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My bet goes to the flexing in the guibo due to the engine pulling straight when torque is applied. Only the front guibo endures this much movement, the other ones take much less stress.

I thinks its the costant flexing at high rpm that causes the disintergration . The cages have a 4mm gap with a flat edge so the metal will chafe against each other . Never ever seen a coupling failure with a cage amongst all the 24v motors in SA and we were using 20 year old original couplings . Cages do take a beating . The marks on the cage show about 25mm distortion of coupling . The IMSA 75 turbo that came to SA had a single piece carbon prop with a universal on rear by gearbox and rubber coupling/guibo with a cage on front . That was over 400hp .

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Kevin, did I read that right 25mm? I what direction is this movement?

Kev,

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Is the movement really upto 25mm or almost 1" ? That's a lot!

Yes, that's no BS. I recently built a 24v and put on it a rwd flywheel from a gtv6. The 3 stud bosses are HALF EATEN on one side due to the repeated impact of the 3 driveshaft bolts/nuts. But strangely enough, it is NOT the side of rotation! I wonder under what conditions this contact occurred. If you look at the angle the donut has to distort for this to happen its unbelievable! Its a miracle they last as long! Here's a pic of the flywheel, check out the boss, with wear almost down to the bolt! All 3 are the same.

Jim K.

Did the owner perhaps not notice the odd vibration in the driveshaft from a failed donut and kept on driving?

I've had a completely destroyed donut once on a 75 TS that you didn't really notice. No vibration while driving steady.

A lot of drag race style starts? I've never seen these happen. I seldom ever do an aggressive start.

It's about 18-20mm movement as I could see chips on the powder coating where the nut catches the cage . We also had not standing starts so it was probably from the second gear hairpin bend on our track .
The non coated cage shows more aggressive marks and their was no coupling failure at all . Coupling still looked very good .

That tells me that the cage will lengthen the life of the flywheel bosses, studs and the guibo! One of the problem with an exploding guibo is the stud may or may not be parallel. anymore.

The wear shows how much the disc twists which is what it is designed to do. My bet is that the most damage (wear) to the discs occurs from radial growth from high rpm centrifugal forces. How much clearance is there between the cage and the outer part of the flex disc?

Since 1994 (~60K miles) I am on the 2nd front disc with a 300 ft/lb motor but I keep revs around 6500. This experience is what leads me to believe its centrifugal forces not rotational torque that does the damage.

Any first hand experience with the aluminum discs with the rubber grommets seen on the Biscione site some years back?

-Brian

Hi Brian
It's a tight fit . You have to really use a bit of hand strength to squease it into cage . What you actually are doing is making the guibo/ coupling round by fitting it in cage .
Here's one on my other car . ( the Gold member phase )
If you want to adjust the limit of movent you can . You can't destroy a coupling with these . Practically impossible .

Kevin, That settles it in my mind. It is an exoskeleton for the flex disc.

That gold paint... must be worth 5-10 BHP huh!

A ton of cars use these hardy joints. All of them fail. Mercedes, BMW and even the Corvette which has them in a torque tube so deflection is not an issue. At any rate, non of them have a cage solution like I see with the Alfas. Interesting I think. The Alfa style discs are also about twice the thickness.

-Brian

But on the Mercedes, bmw and corvette they're perfect in line and don't twist...

The alfa v6 lies crooked in the car. It's off centre by something like 10 degrees or so. So every turn of the propshaft twists the front guibo.

Putting the engine in straight will require new enginemounts and a new rear mount. And probably a harder material for it as well. That will keep the engine from twisting the guibo.

I tried this once with a v6 in a giulietta. Used front part from an alfa and the rest was a bmw propshaft made to fit. So alfa guibo up front, bmw uj in the middle and bmw cv joint in the rear. Worked quite well but unfortunately car was stripped for parts and not driven much before that. How it behaved at higher speeds is unknown due to that. I'll see if i can find some pics on it.

Giuliettaevo2 wrote:But on the Mercedes, bmw and corvette they're perfect in line and don't twist...

The alfa v6 lies crooked in the car. It's off centre by something like 10 degrees or so. So every turn of the propshaft twists the front guibo.

Putting the engine in straight will require new enginemounts and a new rear mount. And probably a harder material for it as well. That will keep the engine from twisting the guibo.

I tried this once with a v6 in a giulietta. Used front part from an alfa and the rest was a bmw propshaft made to fit. So alfa guibo up front, bmw uj in the middle and bmw cv joint in the rear. Worked quite well but unfortunately car was stripped for parts and not driven much before that. How it behaved at higher speeds is unknown due to that. I'll see if i can find some pics on it.

Only the Vette are they "aligned", not so with the BMW or Merc. Chevy has many failures, check out the forums. I don't think alignment fore to aft is the issue, it's the centrifugal forces that literally rip the component apart which is exactly the protection the cage provides. The disc is not aligned with the cage nor does the cage prevent the disc from rotating (stretching) in a circular manner as evidenced by the wear marks in the oval sections. The ovals are there to allow this motion but in Kevin's example the motor had enough power to stretch it even more.

Lastly, Chevy has found a solution to exploding discs by making them out of Aluminum with rubber inserts like... wait for it... the Alfa racers did from the Biscione site.

-Brian

Toyota also did that in the 1991 Previa/Estima/Tarago

https://www.youtube.com/watch?v=hTYgN44ah0k

Beninca and Jemison said it's possible to align the box to the engine better.

Could be a combination of both. High RPM will definitely increase the centrifugal and mis-alignment will also speed up failure.

I talked to Rob at Centerline in CO and he said Centerline has found a better supplier for the donuts.