'83 Johnson 50hp -- what would make a drive shaft snap in half?

[surftrish]

It's definately broke clean in half (right where it goes down into the lower unit). Everything else on motor seems to be working fine, didn't hit anything recently... the propeller just stopped turning one day. Took the lower unit off the other day and the drive shaft is in two pieces. I'm going to replace it but am wondering what could have caused the break? Just old age? That simple metal rod is expensive and I'd like to purchase just one.... Thanks for any help or insight.

 

[Solittle]

Re: '83 Johnson 50hp -- what would make a drive shaft snap in half?

What do you mean by "recently?" The only thing I can think of is a flaw was in the shaft when it was manufactured. You may have hit something sometime to aggrivate the flaw. Never heard of a shaft going like that.

 

[alcan]

Re: '83 Johnson 50hp -- what would make a drive shaft snap in half?

I don't know if this is your problem or not, besides what solittle said it could have too much load. I have lost driveshafts this way before. It dosen't have to be a one time deal. It can be accumelative over time. There is a lot of stress on that simple rod.

 

[surftrish]

Re: '83 Johnson 50hp -- what would make a drive shaft snap in half?

Thanks guys ... i've only had the boat for a year so am not sure what the previous owner put it through. I had to have the powerhead rebuilt immediately when I bought it. I run it in the intercoastal a lot so hit soft bottom sometimes but nothing dramatic or at high speeds. I'm going to shop around for a new part and go from there.

 

[clanton]

Re: '83 Johnson 50hp -- what would make a drive shaft snap in half?

Im not sure of year, but the driveshaft has changed over the years to solve this problem. One change was to make shaft larger, Some of the waterpump kits came with 2 different size impeller, to insure correct fit to the different size shafts. There is also OMC letter/bulletin changing the shimming specs. A good dealer will have this information, then you could decide to go new, or look for used shaft.

 

[Chinewalker]

Re: '83 Johnson 50hp -- what would make a drive shaft snap in half?

Often the driveshaft is the weakest part of the drivetrain. I've seen motors that have had a gear tooth let go and that broken piece gets caught between two other gears. The gears effectivley stop moving and something has to give. You've got the mass of the crankshaft and flywheel spinning up above and a dead stop down below. If the splines don't spin out, the shaft might break... When you take it apart to change the driveshaft, inspect the gears carefully...<br />- Scott