Originally Posted by RBob

Fixing vibration problems can be difficult. What I do is to place the
rear on jackstands with the tires a few inches off the ground. Then
raise the front a few inches to match. This is so the vehicle is level.
Note that the rear jackstands are under the rear axle assembly, out by
the trailing arms under the spring seat.

Now start the engine, place the trans in drive (or gear for a stick),
and gently run the MPH up to the point of vibration. Note how it feels,
and remember it. If there isn't any vibration, let the car down and
check the front tires, struts, and such. It isn't in the drive train.
Also check the engine tune, a misfire will cause vibration issues.
Sometimes this can be diagnosed by noting if the vibration occurs only
when the TCC is locked.

If it still vibrates on the jackstands, remove the wheels/tires and
place the lug nuts back onto the axles. Torque lightly. Still vibrated

Start the engine, place the trans in drive (or gear for a stick), and
gently run the MPH up to the point of vibration. Still vibrated


If it doesn't vibrate anymore there is an issue with a/the wheel/tire
assembly.

If it vibrates, remove the brakes drums or rear rotors (which ever it
has).

(AT THIS POINT DO NOT DEPRESS THE BRAKE PEDAL).

Start the engine, place the trans in drive (or gear for a stick), and
gently run the MPH up to the point of vibration. Still vibrated

If it doesn't vibrate anymore there is an issue with a/the brake
drum/rotor assembly.

Before I opened the rear, I put a yoke in the back of the tranny and ran it up to the vibration point. NO VIBRATION!

If it vibrates, pull the axles out. Note that 9-bolt and the 7.5/7.625"
rears are different in how this is done.

Start the engine, place the trans in drive (or gear for a stick), and
gently run the MPH up to the point of vibration. Still vibrated

And so on. . .

The next would be the carrier, Still vibrated then the driveshaft NO VIBRATION(need a yoke in the
trans tailhousing for this). If it smooths out with the driveshaft
removed, the issue can be one or more of three items. The driveshaft,
yoke, or pinion gear. I swapped back to the steel shaft and had the vibration at the same point.... I feel pretty safe to say it isn't the driveshaft.

Originally Posted by Andy30thZ

I have tried just changing the pinion bearings, but the vibration is still there when I run it on stands with just the pinion..HUH? Pinion yoke problems?
This is a "spare" rear I picked up with broken 4.10's. I installed 4.10's out of an 95 S10 and have no whine, no problems, except this vibration. I can't see any damage to the pinion housing, could that have been a problem?
Thanks!! Andy

Originally Posted by chief455

thankfully you did a nice job isolating the cause to the rearend.
Rather than ponder and theorize what could be wrong I'd pull the rear apart, inspect, replace and reassemble.
Eliminate the variables - could be side pinion gears, gear, axles - anything really. I'd rebuildthe rear and let us know what you find was damaged.
Good luck!

Originally Posted by Andy30thZ

That's what I did. I isolated the pinion by removing every part of the rear and checking for vibration on stands. Then I pulled the pinion and put in new bearings and races, reinstalled the driveshaft and ran it up to the vibration point with nothing in the housing but the pinion. It still vibrates. Everything "looks" OK.
If there is nothing turning but the motor, tranny, driveshaft, pinion and there is no vibration with the driveshaft removed....it has to be in the pinion or driveshaft, right? I had the driveshaft checked for straightness and balance and they said it is OK. The slip yoke on the LS1 shaft had a little play, so I swapped it for the yoke from my steel shaft. It still vibrates.
I'm not sure where to go from here?

Originally Posted by chief455

WOW! that's how I read it - but never heard of anyone try it - very good job

Originally Posted by Andy30thZ

Yeah, I spent $600 on new rubber that didn't fix the problem... That kind of pissed me off to waste money without really knowing what the problem is.
Now I'm confident I know where the problem is..... Just I don't know what to do about it.
When I install the pinion I use an impact wrench. Is it possible I'm screwing something up when I'm reinstalling the pinion?
Also, this rear has a pinion yoke with no weight welded onto it. Are some yokes zero balanced and others are balanced as a assembly? (with driveshaft?) HMMM?
This rear came with LCA relocation brackets. My car is stock height, stock contol arms. I am running the middle hole. Relocation brackets shouldn't change the pinion angle, just the torque arm, right? RIGHT
There must be some way to measure runout on the pinion yoke?
GOOD IDEA. wITHOUT THE D/S INSTALLED PUT A DIAL INDIUCATOR ON A ROUND SURFACE OF THE YOKE AND ROTATE IT IN CIRCLES BY HAND LOOKING FOR VARIATIONS ON THE INDICATOR DIAL. COULD BE JUST THE OUTER CASTING GETS THICKER IN SPOTS AND THE CENTERLINE STAYS - MAYBE TRY AND PUT THE INDICATOR ON THE ATTACHING NUT OF THE YOKE AND WATCH FOR RUNOUT AS THAT ROTATES .
There has to be a way to diagnose what is wrong with this thing before I spend more money!