Prestolite trim pump

[swihartart]

Re: Prestolite trim pump

I've been down the long trim road you have and boy is it frustrating. I highly recommend going on ebay and buying a cylinder in good shape. I just checked and they are out there. actually there is a post with 2 good looking ones for $104 buy it now. I'm not promoting ebay but I picked a set up for $100 (I had a bad one also, same symptoms as you, also had a reverse lock that was out of adjustment badly) now I have a spare and it cured my problem right away and had alot less corrosion than the old ones.

I looked at rebuilding and read that they can be a real PITA and if you don't do it right, you get to do it again...and again...then what is your time worth, and the rebuild kit cost etc...

O rings that are on the "dog bone" on the bottom of your pump can be found at any hardware store...cheap. Mine blew too when the cylinder was bad, I guess because the pressure spiked trying to push the bad cylinder...orings are the weak point so they blow. No big deal to change.

 

[wolfscott]

Re: Prestolite trim pump

Thanks for the tip Sean. I have replaced the o-rings in the dog bone already. I ordered a rebuild kit yesterday. But I agree. I will do this once. If it doesn't work, I am not going to waste my time on it over and over. I do have a pretty good break-down diagram of the cylinder hoping it will help. I just hope I can get it done before the rapture this afternoon. Hee Hee. I will let you all know how it goes.

 

[wolfscott]

Re: Prestolite trim pump

Alright, my frustration level is through the roof. I rebuilt the bad cylinder. Gave it a test run, and Voila', all is well. I hooked it back up to the outdrive, and while running it up and down a few times to bleed the system, the other cylinder started to leak. Okay, Okay, go ahead and say it. If you rebuild one, do both. So, here I am, egg on my face, and oil on my hands, rebuilding the other one. This really does s**k.

 

[FLAT RATE]

Re: Prestolite trim pump

I seem to recall that after filling the older trim pumps with fluid that you were supposed to leave the fill screw loose aprox 2/3 of a turn to allow air to bleed out, am I having a old timers moment? Might be the problem with this if the air can't bleed out of the system.

 

[wolfscott]

Re: Prestolite trim pump

I left the fill screw out while trying to bleed the system, so I think I should be okay there. But that brings another question. Does the system need to be pressurized completely to work? I know it is a self bleeding system, but it also needs pressure right?. Not sure how that works. Check valve or ball perhaps? Hmmm...? Not sure. Maybe it needs to have the screw in, but loose as you describe. I will try that as well.

 

[fishrdan]

Re: Prestolite trim pump

The vent screw needs to be loose, so the reservoir can breathe.

The entire system isn't "pressurized" all the time, though it does need to be completely full of fluid, no air. When you raise/lower the drive it pressurizes different sections of the system and while the drive is up it's pressurized by the weight of the drive. But, it's not constantly pressurized as an AC system is.

I posted earlier to lower the aft end of the trim rams during bleeding, this helps get trapped air out of the rams. Also, look at the color of the fluid while bleeding, if you see it getting frothy with trapped air, let it sit and settle out. This might be difficult with the old prestolite pump as the fill screw hole is small, you might have to use a flash light. Pumping aerated fluid through the system will cause trapped air when the air settles out. Either way, it is a self bleeding system and the air should work it's way out of the system eventually.

BTW, how easy was it to rebuild the trim rams? Or, should I say, how easy was it to get the old rams apart so you could rebuild them?

 

[wolfscott]

Re: Prestolite trim pump

Okay, I guess I need to just let everything settle for a couple days. I am going fly fishing in Montana this weekend, so hopefully when I get back this may have settled out. I am going to leave the fill and bleed screws out, so we will see. As for the rams, surprisingly simple. Since everything is oiled, it all slides apart easy. The outer tube is brass, so taking the end caps off was a quick job. No corrosion. If I can't get these rams to work in the down mode, I can still push the drive down by hand. What sort of trouble would I run into if I were to take it out like that for a run? I mean, would it be a really bad idea, or is it something I could live with once? The kids and wife are getting antsy, and I don't want this thing down all summer. Has anyone ever run the drive like this, and if so did you encounter any issues? Thanks.

 

[fishrdan]

Re: Prestolite trim pump

You should only have to wait an hour or so for the fluid to settle out if it gets aerated, maybe less. I wouldn't leave the reservoir screws out as you never know when the wind is going to kick up, or you could drop some dirt in there putting the cover back on.

Going out with the trim not working doesn't sound good. If the drive gets kicked up out in the middle of the lake it''s not going to be easy to get it back down, wouldn't be fun jumping on the drive trying to get it to go down.

It's odd that you can just push the drive down by hand, is that with the pump running by the down switch or just pushing it down without the pump running? If it can be pushed down, I'd wonder if it can raise easily, by the force of the drive in reverse? The reverse lock valve should stop that, but since the system is not functional, well....

It sounds like this is getting to be a bear to troubleshoot. You could connect the pump direct to the trim rams, or reverse the up-down lines and see what effect it has on the operation of the drive. IE: goes down good now, buy will not go up.

BTW, I have a Prestolite pump I took off my old boat that's just sitting around, worked fine when it was pulled. I'm not saying that's your problem,,, but.......

 

[swihartart]

Re: Prestolite trim pump

Try this to see if your reverse lock is bad or out of adjustment. Mine was and wouldn't let the drive come up, the pump strained and the drive would not move if trying to trim up if I was in nuetral, once shifted into forward trim worked fine, turned out reverse lock was the cause.

Make note of how the reverse lock is positioned on the shift plate. We will call this position default or 0. It has marks like a timing setup. Boat not running. Take the shift cable off of the reverse lock. It's the part that sits on the shift plate, clear hose goes to it as well as one of the colored lines, I think grey.

You will be able to rotate the lock by hand without the cable attached. There are also notches molded/painted on it like a guage for adjustments. The reverse lock keeps the drive from coming upward when in reverse.

Place the reverse lock in a similiar position that it was in before removing cable (default), try the trim, it should behave the way it has been.

Now move the reverse lock position slightly either way and try trim again. If it doesn't help, go the other way from default or 0 position slightly and try trim again. If rotating the lock to a different position fixes the trim down problem, you've found your culprit. When I rotated mine back and forth I could "feel" a little resistance that indicated when the lock engaged / disengaged. It should only engage when shifting into reverse if my memory serves well.

It's in the manual how to adjust the reverse lock. But all cables have to be in good condition and properly adjusted or it simply won't work right the way the manual explains.

If you rebuilt one cylinder and then the other leaked then I think your cylinders may not be the problem. It would suck if you rebuild the other and the same problem occurs and worse yet they leak again from what could be too much pressure caused by a seperate issue.

Good luck, hope this helps.

 

[wolfscott]

Re: Prestolite trim pump

Thanks for the input guys. The drive has been in the full down position all weekend, so any air bubbles that were in the system should have risen to the top by now. I had the cover on all weekend, as well as a rag laid over the holes so that should have prevented any debris from getting into the system. I didn't think going out like this would be a good idea. Dan, you are right. This is really turning into a pain, but I have to work through this. Sean, I didn't think about the lock being a problem. I will look into that as well. You know, this can really make a guy feel and look stupid sometimes. I am going to try a couple things, reversing the lines on the drive, as well as check the reverse lock. I am curious of something. The manual shows a lot of info regarding pressure testing the unit. Is the test unit something that can be built or would one have to buy the unit? This is really frustrating. Right now I am pretty much looking at anything to make this work. Thanks again guys. And the work goes on. One other note. The drive can only be pushed down while the button is pushed. This indicates???????

 

[wolfscott]

Re: Prestolite trim pump

I finally got it. After extensive research, testing and numerous trials and errors, I had realized, with help from my beautiful bride I had missed an essential part of reading in the manual. This is the shock piston test. It was right there all along. How could I be so foolish. Anyway, all of you who have had this problem take heed. Inside the trim cylinder is a part called the shock piston. This, on my particular cylinder is a multi-piece unit. It has 5 springs, 5 check balls, and 5 small "shock pistons". The pistons are actullay small tubes of brass flared at the ends like a trumpet. The check balls go in, then the pistons, then the springs, washers, and then the bolt and nut to tie the whole thing together. Upon close, and I mean close inspection, the shock pistons, on the flared end are all split. As if the flare had been cut, thus allowing the fluid to pass through, by passing the check balls. As this happens, both sides of the cylinder fill with fluid, thus creating an equal amount on both sides of the ram. Voila!! as the drive is raised, the fluid returns to the pump. As it is lowered, the entire cylinder fills. This is bad. So, the problem has been identified. Now, again after extensive research, the complete repair kit for one cylinder is an astounding $130.00, simply because it has been identified by mercruiser and most other parts places as obsolete. So, here we are. The battle my friends is half over. Thank you all for your help and insight. If anyone hears of another boater with this problem, send them here. I will post more as the repairs continue. Dan, I hope to see you soon on the lake.

 

[swihartart]

Re: Prestolite trim pump

wooah!!!! nice work dude!!! I never tore my cylinder down so I would have never thought of what you figured out. I'm glad you got it solved but it does suck that you get to pay way too much cause it says merc on the package. Ebay rules when it comes to good stuff cheap but if you had taken the easy route and bought cylinders you would have not learned what you've shared with us.

Pretty cool...I'd like to see you at the lake, cause that would mean I would be in Vegas!