Rear End Noise and Clunk

[jmanscharger]

When my (automatic) car shifts gears the rear end makes a little noise and jumpy vibration. It is a 70 RT that was previously converted to automatic. Local mopar pres checked the pinion snubber and did not know what was causing the jump either. It is not terrible, but when I put it on the lift might it be a simple as a u joint? What do I look for first?

[Just 6T9 CHGR]

Could be excessive backlash in the gearset.   Make sure the pinion nut is tight as well

[Ghoste]

Check for slop in the u-joints.  Simple as moving them by hand.  They should be tight and not have any play in them.

[firefighter3931]

Both of the above suggestions are excellent. Something else worth looking at is the rear trans mount on the crossmember. A seperated/weak mount can cause vibration when the tranny upshifts.

Ron

[Chryco Psycho]

do you have the stock pinion snubber or the aftermarket race one , it will hit the floor when shifted into gear sometimes

[Ghoste]

I'll add that a bad trans mount can also be the cause of some of the vibration questions that come up all the time.  I've had them cause both constant and pulsing vibration and contribute to a death rattle.
Pinion snubbers can also be a cause of "suspension" noise just ddriving around.   Using them with weak or some stock leaf springs will allow them to thump the floorpan just going over road irregularities-sometimes loudly but sometimes just loud enough for you to hear and wonder what you broke now.
Neither of those points have anything more to contribute to your question but for anyone else following this thread, I thought I'd mention them to keep in mind on other related noise and clunks.

[Steve P.]

4-speed cars tend to beeat the snot out of rear ends..