Another "G" bites the dust... (broken shaft)

[formulaben]

They were 454s and darn big props...either way, the driveshaft can only "see" so much torque, which is limited by engine output, not raised by gearing.

Uh, you sure about that? The entire purpose of a gearbox or transfer case is to exchange RPM for torque.

[WheelerWake]

Uh, you sure about that? The entire purpose of a gearbox or transfer case is to exchange RPM for torque.

Right, if you have a 2:1 trans you get 2x the torque at the prop, but 1/2 the RPM. Horsepower stays the same. This is of course minus friction losses.

This is exactly how the trans or rear axle in a car multiplies torque.

[justgary]

Anybody got a photo of one of the broken shafts? The key way should have a generous corner radius in the bottom. If not, stress will focus at the sharp corner, causing a crack which will become catastrophic.

[isellacuras]

I think I remember reading something about the lateral forces doing the damage to the g shafts. Is that still thought to be the case, or do they think it's more of the rotation forces that are sheering them?

[nyryan2001]

Isell, general consensus is that it's a weak shaft materials or a machining issue with the key slot. At a .01%ish failure rate, it'd be hard to say it's a design problem. Those that break do it early between 20-60hrs. For those replaced, none have broke twice. Again, suggests a faulty shaft problem.

[85 Barefoot]

Isell, general consensus is that it's a weak shaft materials or a machining issue with the key slot. At a .01%ish failure rate, it'd be hard to say it's a design problem. Those that break do it early between 20-60hrs. For those replaced, none have broke twice. Again, suggests a faulty shaft problem.

Ryan by your own numbers there are 2600 G's and 25 failures, that's a 1% failure rate not .01%.

Edited September 2, 2014 by 85 Barefoot

[85 Barefoot]

Anybody got a photo of one of the broken shafts? The key way should have a generous corner radius in the bottom. If not, stress will focus at the sharp corner, causing a crack which will become catastrophic.

there's tons online

[nyryan2001]

yep my bad.

[Nitrousbird]

Isell, general consensus is that it's a weak shaft materials or a machining issue with the key slot. At a .01%ish failure rate, it'd be hard to say it's a design problem. Those that break do it early between 20-60hrs. For those replaced, none have broke twice. Again, suggests a faulty shaft problem.

Your percentage could only works if you compare the number of broken shafts posted online vs. the number of G owners posting online. I bet there have been more shafts broken from those that don't post on the forums than those that do, so we can't compare online mentions to overall sales and get an accurate number (and I'm sure Nautique isn't exactly sharing the number of shaft warranty claims with anyone as that isn't a smart business move).

Regardless, the failure rate is way more than .01%. That would be 1 in 10,000. I'm pretty certain they have not sold anywhere near 10,000 G's yet have had more than 1 broken shaft. Even comparing total sales to those shafts shown broken online, the percentage is likely well above 1%. I'm not saying it is a huge number, but the percentage is higher than you are letting on.

[nyryan2001]

Nitrous, yep .01 or 1%, mis-stated above.

[jk13]

BTW someone on TT may have broken one on an X46 w/ 7.4l and 10 hours.

First post coming in hot and no follow up:

http://www.mastercraft.com/teamtalk/showthread.php?t=63537

[Smokinjo]

A couple broken on 14 model MBs as well.

[nyryan2001]

BTW someone on TT may have broken one on an X46 w/ 7.4l and 10 hours.

First post coming in hot and no follow up:

http://www.mastercraft.com/teamtalk/showthread.php?t=63537

at 10hrs, another one early on

[Fman]

My friends 2014 MB is being finished up today for a drive shaft repair. I will find out more details this afternoon when we pick up his boat. We're leaving for Powell Thursday morning, so we are definitely lake testing this evening. I am wondering if it's anything related to the failures on the G. His boat has the 410. When I talked to him on phone last week he mentioned it was because the motor mounts wearing out and drive shaft becoming out of alignment, therefore damaging drive shaft components. He had to get towed in a couple weeks ago because of this. His dealer mentioned they have had six failures exactly like this on 14 MB's.

[wakeboarder3780]

I think that sounds like reasonable data. I doubt boat manufacturers make their own prop shafts in-house. There has to be a central supplier.

This reminds me a lot of all the circuit boards having issues about 5 or 6 years ago. Everyone was having failing video cards, motherboards, the occurrences were somewhat often, but not known to a specific brand. It ended up being that a Taiwanese company was selling the most cost effective (cheapest) capacitors and so lots of companies were buying them up and using them on their circuit boards. Turns out their capacitors were so cheap because the company was taking shortcuts http://en.wikipedia.org/wiki/Capacitor_plague

I wonder if whoever is supplying these shafts are taking some "cost savings" shortcuts these days too. It would make sense given the problem is happening at the same general time frame but is not brand specific. Just a thought. Even then it could be someone supplying materials to the shaft manufacturer.

Edited September 2, 2014 by wakeboarder3780

[nyryan2001]

My friends 2014 MB is being finished up today for a drive shaft repair. I will find out more details this afternoon when we pick up his boat. We're leaving for Powell Thursday morning, so we are definitely lake testing this evening. I am wondering if it's anything related to the failures on the G. His boat has the 410. When I talked to him on phone last week he mentioned it was because the motor mounts wearing out and drive shaft becoming out of alignment, therefore damaging drive shaft components. He had to get towed in a couple weeks ago because of this. His dealer mentioned they have had six failures exactly like this on 14 MB's.

Fman- how many hours on his 2014 when it broke? between 20 and 60?

Seems that engine misalingment would eat at the tranny and Vdrive bearings....versus cause a shaft to snap behind the prop shrut.

[Fman]

He said drive shaft broke, he has 200 hours on the boat. It might be something totally different, but very strange dealer has repaired six other boats this season. I will find out more this afternoon...

[justgary]

there's tons online

Well, thanks for reposting none of them here. I looked and couldn't see any of them. I'm not going to join another site just to look at one picture.

[isellacuras]

There's this thread in TMC: http://www.themalibucrew.com/forums/index.php?/topic/50365-another-broken-g23-drive-shaft/

Found by a quick google image search

Edited September 2, 2014 by isellacuras

[85 Barefoot]

Well, thanks for reposting none of them here. I looked and couldn't see any of them. I'm not going to join another site just to look at one picture.

1) I'm sorry about that, I didn't realize advising there are pictures online was an inadequate response. So, I went to google for you, typed in "pictures of G23 driveshaft break" and got the following link w multiple pictures as well as links to other sites discussing the issue with pictures:

https://www.google.com/?gws_rd=ssl#q=pictures+of+G23+driveshaft+break

2) I'm sorry you couldn't find any on your own.

3) No need to join any other site for content. Most sites dont require a membership for content.

[justgary]

Sorry to sound cranky. What I should have specified is that I'd like to see a close up of a broken shaft, not something from 30 feet away.

By the way, your link has multiple pictures, but only one shows a drive shaft (from 30 feet away). Certainly not "tons online."

[brad72]

Gets me thinking seeing them snap just after the bush and at the end of the keyway there there could be a few things in play. With an inboard shaft being on a angle the prop thrust is always downwards and therefore will be trying to push the rear of the boat out of the water and the bow down. With all the ballast and aggressive props these new boats have how much extra force is this putting on the shaft given the boats are not designed to lift and level out, but always run on an angle to create a monster wake? Also given the relatively slow speeds that these boats travel is the bushing getting hot because of the added friction due to the high loads in play causing heat and therefore hardening. I guess the only way to test this is do a run, switch off and feel the shaft. It is obvious these shafts are failing from plastic deformation or the key is being cut without any relief on the corners as Just Gary eluded to earlier.

Would still love to know what grade stainless they are using on the G's shafts

.

Edited September 2, 2014 by brad72