I've got a trim pump that quit working on the "Up" side. I took it apart to have a look, and everything appears to be in good shape. There are no torn o-rings, broken springs, scarred check valves or balls, and the actual pump gears and housing look fine. After cleaning it all out, it still doesn't want to work. I can get 2000 psi on the down side, but only about 500psi (or nothing) on the up side. I set the bypass valves back to their original height dimensions when I reassembled the pump.

What goes wrong in these things, and where can you buy parts?

first i would check it out by putting power directly to the motor.

Mine was intermittent trimming up. It turned out that the trim limit switch wiring had gotten damaged under the bell housing and was shorting out. Does trailer trim work ok?

If its not wiring then there used to be a rebuild kit out there but supposedly discontinued. I found one at a small mercruiser dealer.

The electric motor is fine; I'm doing all my work on the bench. It may be a bleeding procedure problem: Oildyne pump bleeding instructions. Very interesting...

Dollar Offshore, I believe, used to repair those and had a test fixture to check output. I assume you're talking about the Kiekhaefer/Oildyne pump that is all metal and does not have a plastic bottom. I can understand why you'd want to repair it. I paid about $1100 for a new one a few years ago. Good luck!

chuck did you run the trouble shooting tree?

Bob - I don't have a copy of that, but suspect that my problem is related to getting it properly bled. If you take these things apart, there simply isn't too much that can go wrong with them mechanically.