Falling Outdrive

[emmurphy50]

Greetings...

1981 Mercruiser 470 on a '81 19.5' Wellcraft Sunhatch - Lifetime boater now getting into my first "real" boat.

Late last year, I replaced my failed outdrive with an SEI, which called the snow gods to an early winter here in upstate NY. The old hydraulic rams had external tubes for the hydraulic lines with interfered with the wider fins on the new outdrive (there is a service bulletin on this), as the outdrive was now a Alpha 1. I had a complete lower unit off another 470 I bought as a candidate outdrive replacement with rams where the connections were at the one end only (no external tubes) and replaced my rams with these. I worked the air out of the system (self bled) and the hydraulics work - I do not believe any lines are crossed. I replaced the external hoses to the rams also (the old ones were fabric) and did my best to work clean in a tough environment - no guarantees I was perfect. I also replaced the hydraulic line junction connection under the gimbal housing, and I think that is tight (the old one cracked when replacing the lines).

I only had my boat out a few times and found myself with some new hydraulic problems:

1) The outdrive now won't stay up. It may have initially but does not now. It falls slowly and intermittently but over the course of hours, not days or weeks.
2) I can lift the outdrive with my hand. It also comes up in reverse.
3) It now sticks at times when fully up.

I see no evidence of leakage anywhere, certainly not the rams. There is some slight oil under my pump on carpet, but I am sure I spilled a little overfilling the reservoir. I did have to refill my reservoir - not sure if that was due to air working its way out of the system. The free motor spinning associated with the air pockets is gone.

I believe I have the prestolite pump.

Would welcome any suggestions where to start. Are the external valves replaceable separately a good starting point if I got foreign matter in the system?

Thanks,
Ed

 

[Bt Doctur]

air in the rams or the rams need a rebuild

 

[emmurphy50]

Even with no evidence of a leak? How would they fall?

 

[Bt Doctur]

the internal check valve/o-rings/check balls not sealing
http://www.boatfix.com/merc/Servmanl/6/6D5R3.PDF

 

[TyeeMan]

There are seals on the end of the ram ( inside) if the seals are old they may be allowing fluid to leak past the ram allowing them to fall. Could also be some schmutz or some particulate matter that got into the valve body of the pump allowing fluid to leak past the valve.

Try running the drive up and down a few times to see if something works loose.

 

[emmurphy50]

OK, I replaced the valve body on the pump today and still the same symptoms. I understand the rams are self bleeding, so it must be bad seals. One quick question - I changed from external tube to internal rams when I replaced by outdrive with an SEI Alpha 1 as the tubes interfered with the fins on the outdrive. That is OK, right?

 

[Bondo]

I changed from external tube to internal rams

Huh,..??..??

 

[emmurphy50]

The original hydraulic trim cylinders that came with the boat had an external line - meaning there was a stainless tube running the length of the cylinder that put fluid in both ends of the cylinder. (one connection each end). The line interfered with the larger fins in on the Alpha 1 drive vs. the pre-Alpha drives. The newer cylinders have both hydralic connections at the end of the cylinder connection closest to the boat. I wanted to make sure that in changing over I didn't create a problem.

http://www.sterndrive.cc/Mercruiser-Alpha-One-Gen-I-Trim-Cylinders.html

 

[Bondo]

Ayuh,.... It shouldn't matter whether ya use the older 1" rams, or the later 1, 1/4" rams, so long as they ain't leakin' internally,....