Marine Transmission Removal

Marine transmissions transmit power from the engine to the shaft and propeller of the boat. Depending on the brand and type, the transmission can operate hydraulically, similar to an automatic transmission in a car, or with a pressure plate and friction disk as in a clutch. Unlike automotive transmissions, marine transmissions operate in only one speed forward and one speed in reverse. These transmissions are subject to a host of adverse conditions that include the heavy shock loads of rapid shifting during maneuvering operations, high heat generation and variable alignment between the engine and transmission unit and the shaft. With its location low in the engine room bilge, the transmission is vulnerable to immersion during even moderate flooding. Remove badly worn or flooded transmissions for any major service or repairs.

Things You'll Need

  • Wrench set
  • Catch pan
  • Screwdriver or nut-driver
  • 2 bolts
  • Hoist
  • Shackles
  • Ratchet
  • Socket set
  • 2 pry bars
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Instructions

    • 1

      Remove the transmission-to-shaft coupler bolts using wrenches. Slide the shaft away from the transmission to gain sufficient clearance for transmission removal.

    • 2

      Disconnect the shift linkage from the transmission using wrenches.

    • 3

      Remove the transmission drain plug. Drain all fluid from the transmission into a catch pan. Inspect the fluid for signs of metal flakes or water contamination.

    • 4

      Loosen the transmission cooling line clamps at the heat exchanger with a screwdriver or nut-driver, if applicable. Remove the transmission cooling lines from the heat exchanger nipples. Plug the transmission cooling lines with a bolt, and tighten the hose clamps to prevent remaining transmission fluid from escaping into the bilges.

    • 5

      Connect a hoist to an overhead member in the engine compartment, if possible, or to a heavy timber placed across the engine room hatch. Connect the lift chain of the hoist to the lifting lugs on the transmission with shackles. Take up the slack in the lift chain using the hoist until the slack is gone. Do not over-tighten, or you will cause binding between the engine and transmission.

    • 6

      Remove the transmission-to-engine mounting bolts from the transmission, using a ratchet and socket.

    • 7

      Insert pry bars between the pry points on both sides of the transmission and the engine backing plate or bell housing. Pry both sides simultaneously to separate the transmission from the engine.

    • 8

      Slide the transmission off the engine output shaft until it is free of the engine. Adjust the hoist as you go to avoid binding the transmission on the engine output shaft while still supporting the weight of the transmission.

    • 9

      Lift the transmission out of the bilge with the hoist.