Merc 470 Trim Valve Body Question

I am new to boating and to the forum. I have searched and can't find the information I need. I have a 1982 Mercruiser 470 with the pre-alpha drive unit. When the boat is under power the trim will slowly leak to where it is beyond the vertical position. When it is out of the water I can push the drive beyond this point as well. It will even slowly lower when in the full up/out position. I have had the rams rebuilt and it is still doing it and have bled the lines as well. I believe the check valve in the pump is bad. I have the Prestolite pump and valve body with the square resevoir. The resevoir is full and doesn't appear to be leaking anywhere as it hasn't lost any fluid. The motor seems to be working just fine as it raises and lowers as it should. It doesn't appear that these are built anymore. Can they be rebuilt or is there some replacement that will work in its place? Any idea on the approx price to rebuild or replace or should I just live with the annoyance of periodically raising the trim? Thanks in advance for any help.

Re: Merc 470 Trim Valve Body Question

That style pump hasen't been used in years, only real option is replacement with later pump, but for that kind of money I could live with the annoyance!

Re: Merc 470 Trim Valve Body Question

Do you know what pump would work as a replacement? How much do they run?

Thanks

Re: Merc 470 Trim Valve Body Question

If the original is not available and there is no repair option then Volvo AQ290 is always the best choice. has four ports using standard brake threads and a 12oz reservoir. runs with or without relays and delivers roughly 2000psi. Well designed trim system don't much higher in pressure because it will cause orings to crystallize. they run about $200 for a complete motor and valve body.