Donut doubt

["Lee Scanlan" <Lee.Scanlan@domain.elided>]

I have recently replaced the rear donut on my Alfetta sedan after a complete 
segment flew off and the remaining item broke up with a big bang and 
discernable vibration.
Whilst fitting the new donut, obtained overnight from helpful Turin Imports 
of Adelaide, I noticed the rubber moving through a good bit of axial 
ditortion as the six fasteners were tightened. After all the nuts were tight 
the donut looked like a giant rubber wave washer, it's as though the rear 
end of the rear shaft was too far away from the gearbox/clutch input spider 
(three legged spider) and the rubber was being "pulled" to meet both faces. 
This helped to explain why the old one broke. Is this normal? The distortion 
could be a result of some angular displacement, on the vertical plane, 
between shaft and gearbox, very obvious on the bottom most segment, the part 
you can best see, gearbox mountings are good so I don't believe the 
transzxle is nose down.
I can't help but think this isn't the way it was meant to be, the coupling 
must be constantly changing shape, the other two aren't subject to this 
torture and is possibly why they have no cracks despite being the same age. 
In AD7/1078 Mike Grace researching a 105 driveline vibration received advise 
to shim the donut fasteners to relieve any tension in the rubber, if it were 
NOT an angled alignment problem this might work. Car runs fine but I'm 
wondering for how long. Does the rear donut normally fail soonest, can 
anyone offer any advise or comments please?
Lee Scanlan 
Perth W.Australia

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