Help needed something not right with my new 9 inch diff ?

[ozkiwi]

I just had a brand new 9 inch diff fitted to my truck and it has a drive line vibration since it was fitted so I stuck it on the stands and put it in drive to take this video so someone who knows can tell me what is going on.
At first glance I thought the drive shaft was bent but as I followed the wobble back it is starting back at the pinion yoke or pinion itself.
I paid big money for this diff and before I go back to builder who is supposed to be the guru off diff's I want to know what I am talking about.

Have a look at the video and tell me what you think.

https://www.youtube.com/watch?v=UnhZ...ature=youtu.be

[wraprail]

I have a 9 inch in my C10 too but I have the shorter pinion yoke. What u-joint are you using? Is it a conversion joint or ?

[geezer#99]

Your pinion angle likely is wrong!
Your u-joint looks to be binding.
Check this.
http://www2.dana.com/pdf/J3311-1-DSSP.pdf

[nheller76]

Agreed pinion angle is off. Raise the tail housing of your trany some.

[ozkiwi]

Ok the angle is off but that does not explain why the drive shaft is going up and down and the pinion and yoke are causing that.You have to look close and the video is not that good but the pinion yoke looks like it's bore is off center or the pinion shaft is not straight (you can see it clearly in the last 10 seconds of the video).
Can anyone else see that? If you look at the last 10 seconds of the video

I am no expert but that does not seem right to me.

[smashingchuck]

Fix what is known first. An imaginary line drawn thru the output shaft and and imaginary line thru the pinion shaft should be parallel. In other words, at the same angle, not pointed at each other.

The camera shakes a lot in the footage which makes it really hard to get a good visual on the run-out situation you describe. try doing some run-outs with a dial indicator on your driveshaft and pinion shaft if youre thinking that's where the problem lies. I think you can get a dial indicator with a magnetic base at harbor freight.

[bdiamond]

It looks to me like the ujoint isn't sitting in the yoke right. I'd loosen the straps and see if theres a problem there...

[ozkiwi]

Lot's of thing's to check before I go back to the company that built the diff on wednesday.
The video for some reason does not show the extreme run out on the yoke and
drive shaft which is 1/4 inch at the Universal on the drive shaft and about an 8th at the yoke by the pinion seal cover.
I think now it is 3 issues the universal joint and the pinion yoke plus the alignment.
Thanks for the idea's and I feel better equipped to talk to the builder now rather than just saying the truck vibrates since the diff was fitted.
Will post the end result when it is sorted

[geezer#99]

You started off with an alignment (pinion angle) problem that created your run out (due to u-joint binding) which has likely ruined your u-joint, your yoke and possibly your pinion and pinion bearing.
Who installed the complete rearend?

[greg64]

To me, it looks like there is excessive run-out on the pinion yoke. In addition, there doesn't appear to be enough angle in the pinion u-joint; the driveshaft and pinion are too close in alignment. How was the pinion angle set? It's clear with the new 9 inch that the spring mounting pads must also be new. I'd try loosening off the u-bolts (hey at least they're not seized yet) and then shim the front side of the spring pad an 1/8 inch, so that the pinion rotates *down*. This should put a small amount of angle into the u- joint, plus the pinion will more closely align with the transmission output shaft, which is the goal.

Here's another tip; trying to measure the pinion angle and tranny output angle accurately is tough with an inclinometer. When I set up my 64's driveline, I jacked up the rear axle until the pinion angle read perfectly level. The axle had to be lifted about 18" but it's possible. Then I put the level on the transmission, and raised and lowered the tranny mount until it too read perfectly level. That's the height I made my custom crossmember at to support the tranny. Guess what? No vibration at all from the draft shaft on the maiden voyage. And now, 25,000 km later, it's still perfect.

[ozkiwi]

Originally Posted by bdiamond

It looks to me like the ujoint isn't sitting in the yoke right. I'd loosen the straps and see if theres a problem there...

Yes that's exactly what the problem was(well spotted) and it had been like that for a long time.The universals had some sort of pin location system I had never seen before and was pinned a 1/8 of an inch off center.
I fitted a brand new drive shaft with ford spec universals both ends as the old shaft was pretty rusted and thin when they cut it to change to ford style yokes.

No drive line vibration for the first time since I have owned the truck.
Very smooth now.