prestolite trim pump 1973-82 vintage

[buzzm19]

Hi guys, I am chasing down a slow leak down on my power tilt,( 81 mercruiser 260 ). this trim system has an external lock out and is ingaged when I am in reverse (it locls the outdrive from moving-up or down) when I trim the outdrive up and put it in reverse the out drive does not leak down which I believe isolates the problem that could be in the cylinders. Below the pump where the hydrolic lines attach to is a four bolt body that attaches to the pump (older guys call it the dog bone). In that dog bone is a valve that moves for trim up or down, there is a cap with a dowel pin in one side. Inside is like a small piston with rubber "O" rings. does anyone have any suggestions that maybe could be where the leak down problem is or do I have to dissemble the valve body for the fix, thanks Buz

 

[kenny nunez]

If you remove the valve block put a straight edge across the mounting holes that are the closest to each other, most times there will be a gap across the block. If there is a gap take a file and try to level out the surface. The “O” rings may be leaking between each other. The “O” rings are common and can be found at a NAPA or other auto store. I have never tried to take one apart and when I had my shop I just replaced it. I had a Mercruiser hydraulic test kit which was a big help and I do not have the kit any more.

 

[buzzm19]

Thanks kenner I did not think about that I'll check. I was also talking about the piston inside the dog bone?

 

[kenny nunez]

As I said before I never tried to repair that part you are asking about. Since the pump can generate 3k psi on demand on the up direction that is what causes the valve block to distort over time.