[Guest]

98 XJ 4.0 5-speed 4-door stock, new-to-me in late '00.
Has a nice Class II trailer hitch. Some weeks later I
noticed it was a little lower in the hind-quarters than
other XJ's (previous owner towin' some big honker boat?).
Rear leaves had some deformation near the eyes, so I
replaced them with new stock MOPAR's, which brought it
up some - later noticed it was still seemed a mite low
compared to similar XJ's (I'm running MICH LTX 225/75's
all around). Plan to begin towing a sailboat soon, and
I noticed that D*****r offers a 1-3/4" add-a-leaf lift
kit, which sounded just about right.

I talked with the folks at D*****r about other
bits'n'pieces that I might need, brake line ext's,
steering mods, T-case drop kit, etc, they said nope,
all you'll need is the 2 leaves and the (included)
thru-bolts (which turned out to be the wrong size) ...

As it turns out, it adds about 3" to 3-1/2" at the axle,
and about 4" at the trailer hitch, which was way more
than I wanted (Planned to add 3/4" pucks to the front,
but haven't done that yet). Immediately after installing
the leaf kit, I'm getting low-freq vibes in 4th gear
between about 40 and about 55 MPH, and then a medium
freq "brrrrr" at 60 MPH that stops when I put my hand
on the range shift lever (2H-4H-4L).

I've read recent entries and responses from Dark93
(01/11), blackdog (01/05), and rapax 1 (12/30) ...
thanks, guys ... and I guess it's time to check out
the U-joints, followed by the motor mounts and the
tranny mount (thanks JS for your description of a
U-joint inspection).

The XJ has 219K on the odo now, and it's been running
great up to now (lots of windshield time on the
thru-way). Front shocks are orig, rear shocks were
new 80-90K ago, U-joints are original.

Any comments / advice / suggestions to add to the
above ? This is a great forum ...

 

[krabysniper]

You seem inteligent enough to understand some of this so here are some links
Drive line angles

Drive line angles and phasing problems

Watson's guide to happy pinion angles

Have fun, and I hope you get it figured out.

 

[1572]

get some good steel shims , carry around alot of wieght and go out and flex it up during a day of wheelin. repeat as necesary until youre at the desired height/softness.

 

[3946]

My guess is that your u-joints are at an excessive angle. See kraby's post.

 

[2586]

A 1" transfer case drop might help at that hight, and it is fairly inexpensive. My 98 didn't start with vibes 'till I went from 3.5 to 4.5in, but I already had the T-case drop. Another option is take out out some of the leaves in the pack to get the desired hight (mix and match untill you are happy with the end result).

 

[Guest]

I'm going with Butcher on this one... while a trans case drop might help, both Tom Woods and Rubicon Express state that when lifting the newer xjs that much a double cardan shaft and SYE is required. Rear Pinion angles are then corrected using shims at the rear leaves. Neither of them rec'd dropping the transfer case to correct driveline vibes associated with lift-even though RE supplied 2 different t-case drop kits with my lift (go figure...). Although they did not offer a rationale as to why they prefer shims to the t-case drop I suspect it is due to changes in front shaft angles a t-case drop would cause. Think of it as a see-saw and remember the much shorter front shaft is gonna be a whole lot more sensitive to change than the longer rear shaft.
At nearly 4 inches of lift to the rear, his vibe could be coming from the over extended slip yoke more than anything else. After installation of my lift but before I tackled the SYE, I found I had (alot) less than 1 inch of the t-case output shaft engaging the driveshaft.
In any case both the drop and the shims are about the same price. Tom Woods has steel shims up to 6 degrees for $25. A t-case drop kit is about the same price give or take a buck and both are easily installed in the driveway with a decent floor jack, jack stands and hand tools.

 

[krabysniper]

My transfer case drop cost me 2 1/2 times less than that, less than $10 with brand new stainless steel hardware. really don't see how you figure messing with shims in back, which requires unbolting the u-bolts and relapecing the stud that holds the leafs together with a longer one, then putting it all back together, is easier than pulling the transmount bolts and letting it drop down an inch and slipping the new bolts and washers in place. 15mins compared to a minimum of 1 to 1 1/2 hours labor, hmmmm, I know which way I went