1978 Johnson 175, 200, 235 HP Outboard Service Manual, Page 174Get this manual
STRIKING AN UNDERWATER OBJECT (See Figure 9-4) When an underwater object is hit, the shock absorber will absorb the shock and allow the motor to tilt upaThe shock absorber valves in the tilt cylinder piston open and allow the fluid at the top of the piston to flow to the bottombAt the same time that the tilt rod is being extended, the rest of the hydraulic unit is being et up for the return to water functioncHigh pressure fluid opens the impact sensor valve (2500 psi) dFluid passing through the impact sensor valve causes the letdown control piston to move and open the impact letdown valveeWhen the tilt cylinder piston stops moving outward, the impact sensor valve closes, keeping the etdown control piston pressurized, which in turn keeps the impact letdown valve open1m mediately after the impact sensor valve closes, the letdown control piston begins to "leak down" at predetermined rate