Will I need shims with 1" over shackle lift?

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Jun 24, 2005
Omaha, Nebraska
Im installing all new urethane shackle bushings. While I have everything apart I want to install new shackles too. They will be homemade, using the ConFerrs on my 40 for a pattern. They will be approx. 2" longer than stock, so roughly 1" of lift.

Id like to have everything I need gathered for the job since the truck is my DD. 1) Do you think I'll need degree shims for that much lift? 2) If I do shim, will I need longer center pins? 3) Should I replace U-bolts if I do shims?

Thanks, Hodag
My guess is that you don't need them. The ideal way to check though would be to go get the caster angle measured at an alignment shop when you are done. If it's in spec, you are good to go. If you are out of spec, they can tell you what degree shim to add to move back to spec. There is also the "seat of the pants" test - ie drive it and evaluate.

If you remove u-bolts, you are supposed the chuck them, and only install new ones.

On the center pin question, it's the length of the head that's important. (No comments please...I have a fragile ego!!!) You can lengthen the head by using washers, or a nut under it. I've used a nut, threaded onto the shaft (no, it didn't hurt, for long...) I just ground the nut on a grinder to be the same shape as the head. Voila, long head.

Note on center pins - they get pretty rusted. Be prepared to replace them.
The mos importan measurement to know that is the caster .. .84 min and 2.34 max ..

But I'm pretty sure with 1" long shackles you don't need em ..
I've been running the Specter 1" extreme shackles for a couple of years now without shims, and without any issues. The truck tracks straight down the highway with no wandering.
With a lot of help from 2badfjs I added 1" over shackles, bushings and different springs last weekend and didn't use any shims. It's fine, no vibration, no wander at all.
thanks guys. Youve confirmed what I expected.


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