The major difference between...
The major difference between J.E. Reel's new driveshafts and the JK's factory driveshafts is the CV joints. J.E. Reel's 'shafts utilize U-joint technology, while the OE driveshafts use Rzeppa CV joints. The new driveshafts are constructed from 2.75x0.095-inch DOM (drawn-over-mandrel) steel tubing in the rear, and the front 'shafts are made from 2x0.0120-inch DOM steel tubing.
If you aren't familiar with your new Jeep JK's driveline system and would like to learn a little something about it, then please read on. The all-new Jeep Rubicon is an extremely capable off-road vehicle. Some people say it's even more capable than the TJ Rubicon in factory form, but as the old saying goes: Nothing is perfect. One of the very few mechanical issues the JK has is that Rzeppa CV (constant velocity) joints were used on the drivelines.
This joint was invented in the '20s by Alfred Rzeppa, a Ford Motor Company engineer. This style of CV joint was created for smooth vehicle operation and is more fitting for a car or luxury SUV. The major disadvantage of this type of CV joint is that it isn't designed to run at an increased operating angle. The result is that the joint's life is greatly reduced, and complete failure of it is quite possible under harsh conditions.
Like the Jeep Grand Cherokee and other Chrysler vehicles fitted with Rzeppa CV joints, if the vehicle is going to be left in factory form and driven mainly on the highway or used for mild wheeling then the OEM driveshafts should be just fine. If the vehicle is going to be modified with a suspension system that gives the Jeep an increase in ride height, then serious thought should be given to new drivelines.
The problem with the Rzeppa-style driveshafts is that they cannot stand up to the stresses of torque load at angles different from what the factory designed them for. This is especially true if the suspension is flexing and articulating off-highway. There is only about 3/4 inch of movement from the center of the Rzeppa joint (shaft) to the edge of its housing before the shaft makes contact. When the vehicle is lifted, articulated, and flexed, the shaft in the factory CV joint will make contact with the housing and start cutting into the retainer strap, rubber boots, and seals.
The Rzeppa CV joint comprises an outer housing, an inner race (multicross grooved or tracks), balls (large bearings), and a cage (bearing cage). The inner race is the center of the joint, the balls sit in grooves on the sides of the race, and these are held in place by the cage. All these components fit neatly inside the housing, but the balls of the joint are very close to the edge of the housing. If the vehicle hits a large bump or obstacle, or a wheel drops into a large hole, forcing suspension compression or droop, the balls can be forced out of the front or backside of the CV joint. This basically mean the joint has failed, leaving you stranded on the trail.
 The factory driveshafts are...  The factory driveshafts are great for everyday driving and mild off-highway conditions. Anything extreme will push the limits of the shafts' capabilities. |  This is the Rzeppa CV at the...  This is the Rzeppa CV at the rear axle's pinion. If this angle of the driveshaft was forced anymore under extreme conditions, the housing would more than likely cut into the rubber boot (seal), consequently contaminating the joint's grease. Water and grime wreak havoc on a CV joint's internals. |  At the output of the transfer...  At the output of the transfer case for the front and rear, the new driveshafts use a double Cardan joint. In basic terms, the double Cardan joint is two U-joints held together by a center housing. Attached to the U-joints are yokes: One side is attached to the driveshaft, the other to the output of the transfer case. The joint works smoothly without binding at driveshaft angles more extreme than factory. |