With the double cardon joint up by the transfer case you need to run almost 0 diference between the drive shaft and pinion yolk especially with the low gears. My caster was at 2.5 to almost eliminate the 45 to 50 vibs I had. I am at 4.10's now so it was not as noticable as with the 5.13's that I had originally. Just turned my C's to 6.5 degrees to get it acceptable for my wife to drive. The lower the caster the more important it is to have everything in your front end tight and alinged correctly. You get more feedback through the wheel especially on off camber bumps or for example on the streets where a storm drain is located and they drop it off into the street so only the passenger side hits it. As long as you let the steering float or let it do its thing and not saw at it things don't get out of hand but my wife expects a car like feel you will never get out of a solid axle vehicle. With turning the c's it is all but gone. Big tires and solid axle you will never eliminate it. Here is a good decription of what someone else did to get his arm lengths correct.
"Try using Poly's front control arm settings, which are upper 18 3/4" and lower 23 1/4". To achieve the upper setting you'll have to use the inner holes on the upper control arm forks. Be careful that the end of the left front upper fork will not crush the locker switch on droop. I ended up just cutting the ends of the forks off and grinding them smooth. I was just at EJS and noticed most guys running this suspension had shortened the arms up and had done something similar wrt the upper arm forks. Using the shorter settings also prevents a lot of the problems with TF springs hitting the frame, sway bar end, track bar bracket, etc."
After getting everything how I liked I still took off the front drive shaft because there was just a slight drone at 50 to 60 mph. Just enough to feel but not a vibration. I haven't put different arms on the rear yet and am at 1.5 degrees difference in the rear and that is where it is coming from. This jeep had a ton of problems not including the thing being totaled from an engine fire so I have been working through them one by one. Harmonics from vibrations are a big problem since they can lead to premature wear and or total failure of components. Tires out of balance to the drive shaft vibe front to front and rear, ring and pinion problems, ball joint, heim joint and a ton of other stuff all can add up to nasty vibrations and or death wobble. Any of these problems or even slight wear depending on the vibration frequency in Hertz can add up to a worse vibrtaion and or a harmoinc of the added vibrations. Below expains it better than I!
"This law (Keely's 4th Law of Harmony) states that everything (any body of whatever composition or size) vibrates at a frequency relative to that of its innermost constituent part, the atomole. The frequency of the atomole representing the fundamental or keynote of the chord (the eigenfrequency of the aggregate). The chord's aggregated rate of vibration is in direct proportion to that of this same atomole. In other words, if the atomole resonates at C12, then the outer body or "coherent aggregate" will vibrate to a note somewhat lower in frequency, say C2, or any other note forming harmonic relations to that fundamental frequency (see any good book on music theory). Usually referred to as summation or difference tones (beat frequencies), these derived frequencies form the "chord of mass" of any aggregated mass or object.
A prime example is a piano wire which sounds a primary note, the one usually associated with it, yet at the same time, it resonates many partials above and below its fundamental tone (see James Jeans' Science & Music). These partials are related to the fundamental or keynote by definite mathematical ratios, the same ratios that are evident throughout music theory.
As further analogy, a football team, representing a coherent aggregate, resonates to the overall fundamental idea of winning. The team's ideal, then, is the fundamental or keynote. The individual players' ideal is also to win, but must remain subservient to that of the team. In other words, he must follow through with the motions of a given play holding in abeyance his own personal determinations. Whatever he does on the field, must reflect actions harmonious to that of the team as it goes through its coordinated moves. Dis-coordination means failure here.
As no thing can exist of and by itself (it has to come from somewhere), its mere fact of existence tells us it is composed of or derived from something else. Something else being either more or less than whatever it is. Or simply, an object is composed of two or more "substances" or it is derived from something "larger" than itself. Since we all know by now that everything is vibratory in its inner nature, then these sources from which a substance comes is also vibratory. Hence, combining or merging vibrations will create summation or difference tones, therefore, we can safely say, that all aggregated bodies are "chords of vibrations" derived from other "chords of vibrations!" And the rules that define these modes of combination are the same as those found in music theory!"
Now I am just being overly dumb but the gist is your jeep and anything else in life needs to be in some kind of Harmony or you will have problems! I guess look at your Jeep as your favorite football team and put a winning combination together that all get along nicely and you should technicaly have a great Jeep!
Good Luck!
