high speed vibration from driveline

Guys, I have had this issue for a long time but I think i finally found the source of of my vibration. The problem has been that around 80mph, i get some sort of vibration from the drive line of the car. In the process of trouble shooting, i have checked the runout and balance of everything and never found anything wrong. I have also tried 3 different drive shafts with no difference between any of them.

But one thing i overlooked was the angle the transmission was on. I found that my trans is on a 4.5° angle and the pinion was at 0°. I now know that both the trans and the pinion have to be on the same angle. But when I do this, my drive shaft runs at a 4° angle out of the pinion and this causes even more vibration. The recommended pinon angle is no more than 2°.

I am pretty confident that these angles are what have been causing the vibration. But, there doesn't seem to be away to fix this. With the car riding so low, I dont think its possible to to have the trans and pinion angles parallel without running the drive shaft at a 4° angle. This is even after i shimmed the rear of the trans as high as I can, its almost hitting the tunnel now.

The other thing is that I'm surprised of is that I seem to be the only one with this issue. Is this really that uncommon? Has anyone else had this issue?
 
Not only on the same angle but preferably also on the same plane. Anytime a u-joint shaft runs with unequal angles there will be differences in the rotational speed of the ends, the greater the angle the greater the speed difference, even with two matching angles the end RPM will be the same, but the shaft section between the u-joints will alter its effective rotation speed twice (IIRC) in each revolution, so if for example you were to replace a thin wall shaft with a thick wall item you may introduce/feel a vibration that was not apparent previously. The stiffer/stronger you make any attachments- solid bushes, mounts, low profile tires etc the more apparent the vibrations etc will become.

Jac would remove the driveshaft, stick a spare front yoke up the trans ext housing and find a mate to tow the car up to 80+ mph.... should be no vibration under that mode!
 
Last edited:
Top