I have a 2000 XJ with a 3" lift on 31"s. Other than that it's stock.

I'm trying to diagnose a few things on my Jeep. At low speeds/ low RPMs (under 25 mph or so) there is quite a bit of vibrations. I'm not sure if it has anything to do with the gears/ axles since I have lifted the Jeep?

I've been told that my differential needs to be rebuilt (by a shop that looked at it for me). At highway speeds when I let off the gas there is a grinding noise that I can hear coming from the rear end.

See the attached picture of my axle below, I think the front is a Dana 30 and back is a Chrysler 8.25. (Correct me if I'm wrong) Is this the best configuration for what I'm running? How can I tell what the gear ratio is and is there a different ratio I should use if I need to have the differential rebuilt anyway?

Am I on the right track with any of this or is it something totally different? Please help me out.

 

Also this is my daily driver, FYI.

Thanks.

 

Since you have a late model XJ, the t-case is sealed, and will not leak if the rear drive shaft is removed. I would pull the rear shaft, put it in 4WD high and drive it (be careful) and see if the grinding noise goes away.
Also, later model XJ are more prone to have vibes when lifted even a small amount.
A slip-yoke eliminator/HnT should help if not rid of vibrations while driving.
Stock, if you have an auto gears are 3.55, manual will be 3.07 gears.

 

is this your daily driver? if so, drop the t case, and get the rear shaft re balanced, i had an 8 inch lift on a 99 with a t case drop w a properly balanced driveshaft and no vibes, at all

 

hows the rust on the drive shaft? a lot of times its so bad the yokes and the the shaft cannot stay balanced ...

 

Can you send me a link for the "4wd high" you are referring to?

A slip-yoke is more expensive than I want to do now, I'm looking for cheaper options for now.

Yes it's an auto, is the 3.55 the best gears for a lift/ tire combo like I have?

 

Depending on your transfer case it will be 4H or 4 full time. "Best" for what? Power or MPG, or closest to stock ratio?
The cheap bandaid for a SYE is a TC drop. And check this chart for gear references. If you think a SYE is expensive, gears may be way out of your league.

 

You can't drive it in 4 full time without the rear driveshaft you need it in 4 part time.

 

8" of lift with a TC drop kit and only a driveshaft balance, I would have loved to see some photos of that.


To the OP a TC drop does not work as well with the 00-01's because of the LPD30 in the front compared to the HPD30 in the 99's and back. It increases the driveshaft angle on the front axle while helping the rear differential.


Before you re-gear make sure the tire size your running now are the largest you plan on running in the future, if you plan on going to a 33" tire that would need a 4.56 gear. A set of gears for both front and rear with install kits will run you just under $500 for both in parts. Also this is the time to install lockers if you can as no extra labor required.

 

8 inch on 37s no SYE , and no vibes, at all. even at 80mph +
it baffled me too lol
best one i could get of it

 

I agree with most of what FRED is saying, with the exception of lowering the transfercase, I think that lowering the transfercase will help.

I don't think your vibration is the "Rear Axle needing rebuilding", it is probably a U-joint, which is what Metmknice I think was leading too. If you have a bad rear Ujoint it will cause a vibration (I doubt your driveshaft needs re-balancing)

In short, your real question should be - "Does anybody know where there is a good shop in the town you live in" a good mechanic will find your problem.

If you just want to throw parts at it, I would change the rear driveshaft ujoints, my daughters 2000 with 3.5" lift would go through a set about once a year.

But it could be anything, driveshaft angle, ujoints, wheel joints, tire balance, bent axle shaft, bad hub, etc.

 

xjmachine sweet setup!

 

Must be a 2 door thing. Lol. Mine has 6 1/2 inch of lift with the stock driveshafts & barely has any vibration even at 80 mph. I couldn't believe it either.

 

thanks bud
gotta love them 2 doors lol

 

PS: With a 2000 your Front Dana 30LP is a Low Pinion, I would find a $100-150 Dana 30HP High Pinion, you will have better driveshaft angle as well as it is 20-30% stronger.