Any advantage to retaining the rubber donuts

[rgh0]

The diff crown wheel bolt failure is a fatigue failure and typically comes from the bolts tension being lost over time and then fatiguing due to the cyclic loads it experiences This has no strong relationship to donuts or CV or UJ output shaft design I think .

The use of rubber couplings in the rear prop shaft in many European cars relates to the best / cheapest way to connect a chassis mounted GB with a chassis mounted diff, that only experiences minor misalignment. I have them on my VW Touareg and sons Golf R32 to the rear diff on both these 4WD cars.

A dopting this design was a big leap of faith by Chapman and his designers based on using the same type of setup designed originally for small misalignments in industrial machinery and as used on a much less HP Hillman imp with less suspension travel and a combination of UJ and donut rather than 2 donuts. The brakes were forced outboard as if inboard the car could move significantly with the hand brake on with coupling wind up on a hill... embarrassing if parking close to a car in front or behind. In the end the deflections on the Elan suspension and torques are really to great for the design especially with more modern tyres grip.

As usual in engineering a whole bunch of compromises around cost versus performance made then and need to be considered now.

cheers
Rohan