Trim system issues 2001 7.4 L

[loun]

2001 Bravo II + 7.4 MPI Merc

Occasionally while on plane and I trim down the drive thumps like it is slamming forward.

If I shift into reverse (pausing in neutral) then into forward drive thumps. If I trim down before I shift into forward the shift is very smooth.

It seems like there is a loss of pressure but only on the down side of the cylinders. Could this be the check valve in the trim pump or is it more likely one of the cylinders has an internal leak or something else?

 

[Bt Doctur]

Re: Trim system issues

page 6-4 this link. You might be missing the "Trin In Limit Pin"
http://www.boatfix.com/merc/Techbk/97/97hs6.pdf

 

[loun]

Re: Trim system issues

Thanks Bt Doctur, I will check for that part this weekend. This makes sense for the way it is behaving, but if this was missing wouldn't it thump in both directions?

Since it is only happening in the one direction I thought it might be a hydraulic issue.