[93formula]

i got a guy whos bent 2 drive shafts.

the car is a ls1 f body. he is the original owner, road races but doesnt drag race. the car is pretty much stock.

the first drive shaft bent with original suspension. at speeds of about 220-230 km/h. well some serious vibrations were met.

then it was replaced by a shop with a steel drive shaft for temporary use. tested it, ran fine for a bit at speeds of 220 km/h. then a short while later the vibrations came back.

went to the shop again, it was bent.

the only differenced between the two times was the second time he had some suspension mods done like new konis, relocation brackets, eibach pro kit, aluminum lcas.

now what the hell would cause two drive shafts to bend at speeds of over 220km/h???

[35th_Anniversary...]

the critical speed is actually the torsional or lateral resonant frequency. This is a factor of the stiffness and inertia of the shaft.
stresses and deflections are magnified when you are running at or near the resonant frequency. We do a lot of torsional analysis work here at work as we make products that are similar to engines with rotating & reciprocating parts. A torsional failure would have broken the shaft at a trademark 45 degree angle. IMO if it was a resonance problem it must be a lateral resonant frequency it was running at. Of course I can't say whether or not this is the actual failure mode.

If you ever see your mirrors vibrating when a bass note plays or at a certain engine RPM the mirror is vibrating in resonance. blow across a half empty coke bottle and yu are hearing a 1/4 wave resonance. Pluck a guitar string and it is vibrating in resonance.

With my experience working with the products at work I sometimes wonder how an engine in a car can rev from 800 to 6000 rpm without going through any resonances. (Maybe when I get bored I will do one) The torsional resonant frequency can't be too high with all the inertia in the system, counterweights, pistons, connecting rods. And when you have a low torsional resonant frequency you will have higher modes of vibration as well, so even if you are below 800 RPM on your first mode you still have to contend with yur 2nd, 3rd, 4th, etc. Plus in an engine you also have to worry about additional resonances from half orders.