Broken output shaft & coupler
 

Hello again everyone. I having a problem with breaking the Mercruiser output shaft 93906A 2. I need something
stronger. The first one I replaced was twisted and the 2nd was just a few days ago and it completely broke and
spun the coupler. So my question is does anyone know of a stronger shaft for sale or a shop that can make one thatI'm not going to snap off?

Thanks

That shaft is not usually a weak link. I would think you'd be breaking vertical shafts first.
I think you might have an alignment issue.

I bet that your engine is moving around - That is the only way I see you breaking a shaft and blowing the coupling.

I've had a prop shaft and a vertical shaft break....never have broke an input shaft....neither of these are near a robust as the input shaft.....like what everyone else is saying, you have something wrong alignment wise

I have IMCO SCX 4's on the boat I don't think they would break before that stock output shaft. I also have front and rear motor plates so I can't imagine it's moving around but I had not thought to check that. As far as alignment I wouldn't think it could be off that much, the output shaft bolts to a flange with a universal joint. If the alignment was off that bad I would think the universal joint on either end of the driveshaft would break. I really think I'm just over powering the stock shaft.

How much power?

It right at 1,000hp per engine.

Where is the shaft breaking? I also believe it is an alignment issue. If it was mine that is what I would check first.

With a 1000hp and running SCX's, the input shaft may have well become the weak link.

The shaft is breaking in the splines outside the coupler.

This is the reason I don't think it's an alignment issue, and please let me know if I'm not looking at this the right way. On the back of the bell housing is a bearing that this shaft rides in, that is bolted to the engine. The driveshaft hooks to that output shaft with a universal joint. It is not mounted to the boat but to the motor so if the motor moves it will move with the motors. On the other end of the driveshaft is another universal joint and a bearing that the input shaft from the drive goes into. So my thoughts are with the 2 universal joints in between the motor and the drive even if the alignment was off a little it wouldn't matter.
Thank you for your input.