I'll try to explain...


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Posted by Dan Shockley on Monday, December 27, 2004 at 9:52PM :

In Reply to: Math Help, Driveline angle posted by MoparNorm on Monday, December 27, 2004 at 4:54PM :

Well Norm, there are several issues. First of all, the 16 degrees comes from the maximum articulation of a joint and transfer of power. Most spice joints begin to make metal to metal contact at about 25 degrees. In addition, as the angle increases, the torque on the joint increases(given the same input torque). The 16 degree figure normally is quoted based on the ability of the joint to transfer the power applied and this is generally a good number for off-highway applications. We have also seen multiple driveshaft joints developed over the last couple years that allow upto 40 degrees of articulation. This again is based on transfer of power.

Now to understand Dana's comments. A driveshaft between two ujoints, with any angle between them does not travel at a constant speed. If the input on a driveshaft is driven at a constant speed then the driveshaft will accelerate and decelerate as it rotates. This is true because the yoke is traveling in an eliptical path. The amount that the driveshaft accelerates and decelerates is a function of the angle. The greater the angle the greater the change in angular velocity. If you match the input and output angles, and install the u-joints "in-phase" then the input and output yokes will move at the same constant speed, while the driveshaft speeds up and slows down every revolution of the shaft. In-phase means that the yokes of the driveshaft are lined up in the same plane. If you want to better understand this phonomenon, take apart the driveshaft on your jeep, rotate the yoke 90 degrees reinstall and take it out on the freeway. It will rattle your brains out. The reason that Dana warns you to stay away from excessive driveline angles is because as speed increases and as drivelines become excessively heavy, this acceleration and deceleration of the driveshaft can be felt as a vibration elsewhere on the truck. They are being cautious and trying to protect themselves from being the blame if someone experiences a vibration.

Just remember, keep those input and output yokes parallel, keep the u-joints in-phase and minimize the angles. It will probably work, but you may suffer from short u-joint life.

I hope this helped a little,
Dan



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