1971 mercruser trim wont lower with out preasure on lower unit.

I have been working on a 1971 mercruiser stern drive. the tilt/trim wont lower properly. have to put lots of pressure on the lower unit to get it to go down. i pulled on hose off the rams. when i did their was air bubbles. doesn't appear to be any leaks in the ram o hoses. could it jus need bleeding or just over full. once some oil came out and air seemed to work little faster. still needed pleasure o get ram to go down. the oil had little metallic sheen to it.

oil that is full of air bubbles will compress. Is the drive bouncy when you put weight on it (spongy or springy?). That would be air. And 40 year old hydraulic oil could be the issue if that is the case.

As far as over full - no - it would just blow out the vented reservoir and fix itself
As far as bleeding - no - system requires no bleeding

You might take all hoses off and just see how easy the rams extend and retract - sounds like they may be damaged inside causing extra resistance to movement, and or bypassing.

What model of drive is this?
Some early Mercruisers had a pressure intensifier cylinder - do you have a 3rd cylinder inside the boat?

well I have another set of problems. the trim still doesn't go down. I have done some more checks on oil and system. when I press down on trim and have hoses disconnected oil comes out of the down hose. when I hook up the down hose to the ram and press down again oil comes out of the up hose. I am thinking the oil control unit is messed up. any place that has a diagram of this control unit the Manuel doesn't break it down that far.