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Old 08-27-2010, 08:40 AM
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Air Randy Air Randy is offline
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Location: Franktown, CO
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Quote:
Originally Posted by nuclearlemon View Post
i don't know anyone who required a dc shaft with the lift because the ujoint angles don't change.
It's impossible to effectively raise the frame (or lower the axle if you prefer) 4" and not also increase the angles on the U joints unless you somehow lower the TC at the same time. That said, as long as you stay within the working range of the yoke/u joint from full stuff to full droop you can run it that way.

To be clear, a DC shaft is recommended ONLY when you rotate your rear diff up so the pinion points straight at the TC and the angle on the rear u joint is 0 degrees. I know, 0 on the rear and less angle on the front would seem to be a good thing. But go read any technical discussion on the topic by numerous drivetrain experts and they are unanimous in their recommendation. Apparently, when your diff is not rotated and you have angles on both top and bottom u joints, they offset each other since every time the u joints rotate they move the DS slightly off center. When there is 0 angle on the bottom joint (pinion rotated) the top of the DS moves off center while the bottom one does not, thus you lose the offset and get the same effect as an out of balance driveshaft on the top of the shaft. Over time, depending on severity, this can reduce the life of the u joint and increase the wear on the output shaft of the TC.

I drove mine like this for awhile and it worked OK but I could feel some vibration at hwy speed. If the slip splines on your shaft are worn you'll probably feel it more. Since I needed to get my DS lengthened anyways I took it up to Rocky Mtn Driveline. They looked at the setup and agreed DC was the right way to go. They lengthened my stock DS and added the DC joints on top for $200, so it wasn't much more than just getting it lengthened. I now have zero vibration.

If you keep your pinion in the stock location you DO NOT want a DC shaft as it will have the opposite effect and cause vibration.
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