Any Driveline/Pinion Angle Experts out there?

[hotrodz37]

Alright y’all, I have an issue with my truck rumbling while slowing down from 30-18mph. Completely stock 2019 2wd denali with the 8 speed. I’m thinking it’s pinion angle related. My truck has 2* shims from the factory with the fat end toward the front of the truck which in theory should point the diff down.

 

I measured everything today and the working angles from the rear end to driveshaft are way off. Pics attached. In theory I would need to add even fatter, maybe 4* shims to point tbr rear differential more towards the ground

which doesn’t seem right.

 

A few of the 2020’s I have driven (same truck config) didn’t have shims and didn’t have this rumble near as bad.

 

Measured with an angle finder app and also a magnetic digital angle gauge.

 

Here are the numbers (pics attached as well):

 

 

Trans - 5.45 down

 

Shaft - 5.2 down

 

Rear End - 1.56 down

 

 

 

 

 

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[Maven]

Swapping a 2deg shim with fat end forward, to a fat end rear orientation will result in a net 4deg up rotation of the pinion. Which if your trans is tail down, is what you want.

[hotrodz37]

Yep, wound up doing that this weekend and problem is completely gone. Amazing a backyard mechanic can figure it out but leaving it at the dealer for a week they had no idea what was causing it. 

[Maven]

Be easy on the dealer techs ..... Some of us are okay  

[hotrodz37]

2 minutes ago, Maven said:

Be easy on the dealer techs ..... Some of us are okay  

 

Haha don't doubt it! 

 

Question for you - I wound up rotating the shim, took care of the problem but after measuring the rear working angle is a little too much. The sweet spot would be with no shims.

 

1) Do you have any tips to get the centering pin all the way out? Mine got stuck half way through the leaf pack which is why I just rotated it instead of taking it out completely. 

 

And 2) Do I need to replace the u-bolts? I have heard they are a one-time use part (I've had them off twice now).

 

Appreciate your feedback! 

[Maven]

No tricks on the pin, though I'm not certain I understsnd why you wanna remove it.

 

According to the service manual, they are reusable. Tighten nut to 59lbft, back off half turn, tighten to 59 again, then another 130degrees.

 

While it's possible the manual is wrong, I believe the confusion comes from the fact that the K2 trucks had one time use fasteners in the springs.

[hotrodz37]

5 minutes ago, Maven said:

No tricks on the pin, though I'm not certain I understsnd why you wanna remove it.

 

According to the service manual, they are reusable. Tighten nut to 59lbft, back off half turn, tighten to 59 again, then another 130degrees.

 

While it's possible the manual is wrong, I believe the confusion comes from the fact that the K2 trucks had one time use fasteners in the springs.

 

Got it, thank you. Huge help!

 

Wanting to remove the center pin so I can remove the 2deg shim completely. Without the shim the angles will be exactly where they need to be. Not sure why they were included on my truck to begin with. 

Edited August 24, 2020 by hotrodz37

[lapoolboy]

1 hour ago, hotrodz37 said:

 

Got it, thank you. Huge help!

 

Wanting to remove the center pin so I can remove the 2deg shim completely. Without the shim the angles will be exactly where they need to be. Not sure why they were included on my truck to begin with. 

Are you putting two C-clamps on the leaves on either side of the pin before you try to take it out?  

[hotrodz37]

Are you putting two C-clamps on the leaves on either side of the pin before you try to take it out?  

 

Yeah, putting spring clamps on I had laying around. Probably pulling the springs just slightly out of whack so the springs aren’t perfectly aligned huh?

 

I’m guessing I should ease up on the tension of them I’m guessing until I get the pin out?

 

 

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[lapoolboy]

Put real C-clamps about an inch to either side of the pin and cinch them down tight.  You can drive the pin out with a small punch if you have to.  One of mine I had to "unscrew" out of the leaf pack.

[hotrodz37]

Put real C-clamps about an inch to either side of the pin and cinch them down tight.  You can drive the pin out with a small punch if you have to.  One of mine I had to "unscrew" out of the leaf pack.

Appreciate the tip! Yeah one of mine I had to unscrew and it got bound up halfway through the leaf pack. That’s when I decided to just spin them and try it to see if it even took care of the problem and it did, hallelujah.


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[kpanza]

Yeah, you need to use real c-clamps as lapoolboy said.  Get them tight as close as you can to the pin.