sounds like u joint roll over to me. double check your angles as mentioned above. Now that she is sitting on the ground, go ahead and re-torque everything. drive it a tank of fuel, and then retorque again. always torque everything with the weight of the vehicle on the ground.

 

Thanks Dexy (no, I'm NOT going to call you Sexy!). I understand about the TC output and diff input needing to be parallel. What I'm not sure about is how those lifted springs would have put them out of parallel (if that's what's going on). The axle mounts on the stock springs and the lifted springs both appear to be the same angle, and just vertical lift shouldn't affect that.

But here's my theory; nothing is perfect. There is some minor amount of unparallelism (is that a word?) between TC and diff, even in a bone stock car. When you increase lift, the effects of that same minor unparallelism are exacerbated due to the increased input and output angles. Sound about right?

 

This is a great vid explaining what happens when you change the angles.

 

Re is known to give about an inch or so over advertised. They don't settle too much from what I've read.

 

Yup Ronin, I completely understand driveshaft alignment and phasing. What I don't understand is how lifted springs affects that. Assuming the lifted springs hold the axle and diff at exactly the same angle as the stock springs did (which seems to be the case), simply lifting the back shouldn't induce driveline vibrations.

 

Yep my RE 3.5" springs ended up right at 4.25" of lift and havent budged since install.

Lifting the rear causes the rear end to move further away from the t-case. That means it pulls the slip yoke further out of the t-case since your driveshaft is still the same length. The further out it is, the more its going to cause vibes. Plus the angle of the driveshaft will increase further helping create vibes.

 

It's likely the arch of the leaf spring that has changed the pinion angle. That is why some will use the wedges to get the pinion angle back to alignment with the output shaft angle. But that works only to a point where a SYE/CV is needed, as the joint angles are just too harsh for a two joint Driveline.

 

This. Lifted springs will change the angle of the yoke on the diff, throwing it out of alignment with the yoke on the output of the TC. The shims help point that diff back up towards the output shaft of the TC. Check the angles on your yokes, they need to be within 3* of each other for proper phasing. Adding a SYE and double cardan shaft helps this, but you still need shims in some cases. I had to use 6* shims on mine. The higher you go, the more shim angle you'll need. I'm at 5.5-6" on RE leafs.

 

This is true for the most part....but if you have the weight of the jeep on the axle housing (like as in the jeep is sitting on jackstands under the axle), that will give the same result.

The big problem is if you tighten the ubolts or control arm/shackle bolts when the weight is being supported by the frame vice the axles.

it is better to have the jeep on it's wheels on the ground, cuz you can roll it back and forth some to ensure everything is seated better then torque it, but as long as the weight is on the suspension, you'll be good.

 

Man, if it ain't one thing, it's another!

So I picked up a RE Xfer case drop kit, just a minor one with 1/2" spacers and bolts. Got under Frank prepared for a simple job, and this:



Same thing on both sides of the crossmember, one fastener is a bolt and the other is a nut on a stud. Of course that stud goes into a hidden, unaccessable channel so I hve no idea what's on the other side. And the stud isn't long enough to take a 1/2" spacer.

What's going on here? The kit contains 4 bolts, how am I to deal with the studs?

 

double nut it and pull the stud out.

that is normal

 

The reason this happens is two fold. One is that the shackle angle changes, causing the rear of the spring to go down. This changes the driveline angle 1° for every inch of change there. The other is that the spring center bolt, and axle position is not centered on the spring. When the spring is flat, or near flat the spring perch is roughly parallel to a straight line from eye to eye. When you introduce arch into the spring, the spring perch ends up not in the center of the arch, but in part of the front arch of the assembly relative to the center. The two combined can change the pinion angle by as much as 4° on most lifts

 

As in ... it's a double ended stud and the other end is threaded into a welded on nut inside the channel? Or do I literally pull the stud out?

 

Goes into a welded nut inside the rail.

 

double nut it and it will come out.......just like a bolt (unless it's rusted in)