Hey Guys,

I have done a search and got a few ideas but I'm still not having any luck. I have a '70 with a zz502, 4L80E, and a 9 inch rear with 4:10 gears. At about 65mph theres a vibration which feels like driveline. I have replaced the trans mount with a shorter one and tryed changing the pinion angle. I have checked my angles with an angle finder and they appear to be right on. I took my new custom 3 " driveshaft back to have it rebalanced. Nothing seems to work. If I change the trans angle or the pinion angle in either direction the vibration gets worse. HELP!!

which feels like driveline

But is it ?? Have you had all of the wheels and tires balanced, or at least checked ? Does it do it in high gear only, or will it do it at the same speed in 3rd ?

Did the same company that made the shaft check it, or someone else ? Might want to have someone check it to make sure the u-joints are properly phased.

Check for rough Pinion bearings.

Thanks for the ideas Bill and Randy. The vibration does occur briefly at high RPMs like between the 2-3 shift at full throttle. The same shop did re-balance the shaft, but recently had their machine recalibrated. They are also top shelf and have built several shafts for me. The vibration feels "between the bucket seats" not at all like a tire/wheel out of balance. Dave