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Old 11-02-2011, 06:04 PM
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Originally Posted by 5 CWT
There is not a single man on the planet that can accurately dictate the degree of pinion angle for any given setup,it is all based on theory and previous trial and error usually more error!
I guess I'll have to take the time to educate you on this subject. Whether or not you listen is another story. After all you can lead a horse to water but you can't make him drink.

Driveline basics:

Drive shafts in rear wheel drive vehicles have "U" joints at each end that transfer the rotational energy from the output shaft of the transmission to the driveshaft and then from the driveshaft to the differential. All "U" joints rotate in an elliptical motion, unless the operating angle is exactly zero which is almost never the case. So, this means the "U" joint at the front of the driveshaft and the one at the rear both speed up and slow down twice per rotation. That's why they need to be installed "in phase". Each "U" joint must speed up and slow down at exactly the same time as the other. If they are not in phase vibration is inevitable.

Not only do "U" joints rotate elliptically, the ellipse changes as the angle of rotation changes. In order to keep from creating undue vibration the "U" joint angle at each end of the driveshaft needs to match the other as close as possible so the ellipse the "U" joints travel in are the same. In other words, the angle of the output shaft of the transmission and the differential pinion gear input shaft need to be in the same plane. This helps keep the rotational angles for both "U" joints equal. Differences here will create driveline vibration because as the rotational angle of the "U" joint changes the elliptical path changes and when one "U" joint travels in a different ellipse than the other, vibration is created. Also, the greater the operating angle of the "U" joint, the more distorted the ellipse becomes and the greater the torsional vibration. This is why most "U" joint manufacturers recommend an operating angle of 3 degrees or less. Operating the "U" joint at greater angles is possible but it will cause premature "U" joint failure and driveline vibration due to excess torsional stress.

In summary, for a street driven vehicle the transmission output shaft and pinion input shaft need to be in the same plane, (or parallel) and the angles need to be kept at 3 degrees or less for optimal longevity. Lower operating angles also minimize driveline vibration introduced by the elliptical rotational pattern of the "U" joints. Drag racing and specialized rear suspensions will require different settings but the "U" joints will still operate under the same laws of motion.

Consider yourself educated. Proper driveline angles, when it comes to "U" joints and driveshafts, are critical to effectively transmitting torque and power from the trans to the differential without creating vibration.


"One of the problems with stupid people is they very rarely realize just how stupid they really are." - Anonymous
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