(Yes, there are MANY write ups already, and even videos on YouTube on this already… I just decided to do one anyways…)
Here’s my write up for the installation of the new front driveshaft on my JKU (double-cardan). I went with Tom Woods since I had a good experience them him/them for the 2010 JKU. Prior to ordering a custom driveshaft, you will need to take accurate measurements and provide them when ordering. If you visit Tom Wood’s website, it will tell you exactly how to measure… but in short, you’ll need to measure from the face of the flange at the diff to the lip of the flange on the transfer case side. However, you will want to do this AFTER you have installed your lift, not before (this includes installing upper/lower control arms and dialing them in as best you can).
I ended up removing the front driveshaft during the installation of my lift kit, and drove around town with rear wheel drive until the driveshaft came in. I had to do this because of the severe angle at the transfer case output after the lift was installed. Also, since I opted to not use an exhaust spacer, I would risk the driveshaft coming in contact with the crossover pipe just driving around town. Because I took off the driveshaft early on, I don’t have pics of the factory setup…
Removing the front driveshaft is pretty straight forward. I opted to remove the driveshaft from the diff first, then used a jack stand to hold up the shaft while removing it from the transfer case side. You’ll have more room if you remove the t-case skid plate as well. While the diff side was rather easy, the t-case side requires a little patience. If you’re doing this by yourself, you’ll see why I opted to remove the diff side first. In “Park” and 2WD, the front driveshaft will spin loosely. To lock it, simply pull it into 4WD Hi. This will lock the shaft so that you can break loose the bolts on the t-case side. As you need to, slip the t-case into 2WD, turn the shaft to where you need it to access the other bolts, and lock it back up by putting it into 4WD. The driveshaft is heavier than it looks… so I wouldn’t recommend laying right under it when taking it off.
Once the stock shaft is off, it’s time to remove the pinion nuts. This part isn’t fun, at least the front. I don’t have a powerful enough impact to break these loose, so out comes the LONG cheater bar with the assistance of a floor jack (for the pinion nut at the diff). Also, be sure to set the parking brakes and chock the wheels to prevent forward movement (it is easier to do this with the tires on, and the Jeep on the ground on its own weight—but as you try to loosen the pinion nut, you’ll end up moving the Jeep slightly forward). Any forward movement of the Jeep is wasted efforts on getting the pinion nut loosened. Once the nut is off, you should use a 3 jaw gear puller to help with the removal of the factory output flange. It is on there REALLY tight. Here’s the front flange removed:
Next I removed the t-case output flange. This nut was easier to remove, and I was able to break it loose by hand with the cheater bar. Be sure you have the t-case in 4WD, otherwise it will just spin. Oh, by the way… Tom Wood’s instructions say to have a 1-1/8” socket for the nuts. The front was 1-1/8”, but the t-case took a 1-1/4” socket.
Once all this is off, it’s time to prep the new driveshaft. Remove the bolts that attach the new outputs (flange and yoke) and inspect the flange surface to make sure it is clean and smooth—no dirt, no pits. This mating surface needs to be completely flat.
While Tom Woods does a good job of pre-lubing all the joints, it is a good idea to ensure they are fully packed with grease, especially the hard to get to fitting in the double-cardan joint:
I opted to wait on greasing the slip yoke (the part where the 2 parts of the shaft meet and slide back and forth) until after it was installed:
Next, I installed the t-case output yoke. Following Tom’s instructions, I used blue RTV on the inside of the yoke, and I opted to put a little grease on the outside:
Carefully slide on the yoke, and the RTV will be pushed out to create a “seal”:
Tom provides 2 nuts with their driveshaft.. one metric threaded, one standard. Use the nut that fits. Tighten the nut to 160 ft lbs. Be sure to use some red lock-tite on the threads of the nut to help keep it from loosening up. I then installed the front flange, re-using the factory pinion nut, and using the same procedure as the t-case side (RTV, grease, lock-tite, 160 ft lbs):
Once that is done, it’s time to install the shaft. I installed the t-case side first, and used a jack stand to support the diff end of the shaft. I used the whole 2WD, 4WD method to turn the t-case output as needed and to lock it in place. Don’t forget to use red lock-tite.
Then I moved on to the diff end. It was a bit of a challenge to pull/extend the shaft, so I cheated and used this opportunity to pump grease into the fitting—as grease gets pumped in, it extends the shaft (at least it did for me). Using red lock-tite, I tightened up the bolts.
After this is all installed, I then had to dial in the front control arms. This is where you need to make your own decision, as I will not be responsible for any possible damage to your Jeep. I decided that I am not ready to drop the money for a Pro Rock 44, nor do I want to have the C’s cut and re-welded to “properly” correct caster and pinion angle. I don’t want to make this into a novel, but I suggest you search the web to learn about caster and pinion angles when using a single u-joint at the pinion and a double cardan at the t-case. Basically, this type of drive shaft is “optimum” when there is 0 degree difference between the pinion and the shaft (a perfect straight line). To have this on my JKU means I would have to turn the pinion up to where I would have -1 degree of caster. This is not “optimum” for steering and how the JKU tracks on the highway—in fact, it will become quite flighty on the highway and would need constant driver input to keep it going in a straight line.
I learned that 3 degrees is the absolute maximum angle for the pinion and shaft, before you enter the danger zone of either the shaft giving out, or the t-case exploding from the severe vibration. I decided to end with 2 degrees of angle at the pinion in relation to the shaft, which gave me 1 degree of positive caster.
No, this is not the “optimum” setup, but it’s a decision you’ll have to make as to what you would rather have. Personally, I can live with a slight driveline vibration at highway speeds if it helps me keep the Jeep going in a straight line. Just make sure you use an angle finder to REALLY make sure you are not past the 3 degrees of angle between the pinion and the shaft. (This is something I learned from the web, and from different sources, and seemed to be the most consistent.)
In case you’re wondering, I was able to learn that there is 6 degrees of separation on our JK’s.. meaning, if the pinion angle is parallel to the ground (90 degrees), the caster is at 6 degrees (positive). Our JK’s are best at 4 degrees of positive caster, which means with the factory setup, the pinion angle is turned up 2 degrees (88 degrees). This basically means I am 3 degrees off from “optimum” in regards to caster, but the exchange is that I don’t grenade my t-case.
Down the road.. perhaps 2 years from now, I’ll look into the ProRock 44 to have the “proper” setup.
After driving with this setup for over 3 weeks now, and hitting 80mph on the highway (our speed limit outside the city is 75mph), I’ve only noticed a slight oscillating vibration between 65 and 68 mph in the steering wheel that wasn’t there before (but then again, I was driving with only a rear driveshaft after I installed the lift kit).
And, for those that are curious... at full drop of the driver's side with the sway bar disconnected (shocks fully extended), I have 1/2" clearance between the driveshaft and the exhaust crossover. Oscar has RK's 3.5" Mid-Arm Flex lift (not the Plus, not the X-Factor), and I have Bilstein 5100 series shocks (Quadratec part# 16070.2001). I haven't measured the length of the shock when fully extended, but I need to for future reference..