I need some input. Merc 115 lower unit.

I just bought a used 83 115 hp merc lower unit. Shouldnt there be some ratcheting sound from turning the shaft. I can turn it cw or ccw and no ratcheting sound is that ok. It goes into neutral and forward and reverse no problem. Just no ratcheting sound. Checked the fluid no shavings, and the fluid was dark black. I need to put fresh fluid in it.

Re: I need some input. Merc 115 lower unit.

Assuming you have the lower unit separate from the motor, hold the vertical driveshaft with one hand to prevent it from turning then you should see the following behaviors with the prop shaft using the other hand:

1) in neutral the propshaft should turn freely in either direction without resistance.

2) in reverse, the propshaft should not turn in either direction

3) in forward, the propshaft should not turn counter clockwise, but will turn clockwise and 'ratchet' as it slips over the clutch dog teeth

If the lower unit is installed on the motor, you don't need to hold the driveshaft from turning, but I would recommend you engage the kill circuit on the ignition (or remove the plug wires) for safety purposes just in case the motor rotates when you test the prop rotation (unlikely, yet plausible).

Re: I need some input. Merc 115 lower unit.

Thanks, I think the issue Im having is because I dont have it on the motor and I dont have a water pump installed on it yet so it spins freely

Re: I need some input. Merc 115 lower unit.

Yup... just hold that driveshaft from turning, and I think you'll find it will ratchet in forward as you expected.

The reason they ratchet in forward is in the event that you kill your ignition while at speed, the water wants to keep turning the prop (flow/drag) yet the driveshaft (motor) is stationary. This way you won't end up pressed against the windscreen as if a big water parking brake was applied if you motor stalls out while on plane. In that situation the prop simply 'freewheels' propelled by the water flow, and ratchets over the ramped clutch ears accordingly until you come to rest. Reverse gear has square cut ears to the clutch, and does not ratchet.

Re: I need some input. Merc 115 lower unit.

Thanks again AMD!

Re: I need some input. Merc 115 lower unit.

Hey AMD I got the (new to me ) used lower unit installed works great. Thanks for the quick input.

Re: I need some input. Merc 115 lower unit.

Glad to hear it worked out okay for you.

Pay it forward.


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