Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-42794--1, Page 268Get this manual
ACAUTION Do not remove check ball components from trim rod pistonRemoval and reinstallation of check valve could result in improper operating pressure and possible power trim system damageIf check valve is defective, replace trim rod piston7Remove inner O-ring from piston
Trim "Motor" Removal
1Secure power trim assembly in soft jawed vice2Remove cap, washer and grommet from reservoir assembly