Mud in my Veins
Join Date: Dec 2000
Location: Memphis, TN
Thanked 0 Times in 0 Posts
Re: ar Vibration
Most people call the double cardan a CV joint, but it has nothing to do with constant velocity. The only reason for the DC is to split the total flex angle between 2 u-joints so there's no binding for high driveshaft angles. It does NOTHING to remedy the changes in rotational velocity inherent to the basic u-joint design.
Look at the front end of the rear d'shaft where it connects to the t-case. If you see a big cast collar with 2 u-joints about 3" apart, that's the DC. Inside, you can barely see the centering ball that keeps the shaft aligned. The u-joints & the ball may have needle-style grease fittings, but you have to disconnect the DC from the t-case to lube the ball.
If dropping the rear shaft cures the vibe, then it's definitely the shaft balance, yoke nuts, u-joints, or DC ball causing it. If the vibration stays, it may still be a rear axle problem like u-bolts, R&P, or wheel bearings. Also, bear in mind that the front axle may have vibrations of its own, so be careful to ID the source if you still feel some vibrations when driving in FWD.