I put a 4" lift on my burb(which actually gave me 5.5" of lift) the other weekend, but now I notice that I have a vibration in the front shaft. I know I need to shim it, but how do I figure out what degree of shim I need. I did a search and found this weird thing: </font><blockquote><font class="small">In reply to:</font><hr /> Remember High School geometry? This is what it was for. Measure the distance between the spring eyes. Stock shackles are 4". Using the front spring eye bolt as the center of an imaginary circle, the rear spring eye has traveled in an arc a little more than 2". The circumference of the cirle is 2*Pi*(distance between eyes). Divide the arc length by the circumference and multiply by 360. This is how many degrees you have moved your pinion. [/ QUOTE ] Does this equation really work? Can someone explain how it works and how to come up with some of the numbers so I can get the right shim? Or is there an easier way of figuring out the shim angle?