00t444e

My jeep has a vibration between 20 and 25 MPH it goes away when coasting at that speed and starts when I give it gas, it completely goes away at 30 MPH or above. Is this the normal driveline vibration associated with lifting the rear? If so will a T-case drop fix it? I don't plan on lifting it anymore so I don't think I need a SYE.

Martlor13

it probably will. But an sye is still recommended. A t casr drop is a bandaide. Itll eat your mounts

DCox

I second the T-case drop eating mounts. The PO of my jeep had a T-case drop installed when he paid like 5 grand getting the jeep lifted and putting tires on it. I couldn't understand why when he was spending that much money he didn't bite the bullet and get the SYE as well. Anyways fast forward a year and a half and I buy the jeep. By this time vibrations had gotten so bad the guy couldn't sell the jeep for much so I got a great deal. Had to do an SYE, shim the rear axle, and replace all mounts(they had gone to total mush). Now I'm vibration free and loving the jeep. If you were to do a t-case drop please do it only planning to go to a SYE in the very near future or you can end up causing yourself more work and cost in the long run.

4.3L XJ

The late XJs tend to vibrate with just about any lift. The yoke on the tcase gets pulled out too far and it wobbles. A drop usually fixes it, but the slip yoke eliminator is a much better option.

neverenuff

is your 8.25 pinion pointing straight to the transfercase output shaft? do you have degree shims installed under your leaf springs? your sure this is a rear end vibe and have ruled out the front end from vibrating? 242 transfercase is limited when trying to install SYE , I believe hack and tap is all that is available...

00t444e

The springs have shims built in to them, I am pretty sure it is the rear causing this because it only does it when I am on the throttle. It goes away when coasting.

neverenuff

transmission mount or engine mounts that are mushy or torn will cause bad driveline angles on acceleration. I would give'em a good look with a flashlight. If you have not done it yet, regardless I would pull the front driveshaft and test drive... just make sure all variables have been checked.

00t444e

I can also hear it popping from the rear when taking off on a hill. Today I had a trailer hooked up and it was much worse. I think it may be the rear driveshaft u-joints.

investinwaffles

SYE is really the best way to do it, you can get a Hack n Tap kit for $100, install tools for about $50, and a junkyard driveshaft for $10-$50 and be good to go for about $200

Install in about 3-4 hours, like a 2 out of 5 on the difficulty scale.

00t444e

What driveshaft do I use and what special tools do I need?

investinwaffles

Crud, I didn't see you had a 242 t-case, it costs a bit extra because there is a rear tail-housing cover that you need to replace with a shorter one in the kit. According to IRO;

http://www.ironrockoffroad.com/10109.html


You basically measure, cut the transfer case output shaft in the rear, drill a 1/4 pilot hole and then a 5/16 final hole to tap with a 3/8 tap. Then, you bolt up the tail housing adapter, flange adapter, and finally your driveshaft.
Afterwords, you will likely need to measure the pinion angle and add some cheap spacer shims that vary from 2-8 degrees (it basically angles your rear axle upwards so the angle to the t-case matches what it was before the lift)

EDIT:
Video which explains the process;

xj_bill

Yes I would inspect all u-joints first...they can easily dry out and rust, and this is the type of behavior they exhibit when they do.

I just replaced my rear driveshaft u-joint...unfortunately mistook it for a bad pinion angle in the rear...by the time I had realized it was the u-joint a bit of damage had been done to the input shaft to the rear axle, not catastrophic but certainly more damage than I would have liked.

00t444e

I replaced the u-joints and the popping went away but I can still feel the vibration.