XJ drive-line vibration issue

[b52]

Hello everyone,

I'm damn near sick of this drive line vibration i have in the rear of my 2000 Jeep Cherokee and I have gone far and beyond to address the issue which has only slightly cured it.

My Jeep is a 2000 Cherokee 4 door, 4.0L, 4X4 NP231 t-case and AWD 4 auto tranny and it has the Chrysler 8.25 rear end. It has a 3.5 inch RE super flex lift kit (with full leaf packs) and I'm running 31x10.5 A/T tires and the truck has 153,000 km's on the OD.

I have done the following modifications to remedy the problem; I installed an advanced adapters slip-yoke eliminator kit and laced it to a Tom woods CV drive shaft. After the install of the slip yoke and cv drive shaft the vibrations were significantly reduced, however was still very noticeable. I then installed rear axle shims (can't remember the angle measurement) to bring the pinion angle closer to stock and dropped the t-case, however, I still have the drive line vibrations in and around 90 to 120 KM/H. I just recently took the Jeep in to a drive line specialist and they inspected every thing and decided that the tom woods drive shaft needed to be balanced claiming that the balance was "all out of wack" and even after completing that it still vibrates.

The worst part of it all is that I'm changing the rear u-joint that connects the drive shaft to the rear axle every 2-3000 km's, this is not normal. Please if anyone has any insight as to what else I can do or what I should look into, please, let me know. Has anyone else experienced this?

Thanks in advance,

- Thane

 

[Backwoods Rambler]

That's weird, I've never heard of an XJ having driveline vibes :elkgrin: :elkgrin:

 

[b52]

Well, is it normal to be replacing u-joints every 2-3000 KM's?

 

[alosix]

The worst part of it all is that I'm changing the rear u-joint that connects the drive shaft to the rear axle every 2-3000 km's, this is not normal. Please if anyone has any insight as to what else I can do or what I should look into, please, let me know. Has anyone else experienced this?

I think I'd start looking here.

Is there anything wrong with the yoke?

Does the yoke/pinion move (up/down/sideways) at all? (thinking worn bearing)

Possibly using a slightly undersized ujoint?

Not seeing any binding @ the joint right?

 

[b52]

I think I'd start looking here.

Is there anything wrong with the yoke?

Does the yoke/pinion move (up/down/sideways) at all? (thinking worn bearing)

Possibly using a slightly undersized ujoint?

Not seeing any binding @ the joint right?

Im not to sure about the yoke/pinion moving, well it could be that. I have noticed that I do get slight "jerks" when at a dead stop and accelerating (but not hard acceleration) it feels as if though the drive shaft is almost skipping or that there is play at the joint.

How would I be able to tell if there is any binding at the joint? I mean, it's clearly on an angle, but there isn't any contact or anything like that but the angle is alot bigger than it was when it was stock (it is lifted after all).

The u-joint is of the right size. When I ordered the drive shaft it came with the gold seal u-joints and I have replaced that specific u-joint many times and the last few times my mechanic did it, so I'm sure we could rule it out.

I don't think there is anything with the yoke as my mechanic can't find anything wrong with it. The jeep only has 153,000 km's and has barely been off-road. How long does the yoke typically last?

 

[alosix]

There really shouldn't be much angle at all @ the DS joint when you are running a CV. What degree shims did you install?

Jason

 

[BEVAN]

There really shouldn't be much angle at all @ the DS joint when you are running a CV. What degree shims did you install?

Jason

I was thinking the same thing, could be to much deg with the t-case drop.

 

[Root Moose]

There really shouldn't be much angle at all @ the DS joint when you are running a CV. What degree shims did you install?

Jason

I was thinking the same thing, could be to much deg with the t-case drop.

Agree. You should be able to draw a straight line through the prop shaft centre line through the centre line of the pinion. Well, a degree or two to take up torque rotation and keep the u-joint lubed under power is ok.

With a CV shaft the angle of the pinion should NOT be anywhere near stock in an XJ. Pull that transfer case drop too. One of the reasons to run a CV shaft is to not have to run a kludge like a transfer case drop.

HTH

 

[BEVAN]

Make sure your front trac bar bolt on the axle is verrrry tight...that plagued me for 4 months...

 

[x Magoo x]

I had bad vibrations on my XJ around 50-60 mph and found it was due to cupped front tires. I never rotated my tires and it cupped the front tires. I moved the front tires to the back and it is less noticeable and hopefully disappear with wear over the next few thousand miles.

 

[wADVr]

It is not uncommon for a mail order DL to be out of balance. (not to call any one brand out...) If thats covered now and the shop has inspected the CV joint including the center ball move to making sure the angles are correct as said above. Shim the axle to have the pinion 1-2 degrees flatter than the DL.
Then I would move to the front DL and have it inspected/balanced/serviced. Simply remove it and take it for a test drive. Check your angles there too as more than likely you will have to sacrafice a degree or two of caster to raise the pinion to better match the DL angle, especially with the low pinion axle you more than likely have in the front of your XJ. The front does not explain the rear Dl going through u joints but will help with the vibes and is commonly overlooked.

 

[madizell]

Root Moose has it exactly right. The T-case drop was part of the kit to keep stock driveline and joints within stock limits. With the slip eliminator and CV shaft, you are way beyond stock. The T-case drop has to go.

Also, the CV does all the joint alignment duty here. Because it is a double cardon joint, it is not only not necessary to keep all joints in phase, but counter productive. The rear joint angle should, as mentioned, be close to zero (actually by setting the pinion joint to zero you will be "in phase" with the second of the two cardon joints, the one nearest the rear -- anything else is technically out of phase). There is sufficient movement pf the pinion end joint due to suspension loading and accel/decel to move the rear joint around, so it will stay lubed, although you will want to keep the lube fresh anyway. If your shaft is built with a lifetime lube joint (no zerk) consider swapping it out for an HD unit that can be lubed.

In order to achieve zero angle at the pinion it may be necessary to cut and relocate spring perches.

The low power slow acceleration jumping you sometimes feel is most likely joint binding. You are probably running the joint at or very close to maximum degree of deflection. Running a joint like that for long will destroy it, which would account for you going through joints every 2K. No matter how you drive, running a joint at max deflection will beat the crap out of it in short order.

Drive shaft balance is not usually an issue unless you tend to drive at highway speeds all the time. Cardon joints are massive and have a bit of free play in them anyway, so perfect balance is not only difficult to achieve but not as important. If you get everything else right, a bit of out-of-balance won't even be noticed.

 

[b52]

First off, you guys are awesome. Thanks for all of the input but I've got some more info and updates for you.

When I took the Jeep in to the drive line specialists he said to me that the angle was already far greater than it should be and suggested that the only remedy would be to lower the Jeep a little, which I know is B.S considering that I have done all of these conversions to accommodate the lift (which isn't a big lift at all). The specialist got under the jeep and took measurements of the pinion angle and then punched the numbers into a computer software program and came up with the pinion angle number (i think that's what the number was called) which If i remember was somewhere in and around 800 (if this makes sense to anyone, god bless you). After figuring all of that out the only thing they could offer me was to balance the drive shaft and suggested I lower the truck slightly and or to put a larger degree shim on the real axle as opposed to the ones I already have in there. OH! I forgot to mention that I removed the t-case lowering kit yesterday and wouldn't you know it, same ********, nothing has really changed. Today I loaded the trunk up with approximately 440 lbs worth of packaged salt (don't ask) to level the truck out because my front springs have settled due to the front bumper and the rear springs are unbelievably stiff and the truck sits alot higher in the back then the front. Even after that it hasn't really changed much, my Jeep just drives like it's been on a McDonald's diet for the last 5 months :elkgrin:

Keep your input coming, I really do appreciate it!

 

[Root Moose]

"drive line specialist"

Ain't that a joke...

Point your differential input at the output of the transfer minus 1 degree and you will be golden.

Theory why:

U-joints vibrate when running at an angle.

In order to have a smooth running drive line u-joints are paired together and phased such that their combined vibrations cancel out.

This is what happens at the transfer case end of your new propellor shaft. The two u-joints at that end cancel out each others vibrations.

The differential end of the propellor shaft has only one u-joint. If it runs at an angle you will feel the vibration caused by the joint. The greater the angle the more the vibration.

You are in Toronto. Take your Jeep to National 4x4 in Burlington and get this fixed properly if you are not able to deal with it yourself.

HTH

 

[madizell]

Well, not being familiar with your "specialist's" computer program, it would be hard to comment on what he was trying to accomplish, but let me guess, the program is intended to deal with stock drive lines, not custom creations. If you had a stock drive shaft, you would have two u-joints, one at the T-case, one at the pinion. These joints would have to be kept close to the same angle to keep the joints running in the same ellipse at the same speed. A computer program could do something like this fairly easily because it is just math. Each joint in a standard drive shaft should be at an equal but opposite angle from its mate.

The double cardon joint creates a zero angle at the output end of the joint, regardless of the angle at which the shaft lies at rest. Some folks refer to these as constant velocity joints. Because the double cardon leaves the drive shaft without any joint to joint speed matching issues, putting an angle on the pinion end joint defeats the purpose of having the double cardon by creating a drive shaft with ONE joint running without another to balance out rotational variations arising from the design of the joint. The farther the pinion end joint is from zero the worse the vibrations, so when your specialist cranked in additional pinion angle, he made matters worse, not better, assuming that when he added shims he pointed the nose of the pinion down instead of up.

The pinion shaft needs to point straight at the output end of the double cardon joint. This almost certainly will require pointing the pinion UP from where it was when stock. Most shims cause the pinion to point DOWN when installed as intended. If this is what was done with your vehicle, you may be able to mitigate the misalignment by installing the shims the other way around, but best to get under your ride and take a look to see which way the shims are installed, and how much of an angle the rear joint is running at. Check for running angle with the car normally loaded and the tires on the ground, not hanging in space, which should put the drive line somewhere in the middle of its range of travel.

You can lift a vehicle to such an extent that joints run at 20 to 40 degrees without creating dangerous vibration if you use the right joints. With your small degree of lift, you should be not more than 10 to 20 degrees at the double cardon, which should be within the range of a standard joint (I believe a standard double cardon will run at around 30 degrees without binding), and near zero at the rear, which obviously is within range of any u-joint. If your guy set up the pinion so that it too had 15 degrees of tilt between pinion shaft and drive shaft, it is already close to its working limit, and could bind, depending on the exact joint used. There are high-clearance, high angle joints out there, but most folks don't use them. Or to put it the other way around, those who do use them also know how to build a proper drive shaft.

Anyway, the safest and easiest way to realign your pinion will be to reset the spring perches, which requires taking the axle loose from the springs, cutting off the old perches, and welding on new ones after grinding off the weld lines. Shims are okay for verifying new running angles, but I really don't think they are a best option for long term use because they can and do wear, they can shift around, and they can pop out under stress, which can lead to parts failure in bad places when the u-bolts go loose from loosing a shim.

Thousands of Cherokees have been successfully lifted with no drive line issues, so have faith that this can be worked out, probably for the price of a pair of perches, obtainable from truck and trailer supply houses, and a few hours of time and effort with torch, grinder, and welder. If you don't have these tools, find someone who does. Lots of time, these changes can be done for the price of a case of brew, and a few hours with a couple of buddies.

If you have access to a digital camera and can post a few shots, why not post some photos for us to see, and perhaps it help to illustrate the problem.