Drive line Vibration After Lift

Hello,

I'm sure this isn't a new topic, but I cant seem to find a solution to my drive line vib woes. I currently get vibes starting at about 60+ mph and it's important to note that I drive quite a bit on the hwy, esp with inter coming. I have a 3.5" OME lift, that turned out to be closer to 4". I have full leaf packs in the rear with 4 degree shims, Double Cardan drive shafts all around, a rusty's 1 inch t-case drop bracket, and stock control arms.

After measuring, the front pinion is angled 3-4 degrees below the center-line of the drive shaft....seems like a lot to me. I assume I would have to get adjustable control arms to fix this, unless I added more t-case drop in addition to the Rusty's 1 inch lowering cross-member. Is the t-case shift linkage the limiting factor on dropping it more? I've been messing with the rear pinion angle and have shims that are a little too big. I'll take them out and try to get the angle 1-2 degrees below the center line of the drive shaft when at rest.

Also, the front and rear shafts slope downward at 11.5 degrees and 12.5 degrees, respectively.

If anyone has experience with this, I would greatly appreciate some ideas. Thanks

Do you have a SYE kit on your tcase output ? Should if you have double cardan shafts

If so, the drop is isn't needed, and it compounding your front driveshaft issue. Tcase drops help rear shaft angle, but make the front one worse cuz it only drops the rear of the tcase.

Why do you think the front is causing the vibes ? Are you driving around with the front driveline engaged ?

In later models (or basically models with non-disco housings), even though the front output is not engaged the drive shaft spins.
Specs of your heep will help possibly narrow down issues as well.
SO, Year, engine, trans, t-case, axles, gears
Steps to confirm/fix your issues.
First, like said above, if you have SYE, then remove the lowering kit.
Then..
Pull front drive shaft, drive under symptom conditions, confirm fix or not.
Re-install front shaft. Pull rear shaft, and same as above.
IF either drive shaft is issue, get them balanced, repaired and/or replaced if necessary.
Have your tires road force balanced and rotated.
Check U-joints and the like as well, including in your front axle.
Check Unit bearings for play/binding, etc.

And, since you are running stock CA's check bushings.

TRCM said:

Do you have a SYE kit on your tcase output ? Should if you have double cardan shafts

If so, the drop is isn't needed, and it compounding your front driveshaft issue. Tcase drops help rear shaft angle, but make the front one worse cuz it only drops the rear of the tcase.

Why do you think the front is causing the vibes ? Are you driving around with the front driveline engaged ?

Click to expand...

I did install a SYE from advance adapters.

It should drop both, but not quite evenly. I only suggest the drop because the pinion angle in the front is 4 below the center of the shaft, similar to the rear angles when I was on my old axle shims. Figured it was a potential solution to fix both angles, or at least help in conjunction with other fixes

Not sure if the front angle is an issue. It does make more noise after the lift when I shift the t-case in to 4wd....

Johnnie Walker said:

In later models (or basically models with non-disco housings), even though the front output is not engaged the drive shaft spins.
Specs of your heep will help possibly narrow down issues as well.
SO, Year, engine, trans, t-case, axles, gears
Steps to confirm/fix your issues.
First, like said above, if you have SYE, then remove the lowering kit.
Then..
Pull front drive shaft, drive under symptom conditions, confirm fix or not.
Re-install front shaft. Pull rear shaft, and same as above.
IF either drive shaft is issue, get them balanced, repaired and/or replaced if necessary.
Have your tires road force balanced and rotated.
Check U-joints and the like as well, including in your front axle.
Check Unit bearings for play/binding, etc.

And, since you are running stock CA's check bushings.

Click to expand...

Specs:
2000, 4.0, AW4, Np231, D30 (4.10/truetrac), Chrysler 8.25 (4.11/truetrac)

Unfortunately, the lowering kit is my cross-member.....the factory one is long gone. I did fab up some 1/4" plates to raise the t-case 3/4" to return it close to the stock position, which made things worse, so I removed them.

I have yet to remove the front shaft....that's next on the list.

The u-joints look good (these shafts are only 1 year old and it did this when they were brand new). The tires are freshly balanced and there isn't play or binding in any bearings. I should have mentioned that I replaced the CA's with oem replacements, so those are good

If you cannot afford a full set of adjustable CA's, at the very least pick up a set of adjustable uppers, and some WJ or other better than stock fixed lowers.

Did you get a proper alignment done? If so, they set caster as it should, which will affect pinion angle. On lifted jeep, unless you turn the inner-C's for proper pinion angle, it will suffer at stock spec caster.
Could very well be a T-case/something in the t-case issue.

Johnnie Walker said:

If you cannot afford a full set of adjustable CA's, at the very least pick up a set of adjustable uppers, and some WJ or other better than stock fixed lowers.

Did you get a proper alignment done? If so, they set caster as it should, which will affect pinion angle. On lifted jeep, unless you turn the inner-C's for proper pinion angle, it will suffer at stock spec caster.
Could very well be a T-case/something in the t-case issue.

Click to expand...

I can do adjustable CA's, but only if it is justifiable....I'm not super familiar with when it is appropriate to put them into place

I've had two alignments within the last 1.5 years with no uneven tire wear or tracking. They talked about caster being out, but said they couldn't do much about it unless I had adjustable ball joints (or I'm assuming adjustable control arms would also solve this?)

The weird thing about the t-case was that it never made noise until after the lift/sye install...It may not be the t-case, but the noise is between there and the front axle.

If control arms are they way to go, is it worth my time/money to do a full set, or just the uppers? What brands have you guys had good luck with that aren't big $$$?

Adjustable Ball joints would adjust camber.
Even a single pair of adjustable control arms (Upper or lower), makes it easier to correct caster and pinion angle. A full set of adjustables, potentially give you the ability to center your tire or adjust wheelbase AND caster/pinion angle. The stock CA's are weak POS.

I recommend RK CA's. RK technically doesn't make them for XJ's anymore, but TJ front CA's are the same. The vendor Extreme Terrain over on jeepforum got me a good deal on RK arms.

As far as tires.. Out of balance tires can cause vibes and even make other issues more pronounced than they are.

Shows how much I deal with alignments....I leave that garbage to the people who deal with it everyday.

Ok, I'll have to look into those this week. As far as the rear situation, I'll put my original axle shims back in and go from there....followed by removing my front drive shaft for a test drive.

Not sure what the spec is supposed to be for CV type shafts as far as pinion angle. Pretty it's somewhere within a "couple/few degrees" below, if not right-on. Since the CV has the "angle"

Johnnie Walker said:

Not sure what the spec is supposed to be for CV type shafts as far as pinion angle. Pretty it's somewhere within a "couple/few degrees" below, if not right-on. Since the CV has the "angle"

Click to expand...

From what I've read, that's correct. It seems like people are shooting for 1-2 degrees below, so that's what I'm after I suppose.

Also, I contacted that vendor on Jeepforum, so we'll see what happens there

To reset castor, you only need adjustable lowers in the front until you get a lot of lift. Any benefit from new uppers would be strength or flex. I believe the adjustment is 5/16" of an inch for 3" of lift. Not a lot. I believe the factory sets the pinion two degrees below. That's why my stock 2001 Cherokee measured with stock & level ride height.

md21722 said:

To reset castor, you only need adjustable lowers in the front until you get a lot of lift. Any benefit from new uppers would be strength or flex. I believe the adjustment is 5/16" of an inch for 3" of lift. Not a lot. I believe the factory sets the pinion two degrees below. That's why my stock 2001 Cherokee measured with stock & level ride height.

Click to expand...

I'm just trying to wrap my mind around this....To rotate the pinion up, I would have to shorten the lower CA's....Is that going to pull the axle toward the rear of the jeep more, without having adjustable upper CA's?

md21722 said:

To reset castor, you only need adjustable lowers in the front until you get a lot of lift. Any benefit from new uppers would be strength or flex. I believe the adjustment is 5/16" of an inch for 3" of lift. Not a lot. I believe the factory sets the pinion two degrees below. That's why my stock 2001 Cherokee measured with stock & level ride height.

Click to expand...

escout said:

I'm just trying to wrap my mind around this....To rotate the pinion up, I would have to shorten the lower CA's....Is that going to pull the axle toward the rear of the jeep more, without having adjustable upper CA's?

Click to expand...

Actually a set of either UCA or LCA will enable you to set caster. But most adj. LCA do not go much shorter than stock if at all. But, this pulls your axle back more, which is not good.
But, since you have stock CA's it makes sense to upgrade to full adjustable.
Not only will you get better articulation with aftermarket CA's, but overall adjustability is simpler.

When you raise the front end you're supposed to need to lengthen the lower LCA.

Lift Height LCA UCA
Stock 15.75" 15"
2" 16" 15"
3" 16" 15"
4" 16.33" 15"
4.5" 16.5" 15"
5" 16.6" 15.25"

This data is from a chart that can be searched for. I don't have a link.

escout said:

I did install a SYE from advance adapters.

It should drop both, but not quite evenly. I only suggest the drop because the pinion angle in the front is 4 below the center of the shaft, similar to the rear angles when I was on my old axle shims. Figured it was a potential solution to fix both angles, or at least help in conjunction with other fixes

Not sure if the front angle is an issue. It does make more noise after the lift when I shift the t-case in to 4wd....

Click to expand...

The tcase drop does drop both outputs...true....BUT....since the trans/tcase are connected to the motor, and the motor didn't get dropped, the tcase now rotates with the motor mounts being the pivot.

What this does, is it lowers the tcase rear output lets say 1", and in doing that, the vertical angle on the output goes from 90 deg, or straight up, to 89 deg, or slightly angled down. The front output may lowered 3/4", and it's angle goes from 90 deg, or straight up, to the same 89 deg, but in this case it angles it UP more, not down.

The problem is that on the rear driveshaft, this slight down angle HELPS with driveline angles.....because the change in the output actually aligns it with the rear pinion.

This same angle tho, in a front output, moves it's alignment away from the front pinion because it rotates up, not down. This doesn't really affect the u-joint angle at the pinion, but it DOES affect the u-joint angle at the front output.


Kinda like if you park your jeep centered in a spot, you have equal clearance for the doors to open on both sides, but if you park crooked, then the doors on 1 side have more room to open and the doors on the other side have less.

Hello,
Old thread, I know....But I figured I should at least wrap this one up, since i spaced it for a couple years, ha.

Recap:
After I installed the lift and extras on my XJ, I was having driveline vibes, generally around 70mph and/or under hard acceleration. They weren't awful, but enough to annoy me as a daily driver. The lift kit that I purchased came with a double cardon rear shaft, SYE, and shims to correct the pinion angle.

The problem with the shims in the kit, was they did not give me the angles I was looking for, nor did any other set of shims I ordered (I tried three different sets). Being that it's a double cardan shaft, (in a perfect world) you want to see 0 degrees of difference between the pinion angle and slope of the shaft, but to account for pinion rise under load, that pinion needs to be set about 1-2 degrees lower than the shaft going onto it.

So basically, the only effective way for me to attain those angles was to cut off the stock spring perches, and re-weld a new set on. The axle and suspension had to be jacked up together to their resting (parked) state, and at the same time, the axle rotated to achieve the desired pinion angles....then the perches welded back on. Kind of a PITA, but it's the only way to go to really dial in those angles. Driveshafts can be very sensitive to the angle changes that come with lift kits and so forth. Anyways, shims have worked out for me in the past, and are generally a decent option, but didn't cut the mustard the time around.