Shims

[Suburban 90]

I am installing a 4" lift on my Suburban. I used my stock springs and the ORD shackle flip. I am wondering about drive line vibration while driving. While I have it apart do I need to shims the rear for pinion angle? I was hoping not to take it apart agian.

 

[y5mgisi]

On a burb you might be ok.

 

[Mastiff]

Someone else will chime in who actually knows, but from what I've seen, it looks like the shackle flips tend to rotate the pinion up a fair bit. This could be a good thing if you are going with a CV shaft, otherwise it would likely vibrate. I don't know how you can get it right in one shot unless ORD knows or someone on here has done your exact thing before (which is not unlikely at all).

 

[Suburban 90]

It does not vibrate with the 35's.

 

[paratrooper307]

It's always a trial and error thing, as even the same model trucks with the same amount of lift can vary from vehicle to vehicle. Other factors like tires, springs, axle swaps, extra weight, etc, can play a factor. A shackle flip is more likely to cause issues on a Suburban, as longer shafts don't need as much pinion correction for a given amount of lift as a shorter driveshaft.

Best thing to do is get a cheap pinion angle gauge (Harbor Freight has them for a few bucks) and check your angles to make sure the u-joints are in phase (conventional shaft) or that the pinion angle is pointing at the transfer case and is down a couple degrees of the driveshaft angle to account for axle wrap (CV shaft).

You can use a shim to rotate a pinion up or down depending on which way you install it. Of course the correct method is to cut and re-weld the spring perches, but I use shims and they work just fine.