Group S Alfetta GT - Blown Donut...

[Paul Newby]

Ok Alfa punters, lets get a real NSW post happening here, not another announcemnet from quattrokid... 

Below are some of photos of my Group S Alfetta GT after the front donut let go at Bathurst earlier this month.

[Paul Newby]

Mmm, looks like I posted this before I had a chance to explain myself....

It happened along Pit Straight in my first race - changing up from 2nd to 3rd at about 7200rpm. When I released the clutch it went bang.

Luckily it didn't come through the floor and hit me. Also lucky no one was following me closely. The engine mount part of the bell housing ended up on the track on the racing line... 

Oh and a few other things I should mention:

1. The front donut was a year old. It had done 8 track days prior to its failure
2. The propshaft had been professionally balanced
3. I didn't over-rev the engine (limiter is at 7500 and I wasn't bouncing it off the limiter down Con Rod Straight
4. I didn't miss a gearshift
5. There was no vibration before it went bang...

But we also know that:

6. We had spaced the front donut with two washers so that the rear donut was not stretched...
7. It appears that the centre bearing may have been 3 - 4 mm out of alignment (the locating holes are elongated)
8. I have a button clutch and lightened gear set - so gearchanges are fast, but not to the extent of beating synchros...

Here are a couple more photos:

[Mat Francis]

wow. that is hugely impressive, for all the wrong reasons.

hmm, i have washers in my drifeshaft  but i only put one with each donut so as to spread the load evenly. and it all seemed to line up beautifully. i hope it wasn't the washers that caused it.

condolences and best of luck getting it all fixed

[Sheldon McIntosh]

There's a front donut?

[Paul Gulliver]

Photo's like that remind you of the old chain driven Citron's. A bit of an over rev and the chain could come through the floor boards and rip you laughing gear off. The stuff of nightmares.

I saw this thread on Alfa BB about donuts exploding. A very simple and neat solution.

http://www.alfabb.com/bb/forums/transmissions/149249-giubo-savers-simple-but-elegent-solution-donut-problem.html

Perhaps this is something that a Vin Sharp may be albe to fabricate???

[Jekyll and Hyde]

Photo's like that remind you of the old chain driven Citron's. A bit of an over rev and the chain could come through the floor boards and rip you laughing gear off. The stuff of nightmares.

I saw this thread on Alfa BB about donuts exploding. A very simple and neat solution.

http://www.alfabb.com/bb/forums/transmissions/149249-giubo-savers-simple-but-elegent-solution-donut-problem.html

Perhaps this is something that a Vin Sharp may be able to fabricate???

I don't know that this would do particularly much for the front and rear donuts of an alfetta/90 etc, as when you look at one, three of the bolts are already joined together by the metal carcass that the rubber is bonded to - unlike the centre donuts, or 105 donuts.  And I suspect if you used just one plate to tie the other 3 bolts together, it may foul on the existing metal frame of the donut, and cause a vibration....

[MD]

Paul, agree with J&H regarding the function of that triangular plate. You are still dependant upon the bond of the rubber to hold to the metal under duress and that's when it fails.

There are some "cans" in use that work to contain the "bulge" of the rubber under load and restrict its movement so that it keeps its integrity. (see photo) There are also alternative couplings that can also be used (see 2nd photo). Ideally, each of the couplings should have one fitted.

Finally, its is possible to make a conversion plate system to the flywheel and shaft to modify the donut PCD for a more contemporary BMW/Mercedes coupling which are much more robust.These use 12mm mounting bolts as opposed to the Alfa's 10mm.

[Paul Gulliver]

MD

Great alternative. I'm not a Group S racer (but fan of the concept & love watching & listening),  would you get that through scrutineering

[MD]

Paul,

I couldn't honestly say. However authenticity is one thing and safety is another. Seems to me that common sense and safety should prevail. The reason I say that is because genuine replacement stocks are getting pretty old and the rubbers are deteriorating along the way. After market versions don't seem to be as well made as the originals. Consequently, you install what you beleive to be a good  and genuine product only to put your nuts on the line ! 

One memorable day, I blew a segment out of all three donuts at the same time. It was like machine gun fire and there was rubber all over the place.

For racing applications it is possible to use three universal joints or CV's or a combination of the two. The only drawback is the serious hammering noise below 1800rpm but otherwise they work fine. To get rid of the noise requires just one rubber isolation donut-preferably at the front. If you are going to modify the shaft to that extent, then you would also use a contemporay donut to go with it and thereby fix the initial problem also.

...and if you ever find a crowd that makes carbon fibre shafts in Oz, let me know . 

[k76]

First of all I'm glad the damage was limited to the car and not the driver! The bellhousing looks like it took the brunt of the force, and may have saved your legs there Paul. With all the carnage at the driveshaft there is comparatively very little damage to the transmission tunnel. At least compared to the 105 on AlfaBB.

What did you do immediately after it happened? Hit the clutch, or lock the brakes up? I'd be a bit worried about the forward end of the driveshaft punching through the tunnel and making a big arc inside the cabin. Hopefully it spins too fast to do that...


Kris

[alfagtv58]

Yeah....bad luck Paul.  I was in that race, I come around Murrays corner and spotted a broken bit lying on the track and thought "wonder where and who that came from".....then I saw #31 sitting against the fence and thought "OH NO  " .  I must admit that it wasnt as bad as I had first imagined, I thought that part initially was a front wishbone as I spotted it for that half a second.

Hope you have her all patched up soon.

[Paul Newby]

Hi Kris,

Can't really remember too much about what happened apart from trying to get off the track. Obviously I hit the brakes but I don't think I declutched, probably because at first I wasn't sure what happened. If I declutched it may have stopped the propshaft spinning but then my foot would have been in a vulnerable position.

Certainly hitting the kill switch did nothing... 

The impact of the bang cracked the windscreen and also dislodged the throttle linkage rod.

Yes Phil, given what happened it could have been a lot worse. As I've discovered before ( ) these Alfettas have strong bodyshells. Probably why they are so heavy...

Paul

[Sheldon McIntosh]

The impact of the bang cracked the windscreen

[John A Pucak]

Hi Paul, maybe you should keep all the broken bits and build a shrine ( offerings to the Gods of speed),
just like Burt Munroe in the Worlds Fastest Indian.
Hollywood

[Paul Newby]

Thanks Hollywood.

Yep I'll keep the bits for posterity.

Like your conrod and Billy's flywheel ...