driveshaft vibration

[Beeper]

1075918

Could someone please explain the screw clamp method of balancing a driveshaft? Do you start by placing the clamps near the end of the shaft, middle or somewhere in between? I had a "moaning" vibration when my speed approached 50-55 mph. The vibration decreased at higher speeds. I rotated the driveshaft (after eliminating other causes of vibration ie. tires, loose bolts) 180 degrees and the vibration changed in frequency. The vibration is not as bad now, but does not go away at higher speeds. I want to try the screw clamps before taking the driveshaft out to be rebalanced. How successful have any of you been in balancing a driveshaft with screw clamps?[addsig]

 

[MudderChuck]

1076024

Sometimes the needle bearings in the U-joints for the driveshaft, dry out. A little play from worn U-joints and a little water displaces the grease. A worn rear bearing sleeve in the transfer case, will mess with balance. As will a lift and increased driveshaft angle.
The only time I suspect the driveshaft itself, is when a wieght has fallen off or it is severly rusted.
You didn´t say year or mileage, if your ride has about 100,000 miles and you have the 35C rear end, it´s time to take a pry bar and wiggle the carrier up and down and see how much play you have in the carrier bearings. Wheel bearings are also suspect, but usually start leaking or seeping into the rear brake drum.
Sounds kinda silly, but the test for an out of balance driveshaft (other than removeal and putting it on the balance machine). Is to change the driveshaft angle during vehicle operation, invite six friends for a drive and see if the vibration changes or goes away. I´ve had driveshafts rebalanced for less than thirty bucks (usually didin´t affect the vibration though).
I´ve also seen worn spider gears, create a pretty good moan. Sound usually changes with speed and when turning, when the sound/vibration is coming from the rear end. I´ve run a moderatly worn rear end, with a moderate groan for 60,000 miles. So I`d guess it isn´t a panic situation, but an indicator of a possible problem.[addsig]

 

[MudderChuck]

1076029

Forgot to mention, the easiest way to test for a slightly bent driveshaft. Buy a peice of one inch angle iron, cut to fit, between the balance wieght (usually near the end) and the yoke weld. Rotate the driveshaft in the V of the angle iron. A slight bend or ding can be spotted pretty fast.
I´ve had driveshafts modified/fabricated, and I´ve made my own using the angle iron technique and a MIG welder (no balance) that ran just fine, no noticable vibration. But probably accelerated the wear in the U-joints some.[addsig]