1975 Mercury 850 stopped driving forward

[tgodliquor]

OK, the other day I was in the bay going out to get my crab pots when my motor felt like it popped out of gear. I didn't try reverse as I was panicked to get the kicker motor started. I did mess around with the motor and this is what I can tell you. I hear it go in to gear even though it will not propell the boat forward. It appears that there is less water coming from the motor, but the motor sounds great and it running excellent. On the trailer I put the motor in gear and can spin the prop forward by hand (with a clicking sound) but it will not go backwards while it is in forward gear. With the motor in reverse the prop will not spin forward or backwards by hand. Is there a shear pin somewhere that may have gone? Did the lower end go out? Any info may or may not help my anxiety. Thanks for the help.


Todd Godfrey

 

[oldman570]

Re: 1975 Mercury 850 stopped driving forward

It would be best to pull the LU and see it the DS broke somewhere. With the motor not running it might be enought pressure on the brake yet to not be able to spin the prop. JMO
Oldman570

 

[Maxz695]

Re: 1975 Mercury 850 stopped driving forward

On the trailer I put the motor in gear and can spin the prop forward by hand (with a clicking sound) but it will not go backwards while it is in forward gear. With the motor in reverse the prop will not spin forward or backwards by hand. This is proper shift description. The prop should click in one direction and lock in the other in forwards spin freely both ways in Nuetral and lock both ways in reverse. turn the flywheel in fowards and see if the prop moves. Is it does it,s not the driveshaft and more than likely you hit something and spun the prop

 

[Texasmark]

Re: 1975 Mercury 850 stopped driving forward

A spun prop is a possibility. Now that you know that the engine shifter/drive is functioning properly, take the prop off and scribe a line from the innermost hole (spline) out across the hub....includes the material the prop is made of but you don't need to go all the way past the exhaust openings to the outer shell of the prop.

Take the boat out and hit WOT several times and as convenient, remove the prop and check your scribe line. If it is no longer lined up you have a spun hub and need a prop shop to install a new one or get another prop.

The engine has a lot more torque than you have with your hand so while you were checking the operation of your shifting system, just because you were unable to turn the prop doesn't mean that it isn't spun. Check it.

On the water pump outlet seeming reduced, this could be a normal reaction as a result of your boat's speed. No ram water pickup.

Mark

 

[tgodliquor]

Re: 1975 Mercury 850 stopped driving forward

Thank you guys for getting back to me so quickly. I think you guys are right with the spun prop. I went back out and put the motor in reverse and I can actually spin the prop on the drive shaft. It's not free spinning, but with force I can get the prop to move and the shaft stays put. So not to get too technical what do I have to do from here? New prop shaft? New prop? Both? I've got a guy nearby that I can get used parts from but where would I get new? And where would I find a manual online? Thanks again for all your help!

 

[Maxz695]

Re: 1975 Mercury 850 stopped driving forward

Purchase a new prop of the same pitch and diamiter> Yea!!! them damn underwater lines on pots and stuck anchores reek havoke on a prop

 

[mercurymang]

Re: 1975 Mercury 850 stopped driving forward

sorry, I posted in the wrong thread.

 

[tgodliquor]

Re: 1975 Mercury 850 stopped driving forward

OK guys, finally took the time to remove the prop and the hub is bad. I need HELP finding the right hub to replace it. 1975 merc 850. There are a ton of them online and I just dont know which one I need. HELP! THANKS.

 

[merc850]

Re: 1975 Mercury 850 stopped driving forward

I usually take mine to a dealer who sends it to the "prop shop" for rehubbing - unless it is one of the new ones with the sleeve hub.

 

[dwco5051]

Re: 1975 Mercury 850 stopped driving forward

Purchase a new prop of the same pitch and diamiter> Yea!!! them damn underwater lines on pots and stuck anchores reek havoke on a prop

Look for numbers stamped on your present hub such as 19P x 13.5. If your present prop gives you the performance you like match the pitch and diameter when buying another one. If you don't need the motor right away send the old prop out and have it re-hubbed. Do both and you will have a spare for the next time you need one. I usually watch garage sales and craigs list for spare props for my boats and if the pitch and diameter are close I will pick a cheap one up for an extra spare. Never know when you may damage two in the same weekend and I least can still fish.

 

[Texasmark]

Re: 1975 Mercury 850 stopped driving forward

If all else fails go to a prop shop and tell them "I want one of these". They can put it on their instruments and determine d and p. Or if it's not all dinged up, rehub it for you . Course if they are having a prop sale it may be cheaper to buy a new one especially in alum.

Mark

 

[Yesterday]

Re: 1975 Mercury 850 stopped driving forward

You might also consider buying another, while haging this one re-hubbed. It's never unwise to carry a spare on board, with proper wrench to change it.