Power Trim System Problems

[myoldboat2]

1974 Mercruiser 140 s/n 388xxxx
Mercruiser "Late Model I" Stern Drive s/n 390xxxx

Hello,

My sterndrive started pulling up when in reverse... I'd have to trim it back down. I went today to look at a reverse shifting problem (might be related), and when we took the support strap off the sterndrive, the sterndrive dropped down (never did that before). Turned on the power and tried to trim up... the trim pump ran but wouldn't "grab". Thought it might be low on fluid. Found oil on the bottom of the bilge. It's not engine oil, so I think it's the trim pump fluid.

I'm going through Mercruiser Service Manual #2 to try to figure all this out. But I'd like your guys input on where to start.

I assume I need to find the trim system leak. So should I refill it with fluid and run it to watch for the leak?

I'm not very familiar with the trim system. It has always just worked well. I've added a little fluid maybe once in a dozen years. So this is new to me.

Maybe it's related to the reverse shifting problem (see my other post). Maybe something to do with a reverse lock valve (if I even have one of those.......).

Thanks.

 

[86 century]

Re: Power Trim System Problems

Since the drive will not go up would say you are low on oil.
The only way I know to find the leak is to fill the reservoir and raise the drive.
If its a major leak the drive will fall shoving fluid out wherever the leak is.

 

[myoldboat2]

Re: Power Trim System Problems

OK, we will give that a try and I'll post what we find. Thanks for the reply!

 

[myoldboat2]

Re: Power Trim System Problems

Hoping to get outside tomorrow with my son to look at this.

In the meantime, I've been trying to learn about the power trim system. I think the fundamental problem I have is that I really don't understand this system very well. Could someone explain it to me, or point me to a post or tutorial online? I looked through the sticky posts but didn't see one. Thanks.

Here is the schematic from the Mercruiser Service Manual #2, Stern Drive Units and Marine Engines, pg 674:

.

 

[myoldboat2]

Re: Power Trim System Problems

I may have made some progress... I cleaned out the bilge and put about 1/3 quart (?) of fluid into the metal reservoir on the bottom of the trim pump. The sterndrive now goes up and down fully and there is no sign of a leak. I left it up all the way with no support strap to see if it drops over the next few days due to a slow leak.

Question: Is there a safety valve or purge valve of some sort that might let a lot of fluid out?

I still don't understand this system... what does the sender assembly do... how does the reverse lock valve work...

Thanks.

 

[myoldboat2]

Re: Power Trim System Problems

I think it's still leaking. Looks like a slow leak.

I read somewhere that sometimes a small "manifold" corrodes--a manifold of some sort that the hose go through the transom or into the stern drive? Where is that part and how would I access it? Things are pretty tight in the bilge.

Thanks.