Mercruiser 120 not shifting into forward OR reverse after gear oil change

corinne

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Jul 27, 2015
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Hello and thank you for taking the time to read this. My husband and I are new boat owners. We have a 1972 StarCraft with a Mercruiser 120 I/O. We were out enjoying our boat one day and the engine started making a clunking noise. We stopped and rowed into shore. We figured it was the lower unit gear oil that was the problem and it was... chunky and gross. We refilled her, started the engine and she ran great! However, it does not shift into forward or reverse now! It just glides from front to back easily, but does nothing. Any ideas?
 

Fun Times

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May 16, 2009
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Hi there, welcome to iboats!:) I went ahead and moved your topic/question down into the Mercruiser I/O & Inboard Engines & Outdrives forum vs the Mercury & Mariner Outboards in hopes to try and help you with your situation better.:)

By chance when you drained the drive oil, did you happen to notice any metal shavings in the oil?

Did the drain plug have a magnet that collected any metal shavings?

With the engine off, Have you put the shifter into forward gear to see if the propeller will (by hand) turn/click in one direction and lock up in the opposite direction. Then you should notice the opposite turning & clicking direction in reverse gear.
 

corinne

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Jul 27, 2015
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Hi and thank you! There were no metal shavings in the oil, thank goodness! We have not tried to spin the propeller, however, my husband did notice that when we put it into forward gear with the engine off the shift cable wasn't moving properly and in reverse it would move a little then stop. Not sure if that's helpful, but we will try to spin the prop and I will let you know the results. Thanks again for your help!
 
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Mar 27, 2010
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Sounds like you possibly have a broken shift cable, there are two.

One cable connects from the shifter to the engine shift plate. The 2nd cable connects from the same shift plate to the outdrive.

Looking at the shift plate on the engine.. where the shift cables connect to, when shifting the remote shifter you should see the engine end of the cable respond to the shifter being moved. (will take two people)

If not, I would remove the forward shift cable off the engine plate (from the shifter) without changing the adjustment.

Try shifting again at the shifter see if the engine moves..... it should.

Try pushing and pulling (with your hand) on the shift plate to push and pull the other cable which runs to the drive. While the engine is off, check the prop to see if it goes thru the gears.

Pushing fully on the cable engages forward (prop will lock in CCW and ratchet CW)

Pulling full engages reverse (prop will lock CW and ratchet CCW , and in the middle is neutral.

Let us know what you find....
 
Last edited:

stonyloam

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Mar 13, 2009
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5,827
Time to learn how to pull the outdrive. If the oil was that bad you can bet the impeller (in the outdrive waterpump) needs to be changed and the u-joints and gimbal bearing and driveshaft need to be lubed. With the outdrive off you can check the shift lever. BTW how much oil came out of the outdrive? Should have been about a quart and a half.
 

corinne

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Jul 27, 2015
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Thanks for all the great advice! We will check into it this weekend and I will report back. Thanks again!
 

corinne

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Jul 27, 2015
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Well the prop is spinning and locking properly when using the shifter. We tried to do it by hand and the prop spun freely both ways. Not sure if we did that right though.
 

biggjimm

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Jul 15, 2015
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403
If the prop is locking up & ratcheting accordingly like Eric explained above with the engine off by working the shifter control in the normal manner, there shouldn't be anything that would make it not work while the engine is running I wouldn't think. I'm no expert but kinda thinking out loud here. Is the shifter gliding from front to back easily like it's not connected to anything? If so, I don't see how it could work properly with the engine off & not while it's running? Something sounds fishy with that???
 
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