Outdrives, commonly called stern drives, consist of an upper and lower unit on boats. In appearance, they resemble the lower half of an outboard motor. They encase and couple the main drive gears to the propeller at a 90-degree angle for the purpose of thrust in either forward or reverse directions. The outdrive also contains the steering and trim mechanisms, which function by hydraulic fluid and controls, allowing the boat to rise or lower in the water and turn in side to side directions. Gear oil supplies the lubrication to the outdrive. Troubleshooting outdrives requires the inspection of various components and systems.
Trailer the boat and take it to a convenient work location. Wash the unit down with a sponge and soap and water. Dry with rags. Use a socket and wrench to disconnect the negative battery cable. Shut off the the main fuel supply line to the carburetor. Visually inspect the exterior surface of the outdrive unit for cracks in the casing, bent or cracked propeller blades. If you have vibration, you will need to check the propeller shaft.
Wedge a wood block between the propeller and the ground. Use a pair of wire cutters to remove the propeller nut cotter pin. Use a socket to remove the propeller shaft nut. Remove the spacer and pull the propeller from the shaft. Place a dial indicator on the ground under the propeller shaft and adjust the flex gauge dial pointer to rest against the shaft.
Place the boat in neutral and turn the shaft by hand. Any excessive lateral movement of the shaft expressed in thousandths of an inch beyond the run-out limitation in your repair manual, indicates a bent shaft. Examine the key-way on the shaft for rectangular, clean edges. The key-way should be sharp and defined. The shaft key should be rectangular, with sharp edges. Examine the thrust bearing on the shaft for wear marks and deformation. Replace any shaft key or thrust bearing that shows unusual wear. Reassemble the propeller.
Check the trim-tilt fluid reservoir for the proper level. If low, fill the reservoir to the proper level limit. Reconnect the negative battery cable with a socket. Activate the trim-tilt motor and look for smooth vertical movement from the top range to the bottom. Examine the trim-tilt cylinders for leaks. Any leaks on the trim-tilt shaft indicates a piston seal that must be replaced.
Turn the steering wheel in its full range to the left stop and the right stop. If the outdrive fails to reach its stop limits, adjust the steering cable length of one or both cables at their bracket locations, by loosening the bracket holding nut or bolt with a socket and resetting the cable tension. Tighten the bracket holding bolt or nut with a socket.
Use an Allen wrench or hex key socket to loosen the gear oil drain plug, but do so temporarily to sample the gear oil. Let a small amount of gear oil flow into a cup. Examine the gear oil carefully. Any indication of white streaks or white foam in the gear oil means water has entered the lower unit drive case. You must remove the upper case unit to inspect the U-joint bellows condition and the internal drive seals.
Idle the boat near a pier until the engine has warmed up to normal operating temperature. Shift from neutral to forward gear. Listen for any loud clunking sounds coming from the outdrive unit. Place the shift in neutral and then in reverse. Listen for any clunking or jolting sounds. Hook a tachometer positive lead up to the negative coil terminal. Hook the other tachometer lead up to a ground source. Read the idle engine speed. Refer to your owner's manual for the correct rpm specified.
Use a screwdriver to adjust the idle speed screw on your carburetor linkage to specifications. Turning the screw counterclockwise will reduce the idle speed and keep the transmission from hard-shifting or jolting into gear. Check the idle return spring to make sure it has not disconnected. If the spring appears weak, pull it and refasten it to another notch that provides more tension.
Check your shifter linkage at the control box, and where it joins through the transom. It should be well lubricated at the control box location. The shifter should move easily and attain all gears. If the shifter refuses to activate reverse or forward properly, adjust the linkage by loosening the cable bracket lock nut with a socket and moving the cable in the direction to lengthen or shorten the travel distance.
