After adding the 4* shims it seems like the alignment is slightly off? Is that a possibility just by adding shims to the rear end?
I'll be haviing it checked but am just curious.

 

Maybe the rear axle isn't square in the truck anymore. Take some measurements and see. If it's off just a little the alignment may not pick it up. the'll just screw up the front to match the screwed up rear. then you'll be crabbin down the road. so take some measurements and see.

 

I dont think the shims will affect the alignment. You are just changing the angle, not the height.

 

It could throw off the cross camber and cross caster adjustment.
That is the squareness of the front tires with the rear tires.
Theoretically, the shim installment should not affect the alignment if everything went back together "exactly" like it was prior to the shims installment.
Unfortunately, that doesn't always happen. Go back over your work and have your alignment checked out.
In my opinion, any suspension change (front or rear), it's recommended to have the alignment checked and or reset.
As mentioned above, the riding side-saddle or crabbing down the road scenerio, usually happens when a suspension component is install wrong, is not leveled and trued, or a vehicle was not repaired properly from a severe rearend or frontal collision.

Jim

 

I am re-aligning it on thursday. Hopefully all is well.

 

Just curious, but who is running 6* shims with their lowering kit?
I've heard of guys using up to 4* shims, but not quite 6* ones.
How low is your drop??
What all was done to lower your truck anyways?

Jim

 

I have 4 degree shims with a 4" drop.

 

It is quite possible that installing the shims threw your thrust angle off (Thrust angle is the angle of the rear axle, which will actually decide which direction the truck will go). You want your thrust angle as close to 0* as possible. Anything positive means that the rear axle is pointing to the right, making the truck want to track left, and negative is just the opposite. Which direction is your steering wheel pointing when going down a flat road? If it's pointing to the right, that means that the truck is dog-tracking left and you have to compensate by turning the wheel to the right, and vise versa.

If one shim is in further than the other, that could change the way the rear diff and axle assembly is aligned. Might have to loosen up the rear U bolts and moving the shims around a bit.

 

The drop is about 4" in the rear. The shims are 4*. And yes, it's pulling right a hair and i'm having to compensate left.
I am taking it back to the alignment+ shop and have them square it up again on thursday. Right now the truck is getting the hood blended in (color) better and tweaked.
I would hope the alignment shop would have no problem correcting it?

 

Explain pulling to the right a hair?
A hair is a drift. Very common with the GM trucks. More than likely, if it's a slight pull or drift like you describe, an alignment correction to the Caster adjustment will fix you right up. A -1.0 to -1.4 Caster split works best on the GM trucks. They tend to like to track to the right from the factory.
I have a -1.2 caster split and I still have a slight drift to the right. I will have them bump it to a -1.5 next time.
Just let me know what your alignment specs are when you get the alignment done. A good alignment shop will give you the print out of the alignment specs.
Hope you get it all straightened out.

Jim