Re: Bad vibrations

[PGAHOWELLS@domain.elided]

Hi Dean
Thanks for your note.
As you have an auto my guess is that the elastomer joint in the propshaft is 
not in quite such  a rigid state as when the car was new. 
This is a rubber ring between inner and outer propshaft tubes near the rear 
UJ.
Read an early road test and you will see even on some brand new cars this 
would give vibrations over 75 mph.
After many years of taking all the torque the rubber becomes a little 
stretched.
This means the shaft can go out of straight. Then it flutters at speed. Like 
a badly loaded spin drier. Sometimes it is worse than others depending on how 
the propshaft lay during the last parked period.  

Solution
Very difficult. I tried three different props before finding one that was not 
too bad. I am still working out how to deal with this problem. Another answer 
is to have a solid propshaft made up from the one you  have by having a new 
piece of tubing inserted and a special adapter to downsize to the rear UJ 
joint connection. I imagine the auto changes would be harsher going this 
route.
Possibly a polyurethane elastomer coupling could be introduced by someone but 
it doesn't exist yet and with more and more people converting to Manual boxes 
it looks an unlikely solution.
What can you think of? 
Regards
Peter H