I have the Superlift 4" that actually measures around 5 1/4" with adjustable arms f&r, tom wood cv drive shafts f&r and 35" KM2s on 2dr rubi. After many different adjustments my castor is at 2.8 with 1/8" toe in, this keeps the front drive shaft from vibrating and you can drive mine with one finger on the wheel. What seem to have the biggest effect on mine was tire pressure. The 35" tire can hold more weight with less air pressure than the stock 32" which causes the tire to round in the middle. I run mine at 28psi which gives it a good contact pattern when you do a chalk test. I have 37000 miles on the tires with no odd wear. The dealer can reset your TPS. With pressure at 32psi(this was as low as I could go without setting off the stock TPS setting) the steering was extremely darty. This is just what works on mine.

 

Naw, I used to work there a LOT. And my wife and I love it there so we used to go quite often. Haven't been in a while as there's a lot of the world we've yet to see.

 

I've been playing the same caster balincing game lately. I got the actual caster measurement from an alignment shop. It was 3.3° but they did not adjust.

At least now I knew my caster, so i measured my pinion angle and also right below the lower ball joints on the C. These angles I used as reference. I then lengthened my lower control arms to dial in +3° of pinion angle (~6.3° positive caster). This turned out to be way too much. Steering felt awesome, but the driveline vibrations were too much.

I backed it off to +1.5° (~4.8° caster). It steers okay, similar to stock and the driveline vibration is only slight at 50-60 mph. I think it is a good balance point.

By the way, I used an application on my iPhone to measure the angles. I call it an iPhone alignment.

Now having said all that... I'd love to go back to around 6° of caster. The steering felt great! Good on center feel. Good linearity. Good returnability. Almost no wandering or kick-back.

The problem is the driveline angles. So the stock driveline set-up was based on a geometry where the pinon was aimed directly at the transfer case output. Basically zero driveline working angle. So the CV joint at the transfer case output works well. Now with the lift, there is an angle at the lower u-joint to keep good caster angle.

My observation is with a 6° caster angle, the pinion angle is almost parallel to the ground. Also, the transfer case ouput shaft angle is almost parallel to the ground. With this geometry, a single u-joint set-up on both sides of the driveshaft would cancel eachother out. Therefore, reduced or no driveline vibration.

I have sent an email to Tom Woods asking if they've investigated this and if they'd be willing to build me a custom shaft with this set-up to try my hypothesis. I'll let you know what they say. I might try my local shop too.

 

Cool! I just got my jeep back from the alignment tech.
Specs: castor-> 4.7 driveside 4.4 pass side
Toe-> .15 both sides
Camber-> 0 both sides

Impression: handles well enough to let my wife drive it. No vibes. My top speed today was 65mph. I'm tempted to raise the caster a little over 5, but I don't wanna push my luck. The DS angle is starting to look steep.

 

I'm running approx 6 degrees castor with 4"lift,teraflex adj lowers,stock uppers and tom woods front shaft,no vibes and drives much nicer,just like eDiveBuddy says,I kept adding castor,one turn at a time(last time I measured I was 5.5 have added 1 turn still no vibe)then more positive castor I add the better My JK drives,was at 3.0 degrees stock drove terrible especially on the highway

 

If decreasing the front uppers is the best fix but usually not possible to go far enough.....How come the TF instructions say to lengthen both uppers from 18.75 to 19.5 and lowers from 22.5 to 24.0 or so ?

These stats are for 3" lift 4 door?

 

Talked to Tom Wood about our problems with getting enough caster for good steering geometry vs. driveline angle and related vibrations. As I suspected we need matching joints at each end. Single u-joints don't provide enough working angle for full suspension stroke of these vehicles. So the answer is a "multiple double cardan drive shaft" .. in other words double cardan joints on both ends. Since they are both constant velocty joints, this should eliminate vibrations at the working angles we need to get 5°-8° of caster.

I measured my flange to flange length last night and am ordering the multiple double cardan shaft from Tom Wood's today. I'll update everyone once I get it installed.

 

OK... Trying to learn as much as I can about caster reading these threads and get mine set to the optimal angle.

My setup is 2.5" TF coil lift + 3/4" front spacers on 33" tires. My alignment numbers are below and based on what I've read I would benefit from adjustable lower front control arms and 5-6 degrees caster...sound about right? Please advise

 

Yup. I think you've got the right idea.

 

So approximately what length does the control arm need to be to get to this angle ?