pcmasten

I have a 09 4dr JKU Sahara w/ a rubicon front axle and a 3 1/2" metalcloak lift. I am running 35" tires at 30 psi. I initially installed the lift to metalcloak specifications for upper and lower control arm lengths (which should have given about 5 deg caster). I also have had the front driveshaft replaced. This gave me somewhat flighty steering and a low rumble / vibration at 70mph. While I have lived with this for a while, I'm heading out to Ouray for some jeeping and would like to solve this before my 1200 mile drive. I just measured the angle of the front differential at the flat spot (with a hole) and measured 3.3 deg. I am assuming that this flat spot is parallel to the flange. I plan on adjusting the UCA's to achieve 6 deg on the differential flat spot.
I just wanted to confirm that I am on the right track here with my measurements. I haven't had an alignment done recently, and the tire wear is good and the jeep does not wander.

resharp001

I woundn't assume anything. To be honest, even on a garage floor with zero slope per digital angle finder, I still found measurements at the pinion flange to be over 1* than the alignment machine read. If you're getting a "rumble" after the new DS, I'd lean more towards you have too much caster and it's jacking with the DC DS than too low caster. Just my opinion, but I'd get a reading from wherever you feel good about...as a baseline. Then, go get an actual alignment reading and make adjustments from your baseline. IE, just adjusted as the difference from your baseline reading in the garage by whatever you feel like you should adjust by off the actual spec.

ronjenx

The best way to adjust caster is to get an alignment check done, then keep track of how much you change it at home. (What Resharp001 said; condensed version.)

Regarding your vibration at 70mph, keep your speed below the point of vibration until you get it figured out.

This is what usually brings on a front T-Case explosion:

Lifted
Re-geared

Double cardan at the front of the t-case

Adapter on the t-case front flange, rater than the shorter replacement flange

More than a couple degrees from straight between front pinion and front drive shaft

Highway speed

Vibration (whether perceived or not)

Another factor is lack of lubrication in the front double cardan. This can cause the same result without any of the other factors.

Seizer

That’s some for food for thought there. My factory drive shaft rzeppa went kaput so I replaced it with an Adam’s. I’ve had the Jeep do up to 80mph and I swear there was the tiniest vibration that used to not ever be there. I thought it was tire vibration due to the road surface because it’s ever so slight. How do you check your pinion angle for proper alignment? If I eyeball it looks fine to me, meaning I don’t see a weird angle between the pinion and DS. By adapter I assume you mean something that mounts into the stock JK rzeppa housing? The Adam’s came with a new flange that I had to put on the T-CASE.

resharp001

Think about this.....1* change in caster is a huge amount. Is your eyeball calibrated to the point of seeing 1*? I mean, when using a non-digital angle finder I can barely even read the 1* slashes. When using a digital angle finder on a pinion flange, depending on where you place it on the flange itself you'll get varying readings. My point just being that these aren't things easily seen by our eyes. It's great to use an angle finder at home if you know what the true reading off a machine is. I got a "lifetime" alignment at my local Firestone years ago. That $140 (at the time) has more than paid for itself. Down here you can usually roll in for an alignment and even if you opt to not have them make any changes (those places can only center the steering wheel and set toe) they will give you the print out. Now, nothing is free......I swear they take 90 minutes cuz they go over your entire car looking for anything that could be replaced or serviced and then suggest that to you.

Seizer

Copy that, I’ll take it in to local Jeep repair where they will adjust things for real not just toe and such.

resharp001

Probably different with an offroad shop. The normal alignment shops usually charge additional fees to adjust control arms, and that 1) usually isn't worth the amount charged, and 2) means some dude working in a Firestone garage is messing with my suspension. Both things I like to avoid if possible. I guess I prefer to monkey with my own jeep.......that way if something happens or i forget to torque a bolt there's no one to blame but myself.

If you do take it somewhere to dial it in, definitely double-check the torque on your control arm bolts and jam nuts. Here's food for thought Chris.......Every bit of money not spent on someone twisting your upper MC arms a rotation one direction or the other, is money that could be put towards a skid plate which would give you bit more peace of mind.

pcmasten

Well, I just got the alignment on the Jeep done. 3.8* LF and 4.0* RF. That gives me a starting measurement using a digital level on the diff. While the low angle (assuming 6* is optimal), would explain the "flightyness" of the steering, it doesn't explain the slight (or low) rumble that I hear/feel at 70mph. After re-doing the angle, I'm considering pulling the front driveshaft to see if that eliminates the problem. Do I need to pull the entire ds, or just disconnect at the diff and tie it up so it doesn't fall off?

resharp001

Don't assume 6* is optimal, it is not. 6* is just what is built into those factory axles. Most us lifted guys reside in teh 4-5* range. From factory it's 4.2*. I'd shoot for 4.2 - 4.5 to start. I'm a little surprised. I thought maybe your caster was too high and that was resulting in the driveline vibes.......that is the common issue with too high caster and a DC driveshaft. Though it's convenient to be a little lazy, I'd remove that DS entirely to test without it. Error on the side of caution and don't chance it. Even something as stupid as whatever you have holding the DS up coming undone and allowing the DS to fall to the ground could theoretically happen.

Seizer

I hear ya man. I have no issues crawling under there and giving the control arms a few turns. My thing is how do I know I set my angle correctly without the tooling to measure these things. I’ll call Adams and see what they have to say.