Vibration after rear end install?

[OneStiffGT]

I just put in a 9" rear end on my car.

I also got the steeda adjustable upper control arms.

There is a slight problem, there is a vibration coming from the back of the car after around 30-40 km/h.

It still does it in neutral, or even when I let go of the gas, not just when I am accelerating or decelerating.

I've got a Moser M9 with a full spool in it.

Tire pressures are equal on both sides as well.

What could be the problem? Is it because the pinnion angle isn't right?

Should I even drive the car to get to the shop to get the pinnion angle set, or should I trailer it?

 

[BobHyatt]

maybe

Is the pinion angle correct? If you install a new RE, and the nose is pitched up or down just a bit, the universal joints will start to rumble because beyond a certain angle (pinion angle) the joints have to speed up / slow down as they revolve, setting up a potential vibration.

You could put it up on jack stands and have someone outside the car as you slowly increase the speed and see if the source of the vibration can be seen. Go easy as you can get some backlash from the unloaded wheels, thru the clutch anti-chatter springs. On hi-po clutches, they don't like that kind of chattering.

You could just have a bad/damaged U-joint too. The driveshaft flange might not be tightened. Or it might have some trash/grit/etc under it preventing it from seating fully, which would cause wobbling and the vibration you are feeling.

And, of course, it is possible that you have a bent axle or any of several other damaged parts (bent pinion shaft, etc) that will cause this.

 

[OneStiffGT]

I haven't measured the pinnion angle, but the diff is definetly pitch down.

The car is an automatic, so no clutch.

The U joint is brand new, but it might be defective... Also the flanges are all tight, with thread lock on them.

I'll try to set the pinnion angle and see if the vibration goes away.

Everything in the rear end is brand new, so I doubt that the axles or etc. are bent