Drivetrain Vibration

When accelerating in 2nd gear, or decelerating in any gear, I get a heavy vibration from somewhere in the drive train in my Model A. The engine is a 350 from an '80's Chevy pickup, and the trans is supposed to be a 350 out of the same truck. It's all stock - far as I know. Rear end is Camaro of the same general vintage, coil springs and all. The rear of the trans is in line with the rear end laterally, and almost in line vertically. Looks to me like the differential yoke points slightly under the trans. Haven't measured it, but looks like the driveshaft is about 2½ ft long. I've had the driveshaft out, the u-joints seem tight, and I lubed them. What do y'all think ??

Lar.

I think you need to put an angle finder on the trans output shaft and the diff yoke to find out if they are parallel. You also need to determine if the centerline of the motor/trans is parallel with the centerline of the car. You can move the motor/trans a little to the passenger side to make clearance for steering for instance, but the crank centerline must be parallel with the centerline of the car. If the angle of the front u-joint does not match the angle of the rear u-joint in both planes, you'll have problems. Look at the front as having a positive angle and the rear as having a negative angle. They must be opposite but equal and cancel each other out.

If its only when accelerating or decelerating, I'd look for the rear end winding up, slack in the locating arms.

Is the drive shaft balanced properly?

Haven't had a chance yet to really get under there, but driving it today, it seemed to have a strong harmonic coming in at around 35 mph, and tapering to mild at around 45 mph and up. I have no way to know if the driveshaft has been balanced, but going by the sloppy workmanship throughout the car, I'd say probably not. Rear end and locating arms all seem tight.