The driveline is loosely balanced at the factory (they choose complimentary components to try and have minimal imbalance). However, they dont do more than they need to. They only balance things enough to accomodate factory gearing, which is why gears often require an alum DS. Some shops balance the DS while it's on the car (so they can balance it in its true dynamic).
It gets pretty complicated (to a simpleton like me anyhow) with the primary and secondary resonances in the driveshaft.
Anyhow, $35 is a great deal on a balance. Nice going!
i once had a vibration towards the back...well it turned out two of the rear d/s bolts(the ones that connect the d/s the the rearend) had loosened and it varied with speed...just another thing to check..make sure everything is torqued..
i once had a vibration towards the back...well it turned out two of the rear d/s bolts(the ones that connect the d/s the the rearend) had loosened and it varied with speed...just another thing to check..make sure everything is torqued..