Let's play the WTH is broken game..

So I'm fighting a massive vibration problem in my daily driver s10.

2wd truck with manual 5 speed 4.3 v6
Heavy vibration at speeds higher than 55mph accelerating, and at any speed while decelerating
Pushing clutch has no affect
Braking has no affect
Replaced u-joints and carrier bearing
Trans mount is good
When running it up on jackstands and going though the gears vibration is still felt so it eliminates any front end problems or out of round tires.

Talked with Stickney briefly about it a few days ago and he said pinion angle
Because of course I can't leave stuff alone...and it's lowered 4" in the rear,
I did all kinds of shimming and not sure if it's worse or better.
On top of this (and to the point of the post) I noticed when the rear of the truck was up in the air on stands and the truck is put into gear I am able to spin both back tires by hand. They make the driveshaft teeter back and forth a little but it doesn't rotate. Am I missing something here??? Shouldn't I not be able to move the wheels while in gear???
It's a non posi rear, with the truck in N the wheels rotate the driveshaft and wheels turn opposite like they are supposed to in a limited slip.

Is something broken in the rear diff?

And any ideas on where the hell the vibration is coming from?

Just realized this should've probably been posted in the other GM section, so mods move if necessary

I was thinking driveshaft related. Out of balance or what Steve said. Trans mount/bushing and everything good?

Pinion angle is even 4* down at carrier bearing and 4* up at the diff.

Trans and everything before carrier is good. Running the truck with no driveshaft proves no issues with first half of driveshaft or transmission.

I'm thinking rear end related since I can wiggle the diff yoke up and down. I think the kid that owner it before me beat the shit out of it and smashed something in the rear.

I got a replacement today at Sam's so we will find out what's in there in a day or so.

Wow. Definitely not supposed to be able to wiggle that. Keep us informed after the swap.

Ironfistdog wrote:

Pinion angle is even 4* down at carrier bearing and 4* up at the diff.

Just remember, when youre driving the rear will torque UP so with rubber suspension components you'd probably be better with ZERO at the diff.
That way when you load the rear, you'll get the 4 degrees UP & angles will play nice together.
Pretty sure thats what we discussed the other night? No?

Ironfistdog wrote:

I'm thinking rear end related since I can wiggle the diff yoke up and down.

There's a clue....

Good luck

Yeah that is what we discussed and I understand it totally.

What I meant was that the pinion isn't out some crazy number. It's pretty close to being dialed in.


Took the diff cover off the donor rearend and I find 410 gears

Must've grabbed one from a 2.2l. Factory final gears in my truck according to the rpo is 2.73

Is this gonna make the truck undrivable if I use the 4.10's??

My route to work is mass pike/290/495....