I would be surprised to hear a drive input shaft sheared off, it sees much less torque than the vert or prop shaft and has sorta a torsional action to it because of length, how much hp /tq do you have, what props?

I see you have 1000 hp, my 272 Baja had over 1000 hp and ft lbs of tq, one drive had stock std input shaft and ujoints, my other drive had xr input shaft and u joints, sheared plenty of vert shafts and prop shafts but input shafts still looked like new, I guess it could happen but again, I would be surprised, wondering if your running tall 5 blades that really stress it or something? Smitty

Am I correct to assume that this is the forward engine in a staggered application ?

Triple boat ? If so , same pitch on all props or higher on center eng ?

Yes you are correct.

1,000hp per motor, props are labed Herings 17/38. It's not the drive input shaft that I'm having a problem with my SCX drives are fine. It's staggered engine boat and it's the forward engine and it has a output shaft that goes in the coupler to a drive shaft then back to the input shaft from the drive ( SCX 4's )

Not a triple boat.

Props are 17/38 5 blade Herings that have been labed. I know I'm putting a lot of load on the shaft that's why I'm looking for a stranger one.

Try Denny's Drivshaft in Buffalo NY
He should be able to eliminate the weak link and help you find the next one 😉

Thank you I will look them up. I'm afraid of what the next weak link may be.