Gears knocking?


Old 08-12-11, 07:18 AM
Thread Starter
Join Date: Oct 2003
Location: usa
Posts: 136
Gears knocking?

I have a 2004 21' Larson 210 LXI with a Mercruiser 5.1 MPI. I haven't had it out much in the past couple of years. The engine starts fine but it won't really get moving until I warm up the engine for about 10 minutes. In the mean time when I try to get it moving I hear the gears banging so I pull back on throttle, move at a very slow speed, wait and hope. Sure enough after 10 minutes or so everything works fine. Any thoughts would be appreciated!
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Old 08-13-11, 06:52 AM
Join Date: Apr 2007
Location: Near Buffalo, NY
Posts: 4,239
Alpha drive?

The powertrain includes a coupler (rear of the engine through the transom), two sets of u-joints (inside the top of the drive unit) and a transmission (bullet-shaped at the bottom of the drive unit). All of it is constantly spinning whether or not the transmission is in gear.

A coupler will tell you if it's getting ready to fail by shedding tiny metal shavings into the bilge where the transom meets the hull. It's not a common problem, but one possibility.

The u-joints are not lubricated by general maintenance. You have to pull the drive to get at them. It's good practice to pull the drive once a year and check them for tightness. The telltale signs of u-joints going bad will be a strong chatter when the steering wheel is turned so the drive is all the way to one side or the other. When the drive is raised all the way it's normal to hear some chatter from the joints, but it shouldn't be excessive. Don't rev the engine past 1200 or so with the drive all the way up.

The transmission and top gear set are lubricated by the gear lube inside the drive unit. The drain screw is located on the bottom port side of the bullet. If you loosen that screw and see water drip out you have a bad seal somewhere. (Check this after the boat has been out of the water for at least a day to give it time for the water to separate.) Check the level by removing the lower screw, attaching a gear lube pump, removing the upper screw (port side of the square part of the drive), and pumping a few ounces of lube into the drive. A drive that's full will immediately expel lube out of the top hole. This gear lube should be changed at least once per season.
Old 08-13-11, 11:48 AM
Nevar's Avatar
Join Date: Dec 2010
Location: USA
Posts: 28
RJ beat to my first point.
But also look to see if the shift interrupter is working. [ kills the RPMs for a split second going into gear]
Long warm up I'd look at a thermostat

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