Interesting and very informational link I found on researching pinion angles. Figured I'd share.

http://www.vibratesoftware.com/html_...es.htm#Measure

Seems that GM trucks typically have trans, shaft, and rear upward angles. Most sites I've found say rear should be a negative (down angle).

I have a vibration after my drop only during mid to hard acceleration. I need to double check everything but so far I've measured a 6 degree up angle on the trans, a 1 degree down driveshaft angle, and a 5 degree up angle on the rear pinion. Basically a 1 degree difference in working angle which should be acceptable for static, and makes sense since I don't have a vibration except under acceleration. The rear end is wrapping up and will probably never know how much. I plan on shimming 2 degrees, pinion angle up and trying it. Might have to go 4 for the torque.

 

I think you will be fine making your pinion angle set at 4* up. It shouldn't flex anymore than that.
Use a 1* shim and that should do it.

Jim

 

That's a great site, I've linked to it at least 4-5 times here when referencing pinion angle issues, which I had to get intimately familiar with when I broke my driveshaft.

For a 1-piece driveshaft it's a rather simple matter - transmission output shaft and pinion angles should be equal and opposite. It's when you get to 2-piece driveshafts that it gets more complicated (although as a rule there are fewer issues with a 2-piece).

 

After lots more reading and thought this is really easy in theory but complicated in application. I think its very important to get right. It would be easy to throw a shim in and call it good if vibration is gone but the u-joint working angles and unacceptable component angles could spell failure.

Here is a simple spreadsheet pic I've thrown together to aid me with it. Questions to myself etc.... Comments welcome.

 

Well here is what I've come up with after a lot of study and measuring with my $10 Lowes angle finder.

Present angles. Static
Front/Transmission
6.5* Up
Drive Shaft Angle 1* Up
Working Angle 5.5*

Rear/Pinion
5.5* Up
Drive shaft angle 1* Up
Working Angle 4.5*

Working Angles >4* BAD
Working angle difference front to rear >.5* BAD
UP, UP, UP configuration - Acceptable

The easiest fix to this that I've found so far is to shim the rear of the tranny. I'm using AutoCad to simulate different angles and moving them around and a 68" driveshaft. I've ordered 2 1/8 tranny shims from GM and am going to shim the tranny up 1/8". The concern with this is that it will now possibly screw up the front shaft angles but if it does it's literally a 10 minute job to undo.

Calculated Angles after shimming the tranny.

Front/Transmission
5.5* Up
Drive shaft angle 1* Up
Front working angle 4.5*

Rear.
5.5* Up
Drive shaft angle 1* Up
Rear working angle 4.5*

Working Angles >4* Better
Working angle difference front to rear 0- Acceptable
UP, UP, UP configuration - Acceptable

Anybody with any experience with this please chime in.

 

Your "supposed" to have working angles in the u-joints of less than 3* and more than 1*.
The diff should be 1/2* to 1* lower than the tranny due to wrap up.
Do you think this is acheivable?
It seems as though the pinion angle is where it needs to be in relation to the tranny. Since placing a tranny shim in is pretty easy, you should start with the smallest shim and see how it works out for you. If the vibration stops, then you got it right. Your angles may not be exactly what they need to be, but on most 1-piece DS applications I don't see why not.
Are you sure the pinion angles and tranny angles are 100% accurate? The diff angle is usually the hardest one to measure.

Jim

 

My problem was different, I didn't lower mine. I was just working with a vibration after the 4.10 install. So I don't have the same beginning cause as you, but, any vibration in the rear drivetrain can wreck havic on the pinion bearing. My vibration wore out the pinion bearing and the ring gear took the brunt of it all. So after you get your working angles, pinion angles, and tranny angles all happy...no matter if the problem goes away or not, I'd pull of your rear end cover off and examine those gears. And while you are playing with the angles, check the pinion bearing for play.

Just hate to see you put all of this work into getting it right and the vibration never goes away. BUT you actually fixed it, just there is another issue that snuck up on you...a bad pinion bearing. Not that it's your problem, but first sign a bad gear or pinion bearing is haunting you is vibration on acceleration.

 

this is way over my head. jim do you think you could check my angles? i get a vibe on the freeway just cruising. i just ignore it lol. its not a bad vibe at all

 

To get everything "tightened up" to perfect is achievable but not with off the shelf parts. I'd need custom shims. I want to get close and see if it affects the vibration, if it goes away I WILL get it perfect.

I am confident in my angles. Measured several times at different points and they repeated.

 

I may be in denial and if I hadn't done the rear end myself I would believe its the rear end. The vibration started after the rear gear/diff install and before the suspension drop. I am rationalizing that the bigger gear torque is putting more axle wrap into the equation. New ring, pinion, diff, bearings (Timken), perfect backlash, mesh pattern. Since your PM I have checked the pinion for play. None that I can feel and rotates smooth. The rear has less than 500 miles on it. It's near due for its breakin oil change so I will be in it. I'll recheck pattern and backlash then and look for something obvious but don't have a clue how to check the bearings without tearing it all apart again and then it would have to be visually burnt or something.

I bought a set of spring clamps last night and am going to put them on to test axle wrap theory. Wondering should I clamp front or behind the axle? Thinking
front?