Merc 850 wont go into forward gear

[efdog]

So I was cruising along today when I heard a knocking sound coming from the outboard. Then a short while later there was a loud knock which seemed to come from the lower unit. I immediately put into neutral and tilted my engine up as it felt as though I had hit something. The prop was fine so I lowered. I went to go back into gear again and i did, however prop wasnt spinning fast. The rpm's would go up as usual, just no speed. I put it back into neutral, and the next time I attempted to go into gear...nothing...I tried a few times and it will only rev up the rpm's, but will not go forward. Reverse is normal and that is how I had to get back to shore. I would assume I have a problem with either the lower unit or shift cable? Anything I can check to troubleshoot? Any help is greatly appreciated.

 

[Chris1956]

Re: Merc 850 wont go into forward gear

Disconnect the shift cable at the motor. Now move the shift slide forward and see if you get a solid forward.

Check gear oil for quality.

 

[efdog]

Re: Merc 850 wont go into forward gear

Finally got a chance today to have a look...and yes it gets a good forward. I havent checked the gear oil before. Is this the screw below the "flush" screw? If so, it's stripped from the previous owner. If the gears are the problem, are they replaceable, or would I need a whole new lower unit?
Thanks for the help!

 

[Chris1956]

Re: Merc 850 wont go into forward gear

Use a cold chistle to tap the drain screw loose. Replace the gear lube and the drain screw.

Put the MerControl in neutral (throttle handle at noon position). Adjust the shift cable barrel nut to fit on the shift slide in neutral. Water test ot see if the gearcase is good.

Normally on those old motors, we just replace the gearcase with a used one.

 

[efdog]

Re: Merc 850 wont go into forward gear

Hey Chris, okay so I've removed the oil from the lower unit. It was jet black and seemed a bit milky to me as well. There were metal shavings on the magnetic drain screw as you can see from the photos. Not sure is this is normal or excessive. I did however notice that neither of the screws had a gasket seal. I'm assuming this is NOT normal. Should I pick some seals up? Thanks again!

 

[Chris1956]

Re: Merc 850 wont go into forward gear

Metal on drain plug doesn't look too bad. Clean off the metal shavings. Pick up some gaskets and a new plug, and pump 26 oz of fresh marine gear lube (any marine gear lube but type C), and fill it from the bottom. Did you adjust the shift cable as I described? If not, you should.

Run it for an hour or so and drain it and check for water. If you still have gear problems, it is likely time for a new gearcase.

 

[efdog]

Re: Merc 850 wont go into forward gear

I've got the oil replaced with some quicksilver gear lube, with some new gaskets and plug. Using muffs I've started it up, and notice that even in neutral the prop is moving very slowly, and I can hear a slight grinding from the lower unit. I did not adjust the shift cable. There are 2 cables going to the engine. Which one engages the gear?

 

[Chris1956]

Re: Merc 850 wont go into forward gear

The bottom cable is the shift cable

 

[efdog]

Re: Merc 850 wont go into forward gear

I did as you suggested. Probably incorrectly, however I did disconnect the shift cable, and set into neutral. No adjustment to the cable was necessary, as the cable and slide lined up perfectly when both set to neutral. I'm considering either taking it to a shop, or buying a service manual. I really dont want to drop a lot of $ into this old motor, but at the same time it was running great before this issue so I would hate to have to scrap it. Striper season is coming here in NB, and I cant miss that! Thanks for your help either way. I'm still a boating newbie and have learned a lot from this site!

 

[efdog]

Mercury 850 Gearcase Lower Unit

Mercury 850 Gearcase Lower Unit

How can I find out compatibility for a 850 lower unit? Do all merc 85 HP 850's use the same lower unit?

 

[Chris1956]

Re: Merc 850 wont go into forward gear

Gearcases from inline 4 and 6 cylinder motors from 1970s to mid 80s will fit. Gear ratio will be 2::1 or 2.3::1. Change prop pitch to 2" lower if you change gear ratios.