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Old 08-27-2010, 09:49 AM
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AxleIke AxleIke is offline
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Join Date: Apr 2006
Location: Arvada, CO
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For those that are curious:

When one lifts a truck, with regard to drive shaft joints, there is an easy way to figure it out.

With a single cardan style, which is just your standard shaft with u joints at each end, all that matters is that the angles at each end are the same. To briefly bore you, angular velocity must be conserved throughout a spinning system. In the case of angled shafts, like a drive line with single cardan style joints, angles cancel out. Thus, if you have a 25 degree angle on your first joint, you MUST have a 25 degree angle on the second joint, in the opposite direction. This will conserve angular velocity as it is a vector function.

If you lift the rig, and the angles change the SAME amount, then you will be fine. If they are different angles, say 25 and 15, then you need axle shims or a cut/turn for the front.

The double cardan, or CV joint, is nice, because it does exactly what the name implies, constant velocity. Angular velocity is conserved through a double cardan joint, which means that you don't need a second joint to cancel the angle out somewhere else down the line.

Since driveshafts have a second joint, with a CV jointed driveshaft, you must point the pinion at the transfercase so there is an angle of 0deg in the joint. Actually, with leaf springs, you generally want to point the pinion down about a degree or two to accommodate axle wrap when under load.

Both systems work quite well. IMO, the CV style is a better way to go, simply because you get to rotate the pinion up, which gives you more ground clearance, and gets the pinion up higher, allowing for less chance of a rock contacting it and trashing it.

I know this is all probably yesterday's news to most, but I figured I'd throw it in, in case someone was reading this down the road and had no idea what the reasons were.
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