MerCruiser reverse interlock behavior

[gene8084]

I have a 1974 Mercruiser 188 I/O.​

Experiencing sagging of the outdrive and need to tie the drive up for trailering. I have rebuilt the RAMs but no change.​

I'm trying to isolate the problem before taking the more expensive (~$300) route of replacing the pump with a newer model that would allow by-pass of the original reverse lock.​

How does the reverse lock work and what part does it play in ensuring the outdrive stays in the up position?
What is the default position of the reverse lock valve? Open/Closed
Does power to the reverse interlock switch open or close the valve?
Is there some way I can test the electric switch dry? (i.e. remove, key to on, shift to reverse/forward or trim up/down?​

Thank you.​

As always, open to other suggestions and troubleshooting tips.​

 

[Fishermark]

Re: MerCruiser reverse interlock behavior

I recently went through this on my dad's Searay... but to be honest I was unsuccessful in deciding the problem. I decided it was in my (and my dad's) best interest to replace the system with an upgraded pump and forget all the stuff associated with the old system.

Having said, that, here is a diagram of the old. It may help.

 

[achris]

Re: MerCruiser reverse interlock behavior

The reverse interlock is only hydraulic. It stops the drive from kicking up when reversing, by closing and thus stopping fluid from being forced back to the pump. The electric switch is there to stop the pump being run while the boat is in reverse, because the hydraulic circuit is closed by the interlock.

Even if the interlock was bypassing completely, it would not cause the leg to drop... The most likely cause of the problem is either fluid in one (or both) rams bypassing the 'O' ring on the piston, or the check valves in the pump not closing properly... Rebuild kits for the rams are cheap, a new pump is not... And no, the valves can't be serviced... Part of the pump body.

Chris............

 

[gene8084]

Re: MerCruiser reverse interlock behavior

The electric switch is there to stop the pump being run while the boat is in reverse, because the hydraulic circuit is closed by the interlock. ............

Ah, got it. This makes sense. I was thinking about the switch controling the interlock...but your saying it's the shift motion.​

... The most likely cause of the problem is either fluid in one (or both) rams bypassing the 'O' ring on the piston ...

I already rebuilt the rams thinking this was the problem. No luck.​

Looks like I'm into a pump replacment.​

Thanks Chris​

 

[Bondo]

Re: MerCruiser reverse interlock behavior

Looks like I'm into a pump replacment.

Ayuh,... You'll be needing the 2 new Hyd. lines too, for the Swap....

 

[Don S]

Re: MerCruiser reverse interlock behavior

You may also have a bad seal in one of your trim cylinders, or even some dirt in one of the small check valves in the trim cylinders. If one seal leaks, the trim will slowly drift down.

 

[gene8084]

Re: MerCruiser reverse interlock behavior

More info. Isolating the problem. I raise the outdrive and put the remote in reverse. == The leg stayed right where it should.

Guess that confirms there's no problem with the reverse lock. The switch is working as expected (in/out don't operate in reverse).

Options:
Convert to new pump system $300
Replace the pump with rebuilt $175 +-
Replace the pump control valve ~100+-
Have the pump serviced/rebuilt $???.00

Opinions?​

 

[Bondo]

Re: MerCruiser reverse interlock behavior

Options:
Convert to new pump system $300
Opinions?

Ayuh,.... That's Mine....

 

[achris]

Re: MerCruiser reverse interlock behavior

I'm afraid I have to agree with Bond-o, again.

Chris.......

 

[gene8084]

Re: MerCruiser reverse interlock behavior

Thanks guys.

I know, pay me now or pay me later.

 

[achris]

Re: MerCruiser reverse interlock behavior

Thanks guys.

I know, pay me now or pay me later.

 

[fishrdan]

Re: MerCruiser reverse interlock behavior

Hope I'm not hi-jacking this thread...

But, what is required to swap from the old style hydraulic pump to a new style pump, just new hydraulic lines from the manifold to the pump? Will this cause any problems since the reverse lock valve will no longer be in the system,,, or is the reverse lock build into the new pump in some fashion.



If needed,,, I can start a new thread

 

[achris]

Re: MerCruiser reverse interlock behavior

Just remove the old pump and the reverse lock valve, connect a new hose to the old one where the reverse lock valve was and run it to the new pump...

There is no reverse lock valve in the new style pumps.. the valving is such that it is 'self-locking'... for want of a better word...

Chris......

 

[fishrdan]

Re: MerCruiser reverse interlock behavior

Thanks Achris,

Looking at Fishermark's diagram that makes sense,,, and I guess it would be a good idea to leave the trim indicator sender in the loop since my old drive does not have the trim sensors on the gimble ring. I was thinking I could just connect the pump to the manifold,,, couldn't be that easy.

 

[achris]

Re: MerCruiser reverse interlock behavior

Thanks Achris,

Looking at Fishermark's diagram that makes sense,,, and I guess it would be a good idea to leave the trim indicator sender in the loop since my old drive does not have the trim sensors on the gimble ring. I was thinking I could just connect the pump to the manifold,,, couldn't be that easy.

You're right, you need to leave the trim gauge sender in the circuit...

Nothing's ever easy!

Chris.....