This begs the question (which ron has already broached):

Are we seeing a similar number of t-case failures on bone stock JKs?

If it's happening, it's not being reported here, and the disparity can't be attributed to guys not using their stock JKs on the trail; there's a thread elsewhere on the forum devoted to JK owners who wheel stock.

 

This is a very informing thread. It definitely has me thinking about my drivetrain. I experience slight humming/vibrations around 45 mph. If I go 5 below or 5 above that I don't get them.... I'm wondering if I'm doomed to have this issue happened to me? I looked at the spyntec writeup from the link that was posted. Someone else had replied saying that it only worked with 5 to 5.5 backspacing Not sure, but it sounds like a great idea. Where can I go to actually buy the tool to check my caster angle?

Thanks, I'll be subscribing to this thread.

 

What do you have for front drive shaft? Double cardan at the t-case, and single at the pinion?

 

At $1,450.00 a set, Spyntec hubs are prohibitively expensive IMO, and do nothing to address the underlying issue. And you do have to purchase new wheels and either new (or modified existing) rotors. No thanks.

It's simple then. When you are under 5 degrees caster, does your Jeep scare you or handle in such a way that you would be worried about letting your wife drive it? If not, and if under 5 deg caster eliminates your vibration issue, problem solved.

The tool to check your caster angle is not a six dollar angle finder from the hardware store, but a well reputed alignment shop. Before someone comes in here and tells me how "accurate" their angle finder is, please save it; most shops use machines which measures to .01 degree accuracy.

(For the record, a dial indicator is fine for the installation of your new front control arms before driving to the shop for final measurements/adjustments.)

 

And it's not a direct measurement like an owner at home would be apt to do.
There is no "pad" upon which to place the home angle gauge.
It involves turning the wheels left and right and deducing the caster angle.

 

I'm seeing the same sort of vibration at the same speed. And yes, mine is double cardin at the T Case and a single to the front diff...

 

I'm going to go out on a limb here and guess your caster angle is 6-7 degrees per the write-up? (That's significantly more caster than factory spec of 4.5 degrees, for what it's worth.)

Before I was able to wrestle nearly a thousand bucks from my conscience for new drive shafts, I spoke directly to Tom Woods. I doubt there is a man in the industry who knows more about drive trains than he does.

Woods was clear: a double-cardan at the t-case helps, but is no panacea for excess caster and the fatal vibration it can bring about.

He told me to run at or under factory spec or assume risk to expensive drivetrain/powertrain components.

I drive back and forth to Colorado 2x a year and I run 75-80 mph nearly 1,000 miles (one way!) for our annual Moab outing in the fall... and I have yet to suffer white knuckle fear over my JK's handling.

 

I haven't had the time nor the money just yet to replace anything from stock. Right now I'm running with the AEV/Nth degree 4.5" lift. The caster is supposedly put back close to factory caster when the LCA brackets were bored out and then set slightly farther back towards the rear....hopefully this is making sense I do plan on getting a Tom Woods front DS to replace the front and plan on upgrading my front axle.

 

Wow, thanks for the input from everyone. That was really fast I honeslty don't know what degree of angle I'm at with my caster. As it drives right now, my rig handles very well on and off road and up at higher speeds. I've never had an issue...(knock on wood) with the way it feels on the road. I am planning on getting new adjustable LCA's for the front....I'll probably have to take it to a shop and have them dial it all in. I'll have to check back and see what the correct degree of caster should be....I can't recall if it was stated on this post or another....Thanks again!

 

I agree with what he is getting at. But I believe he is indirectly referring to excessive pinion angle, which would be the source of the drive shaft vibration.
With the double cardan at the t-case, the u-joint angle at the pinion must be extremely close to ZERO. (drive shaft axis in line with the pinion axis.)

Dynatrac asked for input from JK-Forum members, and designed a front axle which has the pinion angle raised, but kept the caster close to stock. This will allow the front u-joint angle to be much closer to zero while having a non-compromised caster angle.