Trim tilt leak down

[jobfish]

I am hoping someone can help me. I have a 1979 288 Mercruiser and I'm having trouble with the trim tilt. The trim goes down when underway. At first it was stuck at the top and would not go down at all... so I opened the hoses on the trim cylinders and let some pressure out... and now it moves up and down freely. The only problem is that it now leaks down while underway. I cannot find any external oil leak and I'm hoping someone will be able to help me diagnose this problem.

 

[achris]

Without an external leak there are only 2 places oil can return and allow the drive to 'trim down' on it's own.
1) An internal leak in one or other of the rams. ie an 'o' ring bypassing, or
2) the valves in the bottom of the trim pump is bypassing....

I imagine that by the year you have a Prestolite pump and 'internal return' rams.

Do you have a factory workshop manual?

Chris........

 

[jobfish]

Hi Chris,
Thanks for your reply. I do have a workshop manual. I'm not sure if it's a Prestolite pump but it has internal rams... it also has a single solenoid metal reservior external valve control. Is there a way of determaining whether it is the valve control or the 'o' rings in the rams without a test cage?
Cheers.
Bob

 

[thumpar]

I assume you have checked the fluid?

 

[jobfish]

Yes you assumed correctly thumpar plenty of fluid.

 

[achris]

Hi Chris,
Thanks for your reply. I do have a workshop manual. I'm not sure if it's a Prestolite pump but it has internal rams... it also has a single solenoid metal reservior external valve control. Is there a way of determaining whether it is the valve control or the 'o' rings in the rams without a test cage?
Cheers.
Bob

Not sure what a test cage is, I'm assuming it some form of pressure test rig.... :noidea:

What I would do it to isolate one ram at a time. If the drive doesn't drop when one of the rams is isolated, that's your culprit. If it still does it then it's the valves. The rams have rebuild kit available, the valve block does not... But I believe one of the aftermarket mobs are doing them....

Chris.........

 

[jobfish]

Thanks, Chris. I've tested the rams, port side went down with not much pressure at all. Any tips for rebuilding the rams? And I see that there are two different styles of rams for this model, do you know if they both use the same repair kit? As I can only find one repair kit for this engine.

 

[achris]

The only listing I get for your rams are "internal lines" or "external lines". If you have internal lines (ie both hydraulic hoses go into the ram at the front) then the kit is -445522A3. That's should be the only kit you need. If the end cap is difficult to remove, it might be worth get a new end cap too. Although, once you've bought those it might be cheaper to just buy a new complete ram from the shop.... http://www.sterndrive.cc/Mercruiser-Alpha-One-Gen-I-Trim-Cylinders.html

Chris......

 

[jobfish]

Thankyou Chris

 

[fishrdan]

Do your trim rams have both lines attached aft (front end)?

I rebuilt a set of trim rams with the aft line connections and the generic kit for 1970-1980 trim rams (Sierra) that supposedly had all the seals, was missing a couple of seals. I Emailed Sierra and they sent me a couple seal kits which solved the issue. A pain as it delayed the project, but 2 rams rebuilt for $40 was great.... Check your Mercruiser manual as it should have an exploded diagram of the rebuild process and seal location, will help identify if there are going to be missing seals from the parts kit.. These were trim rams off a 72 Mercruiser, MC-1. Here's the description of the kit I bought, google it.

P.T. O-RING KIT | GLM Part Number: 87410; Sierra Part Number: 18-2291; Mercury Part Number: 25-60342A2

The rams were pretty easy to rebuild, but I didn't have to figure with the end caps, they came right off with little effort. This was surprising as they were 40 years old, and I'm pretty sure they were virgin rams as the ols seals were as hard as a rock, brittle.