Mercruiser Trim thump

loun

Cadet
Joined
Feb 22, 2009
Messages
17
2001 Bravo 2 + 7.4 MPI

Occasionally while on plane and I trim down I feel a bang. While shifting when the boat is stopped or traveling at very slow speeds I observe the following:

Neutral to reverse is always smooth
Forward to neutral to forward = smooth
Reverse to neutral to forward = thump
Reverse to neutral, hit the down trim then shift to forward = 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?
 
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