Just put in some new 3 1/2" rear leafs today and I get a vibration and humming noise steady between 15-30mph. After 30 it goes away. It sounds like maybe the rear driveshaft u-joint may be binding? From what I've read I thought if you went 4" or higher you'd need a t case drop or SYE. The noise wasn't present before the new leafs. The ones I removed were the factory leafs with an add-a-leaf that didn't do much good. Searching forum didn't turn up many results for what I needed. Most people were having vibrations between 30-40. Mine are at lower speeds.

 

You need to measure your driveline angles to know. How much lift did you actually get? Sounds like driveline vibes but could be something else. Some people have had to compensate with a TC drop/shims or SYE/shims with under 3" of lift. Part of lifting.

 

The difference between before and after is around 2". I gotta see how to measure the angles I have now.

 

the u-joints aren't used to running at that angle now.

you should be able to get away with a 1 inch t-case drop for now till you go bigger. then a sye may be needed.

i'm at about 7.5 inches and i have no sye or drop and i have no vibes. but i do have a modded drive shaft yoke.

 

So it's just them complaining then. I'll look into doing a 1" t case drop and see if that helps. Since the rear is almost 2" higher than the front now I was looking at adding a spacer on the front springs to level it out some so that might bring the rear angles down some as well.

 

X2 , every jeep is different.
My jeep is fine as well up to 6" but I've modded my drive shaft length & swapped U-joints.

 

Ordering a 1" t case drop this morning. Hopefully that will suffice. I really don't plan on going taller in the near future. If I can find maybe a 1/2" to 3/4" spacer for the front that would be plenty for the lift I already have on it now.

 

sounds good. you should be all set once you get the t-case drop and coil spacers in.

i modded my rear drive shaft using a yoke from a yj. it has better clearance for steeper angles.

 

So what kind of dumb@$$ery is this? The back side is a bolt and the front side is a stud welded to the unibody with a nut on the t case side. And my luck the passengers side bolt broke leaving just the threaded stud so I can even put the t case drop in now. There are no other holes I can see that would be usable. So what now?

 

PB blaster and a small pipe wrench with a cheater bar.

 

For what? There's nothing to get a wrench on. The stud doesn't move cause it's welded in I'm pretty sure. No opening from the top to get to it either. The one that's broke is broke off flush with the unibody. I may have to weld a head onto it and see it if comes out then. It was turning when it broke cause I got it turned about 3 revolutions before it snapped.

 

My thought would be to use a punch and a BFH to push what's left of the bolt out by breaking the threads, then "fish" a new bolt with a lock washer up into the unibody rail and drop it into the hole you just created, and use it kind of like a stud. Pretty much the same solution people use if they break one of the upper shock bolts for a rear shocks. Hope it makes sense the way I said it.

 

just lifted my jeep with a add a leaf.also did shackels.did not want to but the factory shacklesfellapart.it was labor day had to do aftermarket.also did the bigger springs in front.any way bad vibes.cant drive it.bought shims to do rear forpinion angle.wanted to drop case but the first bolt snapped.so I leftthem alone to soak in PB blaster.would like toknow how to fix this problem with the broken bolt....

 

The stud is not welded from factory. It's just threaded into a welded nut and tends to get super rusty.

 

Double-nut the stud and spin it out.