I've had quite a few driveshafts made over the years, but about 10 years ago I ran into a cyclic vibration in the driveline at 65mph of a car I'd built for a customer and after eliminating everything, including having the driveshaft rebalanced locally, I decided to buy a driveshaft from Dynatech in Michigan..........

Dynatech spins their driveshafts to 6,000rpm (In the Tulsa area, the fastest that any driveshaft place can spin balance a driveshaft to is 2,500rpm)......This car was instantly as smooth as glass.....The Dynatech driveshaft felt obviously heavier than the shaft made locally, the U-joints were of obvious higher quality and the yoke was of obvious higher quality.......

Since then, I've bought numerous driveshafts from them and every car has been as smooth as glass.....I've even fixed two cars for people, that had cyclic drivetrain vibrations that they couldn't figure out, by installing Dynatech's shafts and the difference was night and day........

Last week, I needed another driveshaft for a customer's car and I tried to get ahold of Dynatech and after two days of calling and only receiving voice mail, leaving messages and no return call, I called a recommended driveshaft company that specializes in "race driveshafts".......

I was curious as to how high they spin their shafts and the guy tells me that they spin their shafts to 500rpm........I asked what he thought about spinning shafts to 6,000rpm and he laughed and said that's not worth anything.....he said it's just a "wive's tale" and he actually got slightly upset and frustrated about the topic.....told me how long he'd been building driveshafts and how spinning them faster than 500rpm was a waste........

Before that conversation, my thought was that the driveshafts in most cars now-a-days aren't spinning any faster than 2,000-2,500rpm on the highway so as long as they're balanced at that speed, they're fine.....The cars I work on typically have lower gears and are drag raced and cross the finish line between 6,000 and 7,000rpm so the driveshaft is spinning that fast and they need to be spun that fast.......but now, I'm not so sure............

After thinking about it, tires aren't spun to highway speeds to be balanced.........Crankshafts aren't spun to engine speeds to be balanced......Why do driveshafts need to be spun to 6,000rpm????

So, my questions are;

Is there any merit to spinning driveshafts at a faster speed, or is that a gimmick???

Were my driveshafts from Dynatech better because of the higher quality parts????

Is the balancing machine at my local place that jacked up???

There is a critical speed for any shaft, tube or solid, when exceeded, can do strange things to a shaft. Too many variables but length, diameter, tube thickness would be three of the most important, probably why the Dynatech shaft was heavier but worked for you. I found out the hard way several years ago that even a 32" 1 3/8th solid shaft has its rpm limits. I'm not sure this link below is all inclusive but will maybe give you a pretty good baseline.

http://www2.dana.com/expert/wc.dll?hvtss~decrits~warn1

I just let Dynotech make mine.. they have done 6
of them for my own junk... most cases a item that
spins goes through a "Order" frequency and in most
cases its a X factor.. I've watched a ton of stuff
on a strobe light to get the frequency .. then when
you double it, it comes back in again... like a set
of tires.. they may be out of balance at 60mph and
again at 120mph