On shakedown runs, car pulls strong through the gears. Pulls straight and I feel no real vibration. When I back off of the throttle I get what feels like a driveline vibration from the rearend moving forward. I am running ladder bars, 9" and spool. Tire balance and driveline runout are good. All new parts as car was just finished. Checked pinion angle it is 1 degree down at ride height. Checking tech archives I see most people are running 2 to 4 degrees down. Could this cause my problem. No change when braking.

Why would the rear be moving forward.... shouldnt...
if it is a pinion angle issue it would most likely
get worse on the decell if you put more pinion angle
to it... JMO

Ring/pinion setup issue..? Sounds like too much backlash maybe coasting.

Sorry Mike I worded that wrong, Feels like it starts at the rearend just can feel it transfer up the driveshaft. Everything in the car is solid mounted so that may intesify it. Everything under the car is tight. Galen

Thanks Fred, it does have a lot of backlash. I questioned this and was told he sets Pro gears up a little loose.

u-joint?

Try running it on jackstands under the rear end housing and see if it does it at the same RPM and so on. Let us know what you find

jack stands won't be the same as on track,when you lift the rearend will rotate down under load changing pinion angle.my 63 belvedere vibrates a little after 100 mph but after 115 its a lot worse,only a 11.90 car.