@white08gt - It had the 2.5 degree shims in it and I didn't have any drive line vibrations after everything was installed. I also have an regular diff with 3.31 gears. I returned everything back to stock last night and still have the vibration, so the shackles and shims weren't the issue.. Only time will tell what is.
Can anyone tell me if adding the FX2 wheels with stock 275/55R20 tires in place of the stock 255/60R18 wheels and tires would alter the truck's pinion angle? I'm trying to be told that the OEM wheels/tires are the reason for my drive line vibration.. I understand that slighter taller tires will throw off an odometer slightly, but that's about it. I thought you'd have to alter the suspension or angle of how the engine/transmission sit in the truck to throw off the pinion angle.
It is not the 20" wheels and tires. It looks like we have done the exact same mods. Mine is a 2013 5.0L RCSB STX. I did the Rough Country shackles first with no shims. I heard talk of a slight vibration around 20mph when taking off from a stop. I then started to notice mine had that vibration so I bought 2 degree shims and installed them. The vibration was still there. All of this is before I bought my FX 20" wheels with Bridgestone tires. So, I can tell you for a fact it is not the larger wheels which makes no since since they are intalled on other models.
They're keeping my truck over the weekend and are going to install the factory wheels/tires that it originally came with to see if it is in fact my FX2/FX4 20" wheels. I'll let you know what they come up with. If in some way, shape or form does come to the 20" wheels/tires, I want to know what they did with the 2014 Tremor to make it work over my truck. From what I can tell, the Tremor has different rear-end gear and an EcoBoost engine.. Besides that, it would still ride on the same wheels/tires and have the same drive shaft length/setup.
They are just screwing with you. Wheels and tires have no impact on pinion angle. Ask them to measure pinion angle before and after to prove your point. Hell, I'd ask for a different tech if I was told that.
__________________ 2012 F150 EcoScrew 4x4 XLT 157"wb MaxTow LEGAL DISCLAIMER: Anything I or anyone else says about my vehicle on this website or any other website, pertaining to modifications, is only to gain acceptance from my/our peers, and does not actually represent anything actually existing on my vehicle, and thus, cannot be held against me in any issues, i.e. warranty claims, that may arise.
I got my truck back today. They road force balanced my pirellis. My vibration is gone. I don't know about the pinion angle being off, because my truck isn't doing it anymore. Not like it was before I brought it in. Before I brought it in, my steering was also off to the left. My alignment was fine, but the wheel was off.. After they balanced my tires, it's now centered. I really think I have a bad batch of Pirellis. I've heard how many people hate them and can't believe they come from the factory. Going to probably get rid of them and get some Bridgestone H/L Alenzas. I told my dealership I feel like I'm taking crazy pills, but all my issues are resolved.
There is NO way in hell that tires being out of balance can cause the shudder in that window from about 17mph to 20mph and be smooth at all other speeds especially higher speeds. They probably greased that slip yoke on the drive shaft that others have talked about. Mine had the shudder whether I had stock 18" or the oem FX 20" wheels.
@LTNBOLT - I thought the same thing, but my truck no longer has the vibration. After they road force balanced them, the problem was solved. I wasn't charge anything done to my truck. I blame it all on the horrible Pirelli Scorpion ATR tires. They are the worst tires I've ever driven on. Going to start saving for Michelin LTX M/S 2 tires.