Kevin108

A lot of what I've read has said that when you do this lift, you need to replace the u-joints as the needle bearings have worn in at the previous driveshaft and can cause vibrations. That's a cheap and easy place to start.

brutalxj

Or just throw on some swapers. Lol

RENIXBEAST

^^^^I'm guessing he's saying swampers???^^^^^^

RENIXBEAST

I run a SYE and a 1" tc drop and have no vibes. I'm wondering if I should remove the tc drop??? Or will this cause vibes???

NH_Jeep_XJ

Since this is under the category of Cherokee Tech.

Has anyone thought of measuring their before and after pinion angles ?

I know from years ago when I used to hang around sports car club racers, the way in which they achieved better HP ,speed and lap times was by minimizing the drag on their Driveline and U Joints by working with their pinion angles.

Also, it was well known that excessive pinion angles and driveline geometry were the real culprit behind broken driveshafts, tailshafts and cracked bellhousings.

So in looking at this in the perspective OF an Alignment issue.
What if one were to measure the driveline angles before the Lift, when we had no vibrations.

And then measured after the Lift has been installed when we did ?

This way you would at least understand in degrees how far you are off as well as possibly why TCase drops and shims might work and sometimes don't.

One thing we might considering referencing are the actual factory driveline specs. I am certain that they are specified to operate vibration free within a range/number of degrees.

NH_Jeep_XJ

I think that Kevin108's suggestion to replace/inspect the U Joints before lifting makes a lot of sense.

As most of these XJ's are being purchased used and have 100k or so on the clock, I am not at all surprised that many are encountering vibrations after lifting and placing more stress on an already tired and worn drivetrain.

From what I understand the 2000 and later are more prone to vibs due to added caster as a result Jeep switching to a low pinion D30 from the High pinion used 85-99.

The low pinions have a greater difference between the diff angle and the true caster due to the diff uni needing to point up higher towards the transfercase.

I too wanna do a 3" Lift on my 98 very soon but the more I am thinking about it. I am going to check my driveline for U Joint wear and slop first.

Like the old sayin' "Lipstick on a Pig ..." .

BigC9164

i just did a 3in rough country lift with full packs(the full packs are 3.5in) on my 1999 with a manual trans (ax-15) and i get bad vibes. so i am thinking about getting some 3/4 coil spacers up front to lessen the drive shaft angle. i have a TC drop sitting around and am hesitant to put in on because people say it destroys motor mounts. Can anyone give me some incite as to what i should do. i already have the tc drop and don't care about loosing the ground clearance because i live in florida and dont haave any hills or rocks to climb. please tell me if the tc drop will REALLY break my motor mounts in a year or two. THANKS!

Crunch

I put all new u joints in at the time I installed my lift, front and rear shafts... I also swapped my front axle to a hp30 at that time also.... Still have the vibes even with a t-case drop...

Crunch

I put a .5" spacer on my front springs to.... I know a bunch of guys that are running t-case drops without issue.. Not my first choice but way cheaper.. At least to limp with till can afford a sye...

DualSportDad

I just put my t case drop on. The other day. Driving around town the jeep was smooth but on the highway it was buzzy. So far so good.

I did measure the angles.14 deg before and 12 deg after. This is a 97 with a 3" lift. I think what really helped it that the t case drop really brought the drive shaft back up on the t case output shaft.

NH_Jeep_XJ

Here's the source of that information pertaining to the vibes and their relationship to pinion/driveline angles. Apparently the 00-02 were shipped with added caster adding to the narrowing of the window necessary to attain a vibe free drivetrain.
Your caster should decrease as you lift the drivetrain. The fact that the 2000 and greater came with added caster points to their inherent problems with vibes.

High Pinion D30 used 85-99
Low Pinion D30 used 00-02

"This table to compares diff degrees to true caster for a high pinion D30 as used of XJ's 85-99 and low pinion as used in 00-02. The low pinions have a great difference between the diff angle and the true caster due to the diff uni needing to point up higher towards the transfercase. They also run an extra 1/2 degree of caster to start with. In brackets is the recommended caster for different lift heights. The reason recommended caster reduces as the lift height increases, is the uni angles get too steep as the lift increase so can introduce vibes. Always run as much caster as you can without vibes but below is a guide I have found works for most. Diff degrees shows two sets of figures depending if reading off the vertical or horizontal. Top of diff should be tilting forwards. The more it tilts the less caster you have.



I tried to just text format the table in but it's coming out jumbled.
Check the link...till I can upload the image.


Diff Degrees Hi Pinion Low Pinion
87.5 or 2.5 6.5 ( 0-2" ) 9.5
87.0 or 3.0 6.0 ( 3" lift ) 9.0
86.5 or 3.5 5.5 ( 4" lift ) 8.5
86.0 or 4.0 5.0 ( 5" lift ) 8.0
85.5 or 4.5 4.5 ( 6" lift ) 7.5
85.0 or 5.0 4.0 7.0 ( 0"-2" )
84.5 or 5.5 3.5 6.5 ( 3" lift )
84.0 or 6.0 3.0 6.0 ( 4" lift )
83.5 or 6.5 2.5 5.5 ( 5" lift )
83.0 or 7.0 2.0 5.0
82.5 or 7.5 1.5 4.5
82.0 or 8.0 1.0 4
81.5 or 8.5 0.5 3.5
81 or 9.0 0.0 3.0


Let's look at the data and get a explanation as to why we have vibes or not.
We need to measure our angles in the same manner for consistency of our data.

Read the article to understand how he is measuring his angles so we can all understand and present our data. Also to get a clearer view of the table.

We will figure this vibe issue out.




http://www.go.jeep-xj.info/HowtoAlignment.htm

Infidel_XJ

Why are so many of these discussions the same? It always turns into...my 300 friends didnt get vibes....and my 500 friends did.... Point is...if he has vibes...he has vibes. Go with the IRO kit for $200.....good setup...good price....should solve your problems.
I'm a big believer in doing things right the first time with good parts...and correct parts. Can't afford em...save up... I'm running into this problem with my SBRs too. I started building them for some friends who spend over $2k on a rifle...$400 on tax stamps for a can and to SBR it...and wanna shoot cheap Russian ammo for it.
My 96 had no vibes til I went over 4"...my 97 has vibes when I hit 3"....it happens.....
Sorry to vent...it's midnight over here and sometimes this just gets old...aaarrrggghhhhh

mikeXJ1020

Just for the record i have a 3.5" lift, 1" tcase drop, Auto, Np242, C8.25 rear and the vibes on the highway especially at 65 mph were so unbareable that i would get the worst headaches.

Swapped in a Np231 with Sye. All better

-Mike

NH_Jeep_XJ

Granted we all know that by buying something over the counter or by purchasing the SYE one can readily resolve the vibration issue.

But since this is a TECHNICAL discussion, The bigger question is Why are these vibrations Occurring on a meager 3" Lift in the first place ?

It has much to do with proper alignment.

One of the first things they say one should do after lifting is to get the Alignment checked. Remember Read THE Friggin Manual ?

There is a REASON for this.

The LIFT changes your alignment and suspension geometry which is the root cause of the problem.

It's not the type of lift you install, your luck, phase of the moon or your astrological sign.

The table on the alignment page points out this information as well as the acceptable Caster parameters based upon lift height and TCase type.

For a 3" Lift it says:

Caster @ 6* Degrees with Hi Pinion - 85-99 XJ D30
Caster @ 9* Degrees with Low Pinion - 00-02 XJ D30


Get your alignment done at a reputable alignment shop.

And Not at one of these Red Green Light bubble alignment shops manned by Noobs.

And see how out of spec you are before resorting to masking a problem with another band aid fix.

If the Alignment doesn't cure the problem only then would I look at a TCase drop and/or SYE.

There is big money to be made on peoples lack of technical knowledge in the automotive aftermarket.

Knowledge can be gained for free if you are only willing to learn and READ.

But a fool and his money are soon parted.



http://go.jeep-xj.info/HowtoAlignment.htm