If your using an angle finder, here's an except from one of WOL's write up's


89. Place an angle finder on the flat base of your front axle as shown in this pic and determine what your caster angle is. From the factory, your caster angle is a +4.2°. For 3" of lift and 35"-37" tires, I would recommend that you set your caster angle at about +7°-8°. And, if you set your front upper and lower control arms to the specs I have provided, your caster angle should be about there now.


That said, mine's at 6* by way of angle finder.

 

I agree as if it's power train vibration the driveshaft would be a likely cause. As implied before, I thought the vibration was coming from the front tires and steering wheel, which would indicate increasing caster.

 

i just had an alignment taking the arms loose and changing the castor wont mess with the alignment will it. also if i take the front shaft off and drive it that should tell me if its the drives shaft or something else.

 

Changing castor is part of your alighnment. If you take the ds out and no more vibes, it's either your castor or the ds. Is it an aftermarket shaft? If you still get vibes with your frt ds out, it,s most likely the rear ds.

 

Your lift is similar to mine but my caster is 4* or less. I think you can find pics of this in my sig. I measured 6* of ds to pinion angle here and it sounds like you may have more which will induce ujoint wobble. You may have to back off some caster. 6* is pretty steep but I have no vibes.

 

my thoughts too

 

its stock ds. i dont think its the back because i didnt do it till i messed with those arms to increase castor im gonna back off and see what happens. let you know after.

 

If caster and drive shaft angle are correct from stock, and you mod it, then once caster is back in spec, drive shaft angle will also be in spec. Since the two cannot be adjusted independently, this would be my goal. I wouldn't try to "add" more caster than necessary, because then the drive shaft angle will be incorrect. Before any mods, you really should get a baseline alignment, so you'll know how much caster you have initially, and where to put it back when all the mods are done. Caster does not care how big your tires are. It's effect on steering will remain unchanged. I think this is where most people open up this can of worms. They try to dial in way too much caster and end up with driveline vibrations.

 

I have fought with a slight vibe at 55-60 mph. Lessened with decreased castor. Currently at 5 degrees. With the 5.13 gears I just had installed, that same vibe is now at 45 mph. Makes sense since the DS is spinning faster at a lower speed with the new gear ratio. I took 3 full turns out of the front lowers to drop the castor from 7 down to 5 degrees. Vibe is almost totally gone. I'm going to try one more turn, but It may make the front too shopping cart wheelish. It was nicer at 7, but don't wan't to create problems down the line.

I finally gave in and had my tires balanced with rim weights on both sides. I was present when Jeff at Adrenaline Offroad (Burtonsville, MD) ran my previous inner rim balance on his machine. They were all way off. Now run totally smoother!

PS. Don't get Redneck Jeep started on castor, you'll get more than you bargained for! Just kidding ofcourse!

 

i backed off the arms a little brought it down to about 4.5 -5 and it seem to have cleared up the vibrations. thanks for the help.