notsofast

Came across this info on drivetrain.com.
It seems to describe what I have been observing with my problem/vibration.

[ VIBRATION-RELATED PROBLEMS

Vibration is a driveshaft problem that can either transverse or torsional.

Transverse vibration is the result of unbalance acting on the supporting shafts as the driveshaft rotates. When a part having an out-of-balance, or heavy side, is rotated an unbalanced force is created that increases with the square of the speed. The faster the shaft turns, the greater the unbalance force acting on the shaft.

The force produced by this out of balance condition tends to bend the supporting members. As the supporting members have a natural frequency of vibration similar to a swinging pendulum, a violent vibration may exist at certain periods when the speed of rotation and the natural frequency of supports coincide.

Each end of the shaft must be balanced individually as each support is responsive to an out of balance condition in portion of the shaft it supports. Out-of-balance affects operating conditions only when rotating.

Transverse vibration caused by a driveshaft out-of balance will usually emit sound waves that you can hear and mechanical shaking that you can feel. The force from out-of-balance increases with speed, not torque load. The driveshaft speed is determined by vehicle speed and the vibration is demonstrated best by road testing the vehicle to operating speed, disengaging engine, and checking vibration while coasting with engine noise eliminated.]

Anyone care to translate?

notsofast

Seems that the aluminum DS was out of balance. It is out, OEM shaft back in, vibration is now gone. Pinion angle was set with adjustable UCA, so I don't think that was the problem.
There is still a noticeable increase in driveline noise compared to before DS install, even with OEM shaft now back in. Not sure why this would be.

2010V6Stang

Bad install?

notsofast

Don't think so. Installer is an acknowledged expert Mustang tuner in our region and he's previously done work for me and others I know - very high quality. He has done other aluminum DS installs, also. I would definitely go back to him a again.

moosestang

I think, if you want an aftermarket drive shaft, you should install it yourself. I also think you should never lump mods together like you did.

First thing I would do is disconnect one end of the driveshaft and turn it 90 degrees, but that is usually for vibrations over 70mph.

notsofast

Thanks, but I don't find your comments to be particularly helpful. Your suggestion was tried but without effect.

shaftmasters

Even though this wasn't one of our driveshafts I would like to try and be of some help.
since we have sold hundreds of these aluminum driveshafts I can offer some of our experiences with customers who have done similar mods at the same time and are searching for answers to their harmonic vibrations. The only times that we have had reported problems with one of our driveshafts is when either suspension mods or a ratio change has been done at the same time. While it is time saving to do multiple mods at the same time it makes it harder to pinpoint just which one could be the source of the problem. Since you are still experiencing harmonics even with the OEM shaft reinstalled tells me that either the LCA's or the gear install is the problem. Rigid/ racing type suspension mods can cause harmonic issues especially when used with an aluminum driveshaft. The OEM driveshaft has a rubber sound deadening element inside that will mask harmonic vibrations. If the pinion bearing preload wasn't properly adjusted during the gear install this also could be causing your harmonics even after the OEM driveshaft was reinstalled. I hope that this is of some help.

notsofast

Shaftmasters,
Thanks for your help and advice. I had an adjustable upper control arm placed - the LCAs are the same (Metcos placed 2 years ago). It looks like the bushing in the UCA is a rubber/plastic compound, not metal - but I guess this could be part of the problem. The pinion gear and bearing were replaced as the aluminum DS damaged them. Thanks again - I'll post again when I know more.

2006gtmike

My driveshaft has made a loud rotational noise right around the 80 MPH mark only. The sound goes away when I speed up or slow down. It it is fine otherwise.

My installer told me it's my Steeda Adjustable Comp/Street Upper Control Arm kit with heavy duty mount.

Whether that is true or not, who knows!

It's been like that for 2 years. I'd like it resolved but no one has been able to.

Diabolical!

It sounds like the installer did not torque the pinion nut properly. A bad driveshaft should have no ill effect on a pinion gear.