'76? Mercury 85hp o/b Lower Unit Problems

[fomoco-gnatsum]

Had the boat in the water for about 2 weeks worked great! (16' ThunderCraft Bowrider)Tubing and cruising etc. Has power tilt & trim. Now when I go to put it in Forward it revs up and makes a huge clunking sound shaking the transom back and forth. It will work in reverse! Any quick Ideas what may be causing this. Has a brand new prop and the lower unit was just replaced recently by the previous owner at a marina.

 

[sharkcat]

Re: '76? Mercury 85hp o/b Lower Unit Problems

I know Im repeating myself but GET A MANUAL .Pictures & diagrams are worth a thousand words.If you go to www.marinshopen.se click on modelguide youll be able to confirm the year of your engine(unless it was built in europe,australia or canada)Then you will be able to get the right MANUAL .Check that the gear cable is adjusted correctly ie.going into forward all the way.If this doesnt solve your problem & from what you have posted I dont think it will. .I would think the problem is the dogs on the gears are rounded & it is jumping in & out of gear.I once had this prob & it was caused by fitting a used centre section that had faulty top mounts & the shift shaft was binding.Good Luck

 

[blueboat1]

Re: '76? Mercury 85hp o/b Lower Unit Problems

I had a similar problem; it was a broken gear in the lower unit. It would shake because it would barely grab the top of the broken gear. I hope it's not that.

 

[maillon]

Re: '76? Mercury 85hp o/b Lower Unit Problems

I think the problem you are having is one of two potential problems. <br /><br />At first I was thinking that your linkage needed to be adjusted but this may be incorrect if it was shifting smoothly between forward and reverse when you first launched the boats two weeks ago.<br /><br />Therefore, I would blame the shift cable. Look closely at you shift cable. Especially at both ends where the cable plastic meets the metal ends. Is the plastic breaking off anywhere? If so then the cable will not be able move the full length of what is needed to shift the motor. Replace the cable.<br /> <br /><br />If the shift cable looks fine, then I think its inside the shift box. Inside the box this is diamond-shape piece of hardware that needs to be replaced. Inspection of this piece may look to be fine, but in reallity its worn and needs replacement.<br /><br />In either case, it sound like you shift box or cable is preventing you from fully engaging the motor.<br /><br />Take the cover off and watch how far the linkage travels when you shift it. It shoud be the same in both directions.<br /><br />I very much doubt it's your lower unit.