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View Full Version : Death wobble and front diff - separate problems?


br1anstorm
September 27th, 2017, 07:17
I have a 1993 XJ 4.0 Sport auto, stock and unmodified. It has done some 150,000 miles, only a few of which have been seriously offroad. I have rarely needed to use 4WD. Can't recall offhand whether it has SelecTrac or CommandTrac 4WD (if that is relevant).

I'd welcome advice on a couple of problems which may or may not be related.



The problems (and symptoms). The Jeep is showing signs of developing a "death wobble" - again. It had this before, about 5 years ago, and after changing out various bushings etc, what eventually cured it then was replacing the upper and lower control arms and all their bushings on both sides. But that problem is reappearing. In addition, I noted a slight "grinding" noise from somewhere in the front end when turning hard on full-lock both left and right - as when going round a roundabout.
The evidence so far. I'm relying on the help of my local workshop mechanic, whose main work is looking after rally cars rather than fixing Jeeps - but he knows what he is doing. We have found that the 5-year old black rubber bushings in the control arms are shot. This may be enough to explain the re-emerging DW. We are pretty certain that there is nothing wrong with the universal joints at the front wheels: they were replaced a year ago, and the sound now audible on full lock is not the typical 'clicking' sound of worn UJs. But my mechanic friend has found what he reckons is excessive play in the front propshaft linking into the front diff. Could this cause the noise on full lock? He says it may be insufficient preloading (?). This takes the analysis beyond my pay-grade and skill-level!
The diagnosis. As noted, we think/hope that the worn bushings may be the cause of the DW. The question is, what to do about the propshaft/front diff? My mechanic has taken off the diff cover and had a look. In summary it seems there is no sign of serious damage or failure, but that the gear-teeth are not engaging fully or cleanly. I am assuming (I haven't had a chance to look) that this is where the propshaft engages with the gears inside the diff... The concern is that this may sooner or later result in the gears being chewed up, or something breaking inside the diff.
Solutions? We're going to replace the control arm bushings anyway as I have a set of spare/replacement red poly bushings. We'll see if that solves the DW. As for the diff, the suggestion is simply to remove the front propshaft... This obviously removes the 4WD option, which is a slight pity but no great loss as I rarely if ever need to use it.

But I'd welcome NAXJA experts' comments on the evidence and diagnosis so far, and any advice as to whether this is the best/simplest/only solution. If we do remove the front propshaft, are there any points to watch, or downsides, or precautions that we need to take to ensure that what's left in terms of the diff, front drive shafts, etc aren't at risk?

Green XJ Jeep
September 27th, 2017, 08:50
Look at your axleshaft u joints.

md21722
September 27th, 2017, 09:26
I would look at the u-joints. I have no idea what he is talking about with the front driveshaft and how it relates to the ring and pinion. It sounds like he doesn't know what he's talking about either. Or somebody isn't explaining it well. If the pinion bearings are worn the pinion can move in and out slightly. Typically this will lead to seal failure and you'll have a leak. You might be able to feel it if you grab onto the yoke and push and pull. There should be no movement. You could also mark the ring gear with gear marking compound and check the pattern. The most common front driveline related problems are bad wheel bearings, bad u-joints (can cause grinding, notchy steering, etc) , looseness in the slip joint of the front driveshaft (which can create a vibration at high speed), or roughness in the double cardan (causes "angry sparrows noise"). If the front control arm bushings are shot after only 5 years, I have to ask, were they tightened with the Jeep resting on all 4 wheels? Bushings should NEVER be tightened with the tires hanging in the air. That would mean the only time they are at rest is when its on the lift!

br1anstorm
September 27th, 2017, 11:14
Thanks - especially md21722 - for those thoughts. If the explanation isn't clear, it's probably because I didn't fully grasp what I was told....! My understanding was that there was some movement (back and forth?) of the pinion.... ie the part at the forward end of the front PROP shaft where it connects into the diff. But I may have misunderstood.

I can at least say that there was/is no obvious sign of leaks. Nor have I had any high-speed vibration. Not sure exactly what an angry sparrow sounds like, but I don't think that's the noise I was hearing: what I heard was more of a low-frequency grinding/groaning.

Part of the challenge is getting clarity about which specific parts (gear/pinion/u-joints/cardan etc) we are talking about. And the difference between drive shafts (of which there are two, one to each front wheel ); axle shafts (the same things?); and propshaft (between transfer case and front diff). Sometimes the tech terms differ on this side of the Atlantic! Just for example, there are u-joints at the outer end of each front drive shaft.... and u-joints also at each end of the front prop shaft. On my Jeep the former ones - which is what I think Green XJ Jeep means by the axleshaft u-joints - were replaced just 6 months ago, and checked to pass the annual roadworthiness test, for which they are a critical item. And they don't click on full lock, which is what those u-joints normally do when they are failing.

Can't be 100% certain on the separate question of whether the control arm bushings were tightened with wheels on or off the ground all those years ago - but thanks for the advice: I'll make sure that it's done right when the replacement poly ones are fitted.

Question remains: to remove the front propshaft completely or not?

md21722
September 27th, 2017, 12:03
In U.S. terminology, the shafts that go to the left and right wheel are called axle shafts and driveshaft/prop shaft connect from the center of the axle to the transfer case.

I was mentioning common complaints from the front end. When you're turning left or right and have noises I would suspect u-joints or the unit bearings. Don't rely on clicking to diagnose u-joints. They can binding or ready to fall out but make no noise.

lawsoncl
September 27th, 2017, 13:20
If you have the vacuum disconnect on the front axle, the front prop shaft isn't spinning much anyway. For me, bad u-joints at the wheels have always manifested as a vibration or grinding noise when turning. At that point thought, they're either obviously sloppy when you grab them and wiggle them or they feel very tight when you try to spin the wheel with it up on jackstands and the steering wheel cranks over.

For the wobble, check the obvious. Have someone turn the steering back and forth while you crawl under and feel all the rod-ends and look for anything moving that shouldn't be. Swap tires front-back too, just to make sure it's not tires. If the damper is leaking, replace it (yea, I know a damper is technically a bandaid for a poor design).

br1anstorm
September 27th, 2017, 13:22
[In reply to md21722] Two nations divided by a common language.......?

I'm heading down to the workshop tomorrow to take a look under the Jeep while it's up on the lift. With luck I might come back with a better idea of what's loose, what's tight, what's leaking, and what's making what kind of noise!

Watch this space.....

[in reply to lawsoncl] Vacuum disconnect? That's a new one on me. Maybe that's part of the subtle distinction between CommandTrac and SelecTrac 4WD? I had always thought that the 4WD/high/low shift lever on my XJ was essentially mechanical - but then I'm no engineer and I fear that again we're venturing above my skill level and pay grade (!). I also understood that when the drive to the front wheels was not engaged, the front wheels effectively turned the 'axle' shafts, which in turn rotated the front prop shaft freely - at whatever speed the wheels were turning. But the detail of how Jeep 4WD works is perhaps not critical to solving the current problem.

As for the incipient DW (and it's not yet frequent or severe), if replacing the control arm bushings with poly ones doesn't improve matters, I fear I'll have no option but to work my way through the familiar list of other possible troubleshooting steps that I remember from last time. I still have spare sets of tie rod ends, balljoints and a steering damper which we changed out fruitlessly during the last DW saga 5 years ago.

blondejoncherokee
September 27th, 2017, 14:15
have someone turn the wheel back and forth while you inspect the trackbar bushings/joints. My money is on bad trackbar joints.
Same for TREs, and control arms. make sure trackbar and control arm mounts are not wallowed out as well. jack up the rig and Check ball joints, also get your tires balanced.

JeepNoob
September 28th, 2017, 07:20
Normally, gears inside a diff with have a bit of slop between them. As the vehicle is driven, they will heat and expand, providing a better, less sloppy fit. If you're really that worried about, I would have your mechanic check the backlash on the gears and verify that it's within spec.

br1anstorm
September 28th, 2017, 10:56
Okay - latest update and clarification after workshop trip today.

The front diff issue is indeed a problem of sloppiness/movement of the pinion. There's virtually no sign of a leak, but the conclusion is that the bearings are worn - as earlier described by md21722:

......... If the pinion bearings are worn the pinion can move in and out slightly. Typically this will lead to seal failure and you'll have a leak. You might be able to feel it if you grab onto the yoke and push and pull. There should be no movement. You could also mark the ring gear with gear marking compound and check the pattern.........

So the front prop shaft has been disconnected and removed, and I've now got to source a bearing replacement kit or set of parts (assuming such is available from Rock Auto or elsewhere). The parts manual I have suggests that there are two 'bearing packages' (p/n J812 4052 and J812 6499) plus a baffle (p/n J093 4937).

I wonder whether I have to get a complete ring and pinion gear set as well (p/n varies depending on gear ratio, and I have no idea whether my 93 XJ has the 3.07, 3.55, 4.10 or 4.56 - how do I check?). And is the Dana 30 the only model of front diff fitted to a 93 XJ? I'm beginning to think this will all be so costly I'll have to settle for 2WD and do without the 4WD option permanently!

As for the separate problem of the death wobble, all the control arm bushings have been replaced with poly ones (and tightened with wheels on the ground). So far, touch wood, a trial run shows no DW.

There remains a slight noise on full left lock, which seems to be the front right CV joint, and the right shock absorber (I have Rancho 5000s) is a bit leaky and soft. I'm going to leave the task of replacing these for a few weeks or months.

Green XJ Jeep
September 28th, 2017, 11:15
If the gears arent damaged you can get ring and pinion install kit from RWK Haus Supply, or Just Differentials.

Have you replaced your track bar? It is another contributor to death wobble

md21722
September 28th, 2017, 11:21
I would only buy a new R&P if the gears show signs of wear. The axle may have a tag that indicates the gear ratio, the ring gear will be stamped with that information, or you can count it. I would not buy bearings from Jeep unless they are cheaper.

Spicer 706015X Inner Pinion Bearing Kit - includes bearing/race HM88649 HM88610
Spicer 706030X Outer Pinion Bearing Kit - includes bearing/race 02820 02872
Spicer 706938X Dana 30 Master Shim Kit
Spicer 32349 baffle
Spicer 44895 pinion seal

you can also buy a gear setup kit for the D30 from a gear supply house.

If your guy does not know how to setup gears look elsewhere. Its not just a matter of changing the bearings and calling it good. The mesh & preloads need to be set correctly.

br1anstorm
September 28th, 2017, 16:04
Thanks - especially for those Spicer part numbers. Very helpful in sourcing the parts over here....

I don't believe the gears themselves are significantly worn, so hope to avoid having to do the whole R&P thing. I think "my guy" will be able to replace and re-set the bearings if we can get the right parts. It's true that he's more accustomed to rebuilding and maintaining Subaru rally cars - some of which are 4WD, albeit a different system - but I reckon he'll be able to manage the preloading etc on a Jeep setup once we know the necessary settings and spec.