Prestolite trim pump

[wolfscott]

Okay folks, I am confused here. I am running a 1973 mercruiser 165 I/O. It has a prestolite trim pump. The other day the clear plastic tube from the resovoir to the top of the pump let go, so I replaced it. I filled the resevoir, bled the lines, bled the trim cylinders, and gave it a test. The outdrive runs up fine, quicker than before, but on the down cycle, it hangs up about 3/4 of the way down and stops. I can have someone hold the down button in, and push down on the drive, but it will not go down by itself. I don't know if I am missing something here or not. Everything had run fine until I replaced the tubing. There is no pressure relief valve on this unit. To old I guess. I took the bleeder screw out as well, thinking maybe that would help. But nothing changed. One thing it does do is at full up, it slowly bleeds off and lowers the drive. Am I looking at a pump seal gone bad maybe? Any help or thoughts would be greatly appreciated. Thanks in advance.

 

[dubs283]

Re: Prestolite trim pump

if the drive bleeds down on its own then you have a leak somewhere

take some brake cleaner and spray everything down so it is dry, inside the boat and outside

run the system up and down a few times and check for leaks

 

[wolfscott]

Re: Prestolite trim pump

Thank you for the response. I have brake cleaner so I will give it a try. Any thoughts on the drive sticking on the way down?

 

[dubs283]

Re: Prestolite trim pump

- air in the system
- end cap seals/o-rings sticking

the system is self-bleeding, you just need to run the drive full up and full down 3-4 times to bleed air out, then recheck fluid level in the reservior

 

[wolfscott]

Re: Prestolite trim pump

Thanks Dubs. I did find a small leak on the trim limit switch, but it was a couple of loose screws. I tightened them up, and so far so good. Now since this is a pre-alpha, it does not have limit switches on the gimbal housing, only on the inside of the transom. When you say the end caps, do you mean the caps on the cylinders? And if that is the case, simple marine grease to lubricate them? I have the manual for this pump, but it's sort of short on info. Thanks for the help. I have run the drive up and down a few times, and the reservoir is full, its just this sticking thing that has me baffled. I will check the seals.

 

[dubs283]

Re: Prestolite trim pump

yep - end caps on the rams/cylinders

when the drive does "stick" can you go outside the boat and manually raise or lower the drive a bit??

if so, then you still have air in the system

 

[wolfscott]

Re: Prestolite trim pump

Yes, I can push down on the drive and it will lower. So if thats the case, I need to go back to the book and see if I missed something. Getting frustrated, I probably skipped a part. I will let you know. Thanks Dubs.

 

[wolfscott]

Re: Prestolite trim pump

Okay, here are a few pictures of the transom area above the engine. Disregard the broken shifter cable with the tie wire. That has been replaced. What I am showing is the trim limit switch, of which there is nothing in my service manual. It has a small leak around it, and it has seals inside. But I do not know where to get part numbers for this. Has anyone seen this before? A couple of the pics are of the pump. It is a Prestolite. The pump is working fine now, just a sticky cylinder. Thanks Dubs.Any help is greatly appreciated.

 

[dubs283]

Re: Prestolite trim pump

in your firsr picture, the trim limit is on the left, the switch on the right is the shift interrupt

unfortunately, the trim limit switch is NLA, not even an aftermarket one available, but you may be able to disassemble it and replace o-rings?? i have never had one apart so im not sure whats inside

there is air present in the clear line going from the pump to the switch, this is probably due to the leaking switch and the cause of the "stickiness"

 

[wolfscott]

Re: Prestolite trim pump

I took the trim limit switch apart and there are a couple of o-rings inside. One is small, inside diameter about the size of a pencil. The other one is bigger, about the size of a water bottle. Now here's the bad part. They are both flat. So...????? What to do, what to do? I am going to take it apart again, and get some pics of it to post. It looks like this is a learning experience for both of us, and anyone else who may come along. I do have to say this though, it kinda sucks not being able to get parts. I don't like to jury rig stuff, especially when you are out in the middle of lake mead. It's just to darn far to row. Oh, and just to make matters worse, I filled the reservoir this afternoon, and hit the switch. Now the seals underneath the reservoir are blown. This is where the clear tubing goes down under the pump, and the raise hose comes out. I can't catch a break with this thing. And to think this pump worked beautifully last year.

 

[dubs283]

Re: Prestolite trim pump

if they are flat, they are bad - you can get new ones at local hardware

unless you can see a definite "edge" on the flat part we have to assume they are not "quad" rings and are in fact old flattened o-rings

and what i mean by "quad" ring is, if you cut the ring and held it straight and looked down it, would it be square?? (an o-ring would be round if you did this)

 

[picklenjim]

Re: Prestolite trim pump

On the bottom of the reservoir is the manifold. This is the part that the clear line and up line conect to. If you remove it you will see it has 4 small o-rings between it and the bottom of the pump. You can get the o-rings at a hardware store. Very easy to fix.

 

[fishrdan]

Re: Prestolite trim pump

I think I remember reading this in an old Mercruiser bulletin, unbolt the trim cylinders from the drive's rear anchor pin and allow them to drop the the ground. (Put a long piece of cardboard on the ground so they don't get scraped up and so they can slide easily.) Run the trim up and down several times, 4-5 I guess, to purge the air out of the trim cylinders, pausing a couple of minutes between cycles to allow air bubbles to surface in the pump's reservoir.

I agree that the "square" seals they are probably old, hard, dried out, round seals. You'll probably have a better chance of getting those seals at an auto parts store than a hardware store here in Vegas. I'd try CAP or NAPA.

Oh, that hydraulic part that the 2 shift cables connect to isn't the trim limit switch, it's the reverse lock valve. It seals off the trim cylinders so the drive does not kick up when you power up in reverse.

 

[wolfscott]

Re: Prestolite trim pump

Thanks for the info guys. I took the bottom of the reservoir off and there was one of the o'rings flattened and ripped. So, off I went to autozone and got 4 new ones. I figured a/c system rings should work. After replacing them I went to work on the what we thought was the trim limit switch. After taking it apart, I discovered that there was a brass washer in the bottom, and it appeared to be cupped. I am assuming it is supposed to be, but it was upside down.So I turned it over which made sense to me. I am guessing it is acting as a spring/spacer? Also there was alot of play in the whole thing, so I replaced the rubber rings, cleaned all of the gunk out, and with a little permatex it went back together fine. I ran the pump a few times, filled the reservoir, and this stupid thing is still hanging up on the down. I bled the system like the manual says, and still no luck. I am going to try disconnecting the cylinders as you suggested and see what happens there. I really don't want to shell out the cash for new cylinders if I don't have to. I know they can be rebuilt. Has anyone ever done that? I am at a loss here. Simple hydraulics and I am baffled.

 

[wolfscott]

Re: Prestolite trim pump

So here is where we are at. This weekend I made a swap of the cylinders from side to side and voila', a bad cylinder. So, I am going to order the rebuild kit for that. This is no fun. At least the weather here on the weekends has been foul enough that going to the lake is out of the question so I don't feel like I am missing anything. Thanks for all of the insight guys.

 

[fishrdan]

Re: Prestolite trim pump

How did you determine that 1 of the trim cylinders was bad, disconnect both of them from the aft anchor pin and run the pump up-down? If you did, they might not extend/retract at the same rate, this is normal,,, though they both should go full in and full out eventually.

I've never rebuilt a trim cylinder but have heard the end cap can be a bear to remove,,, corrosion.

There was a guy out in Henderson advertising a bunch of used mercruiser parts on craigslist a while back, think he had some trim cylinders. It would be a roll of the dice on used parts though, could be as bad as the one you have now...

 

[wolfscott]

Re: Prestolite trim pump

Yes, thats exactly what I did. Both would raise(extend), but the starboard side would not retract. So, to eliminate the common block under the gimball,I swapped sides and the same cylinder did the same. Extend but not retract. So, that was pretty definitive for me. Now I have a question. I have found a couple different numbers on the cylinder. One near the eye that hooks to the aft of the drive, and one on the outside of the brass tube. So, which number is used for the actual unit part number, or is it somewhere else. Since this is a pre-alpha merc. I want to make sure if I get the whole unit it is the right length. When did you see the craigslist ad?

 

[wolfscott]

Re: Prestolite trim pump

Fishr, can I ask a foolish question, simply because I don't know. What is a trailering switch? And how would I know if I have one? On my trim/tilt switch I have three buttons. Two to raise and one to lower. Is one of these a trailering switch? Or maybe the other way around,I forget now.

 

[fishrdan]

Re: Prestolite trim pump

No dumb questions

I had the same 3 button tilt/trim switch on my old 73. Trim raises the drive about 1/2 way up, trailer raises the drive "all" the way up, past the trim limit switch. Problem is, the trim limit switch (on the transom assy) is usually bad on these old drives and was probably jumpered by the old owner. Press either of the "raise" switches and the drive will go full up,,, if it's jumpered. Since you are having problems lowering the drive, I doubt that's the problem.

Have you tried jumping 12V to the pump solenoids to see if you can get the drive to go full down. I don't remember which wire it is, green, blue, purple. Try them all and see what happens, the drive should either go up or down. It would help eliminate if you have a wiring problem, though, from the sounds of it, I think it's a hydraulic problem, not electrical.

When you push the down/in button, do you hear the pump making noise?

Gotta go, will check back later.

 

[wolfscott]

Re: Prestolite trim pump

I am pretty sure it is not an electrical issue. The pump worked fine all last year and I have not done anything to that wiring. I am convinced it is a cylinder gone bad. I found a o-ring rebuild kit on ebay for $10, so I am going to start there. My wife says I have a tendancy to over think things, so I am going with my gut on this one. Start out cheap and work up to the ladder. I will let you know how things go. The pump does run when the buttons are pushed. So I am pretty sure it's that cylinder.