I'm working on a Ford Fairlane with a hella of a viberation. The 9" was overhauled using all new American parts by a good Ford line machanic working for 30 yrs. I have the unit on jack stands with the drive shaft removed, started car and ran the 4 speed through the gears. No viberations. Now the driveshaft was balanced and new U joints installed both ends. The only thing left that I can think of is the rear end. If you're thinking pinion angles, that could be it but how do you change angles. I've installed new springs and hardware [rubber bushings on top of springs] and am at wits with this Gal. Any thought about my problem?