way to the transom in about 5 minuts.There is no oil leaking
out anyplace.Is this something an outboard hobbist should not
attempt to repair? Any help will be greatly appreciated.
Thanks , Jack in AZ

How old is the engine? Sounds like there is a restriction in the down circuit of the trim pump, there is a shuttle valve that releases the pressure when the pump is activated in the down position and it may be jamming up a little. Best thing to do is grab a factory manual for that engine and review the procedure for pump rebuilding and see if it is something you feel confident in doing. Not that hard to do but there are some special tools involved to troubleshoot the system.

Thanks
My engine is a 1987 and the complete tilt and trim is
mounted inside the transom bracket.This valve you speak of,
is it located within one of the three cylinders? I will be
picking up a manual for this motor this week.
thanks again , Jack in AZ.

Hi Jack,
You have the integral power trim. The most likely cause according my service school training is the pressure release check valve in the port side trim piston. I have not worked on many, but I would hate to try to remove the thread-in cover without the special tool or the tool that clamps around the piston rod to prevent the cover tool from slipping upward when trying to unthread the cover on the ones I did do (the cover was quite tight). I think that the piston assembly is no longer available from Mercury, so hopefully, the valve can be cleaned, and the piston reinstalled with a resolution to the problem. The service manual likely will be very helpful.

Regards,
Joe
www.fergusonpoolemarine.com
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Also make sure that you have enough fluid in the unit, tilt the unit all the way up and latch the transport latch to hold it up. Remove the fill cap and slowly add transmission fluid. Do not open the reservoir when the unit is in the down position, it is under high pressure.
Fill the reservoir until you cannot get any more in. Put the cap back on, release the latch and cycle the unit fully up and fully down. Keep your finger on the button until it "squeals" at the top and bottom. That squealing noise is the trapped air pushing past the relief valve. You need to chase the air out of the hydraulic side to the reservoir side. Tilt it up again, open the cap and add more fluid.
Repeat cycling, you should not hear any squeal at the limits, just the pump laboring.