Vibration issue!!!!

[junglejuice]

I am not sure if this is in the right section...

Firstly I need to add that my Xj has the 4.0 litre I6 with the Aw4 auto which is stock for here in Australia, it is regeared to 3.73:1 running an Old Man Emu 2" lift kit with rear airbags.

This issue reared its ugly head when preparing for our recent trip to Tassie (3000kms each way) whereby it would vibrate at 100kmh~ I had recently added an extra leaf to my OME pack as well as fitted a secondhand set of wheels and tyres, stock sized 225/75/15's on alloys which I had balanced.
I fitted a 2.5* castor wedge (I am running a SYE) to the rear but all the way to Tassie and back it vibrated at anything over 99kmh and it is a long way.
I noticed on the first day that 3 of the 4 wheels lost their weights so once I got back I had them rebalanced and was told by the tyre mob that stock Jeep alloys require special weights which they now had so redid it for free.

No improvement...

So I removed the extra leaf, no improvement...
I had an issue with the transfer case which meant the removal of the SYE, no change.
Lowered the rear by removing the inverted leaf from my OME pack, down to 1.5", no change.
Tried a second stock tail shaft, no change.
Tried a set of stock steelies with good cond 235/75/15's all freshly balanced, no change.
Refitted my modified output shaft with the SYE to my replacement transfer case, no change.
Fitted some 6* caster wedges with the SYE sitting at 2.5", diff @ 78*, tailshaft @ 80*, no change.
Tried another front drive shaft in the rear with the SYE, no change.
What I noticed today is if I lift off the pedal all the vibes disappear, as soon as I ease back on the pedal they come back, I also tried dropping it back to 3rd to see if it might be the harmonic balancer which changed the revs from ~2k to ~3.5k, no change.

Has anybody got any suggestions as this is driving me insane?

Cheers, JJ

[cantab27]

front bearing going bad jj... had one do that when i hit 80k it would kinda vibrate..

[Mudderoy]

The front u-joint in my rear drive shaft would cause vibrations with throttle on and pretty much go away with throttle off. That was at about 55 mph.

You said you changed the drive shaft. Hmmm Did you try it without a drive shaft? It is possible to run with one or the other. Perhaps testing without a front, then without a rear drive shaft it would help you point to the problem.

[4.3LXJ]

Wos JJ, you have done a lot of things to this. So if I read this right, you now have an SYE in? If so, then you should be able to draw a straight line on the pinion shaft and drive shaft with no flex on the ujoint. It should look like this:

http://i649.photobucket.com/albums/uu215/warriorsuspension/IMG_0295.jpg

Here is a link on how to set up the drive line angles.

http://www.xjtalk.com/showthread.php?t=7299

[junglejuice]

Wos JJ, you have done a lot of things to this. So if I read this right, you now have an SYE in? If so, then you should be able to draw a straight line on the pinion shaft and drive shaft with no flex on the ujoint. It should look like this:

http://i649.photobucket.com/albums/uu215/warriorsuspension/IMG_0295.jpg

Here is a link on how to set up the drive line angles.

http://www.xjtalk.com/showthread.php?t=7299

It is now set up that way, it is within 2* but it wasn't always that way, it was set up in the stock manner, ie parallel to the g/box which meant that the rear uni had an angle of around 4-5*.
Could this have caused an issue with the pinion bearing? The rear diff was fully rebuilt earlier in the year....

[4.3LXJ]

If you are not having leaking or noise out of it, then don't worry about it. But that much angle on a CV drive shaft would likely give you some vibes. Check all your u joints and make that angle as straight as possible. I am going to hazard a guess here on the vibes under acceleration. Depending on whether the 2° is up or down, if up you may be flexing the springs enough to push the pinion angle to 3 or 4° and then straighten it to perhaps only 1° under deceleration.

[junglejuice]

If you are not having leaking or noise out of it, then don't worry about it. But that much angle on a CV drive shaft would likely give you some vibes. Check all your u joints and make that angle as straight as possible. I am going to hazard a guess here on the vibes under acceleration. Depending on whether the 2° is up or down, if up you may be flexing the springs enough to push the pinion angle to 3 or 4° and then straighten it to perhaps only 1° under deceleration.

It is facing 2* upwards at the moment but a few days ago it was 6* less so around 4* down, all still the same...

[junglejuice]

Well I swapped the axles even though they looked ok I thought I need to start eliminating some things as I gotta tow my trailer soon and if something is on the way out I need to find it.
So I took it for a run....

Still the same!!!!!!! Arghhhhhhhhhhhhhh!!!!!!!!

I am racking up heaps of k's testing this and it is driving me insane so on the way home I took it for a run near to my house as it is making some noise lower down that should be detectable at a lower speed.
Well even at 80~ I can hear it so I don't need to hit the motorway so that is a start...

So 2 transfer cases, 4 tailshafts (2 stock rears and 2 front DC shafts) and still the same, different pinion angles, different ride heights, different wheels & tyres all freshly balanced, different weight oil in the rear diff, different axles and all exactly the same (there was a slight shimmy when using the stock tailshafts that the DC shafts eliminated) so on the way home I thought I need to think differently and try some elimination (electrical fault finding is part of my job) so I thought why not remove the front tailshaft and at least eliminate the front end......

Front tailshaft out, noise goooooooooone!!!!!!!

I am going to try a different front DC tailshaft in the front as the one I removed has some play in the slip joint but I am guessing it is in the front diff, at least I can concentrate on the correct end of the car now!!!!!

[junglejuice]

I have had the original (tight slip joint) DC tailshaft soaking in penetron and it is still firm but better so it is back in as the is zero play in the slip joint.
When I was putting it back in I decided to remove the spare DC tailshaft that I had fitted to the rear and fit it to the front to see if it is the front DC shaft or the diff as the front DC shaft has a moderate amount of play in it, well while I was bolting it to the pinion yoke I found the problem.
The front pinion is loose, it has end float as well as sideways movement so I tightened the pinion nut some more but to no avail, so it is either a bearing collapsed or something worse.
I built the diff 2 yrs ago so if it is from bad set up it has taken 2 yrs to chew out the bearing.
Tomorrow I might have a looksy inside and see if there is any signs of damage to the gears etc (hope not) or if it is just the bearing.
I have offset balljoints in the front on both sides with the drives side just being used for caster and the passenger side used for caster and camber, I don't know if that has had any affect on things or not.....

[junglejuice]

Problem sorted, I stripped the front diff today expecting to find collapsed bearings and worn gears as it has been making this noise for over 8000k!!
Drained the oil, no excessive metal or contaminants, checked the crown wheel, looked just like a new one (well almost), pinion gear also looked excellent.
Found 2 problems, firstly I was able to lift out the centre by hand, without spreading the housing!!!
Secondly as expected found there was excessive play in the pinion, but to my amazement the bearings looked like brand new.
So I removed 1 x 0.010 shim which affects the bearing preload without affecting the pinion depth, then I torqued up the yoke, all sweet.
I then measure the backlash which was still the same as it was when I built it but I had too little carrier bearing preload hence lifting out the carrier without need to spread the housing so I added a 0.005 shim to one side which has too benefits, firstly it adds a little more preload as well as reduced the backlash by approx 0.002.
Re-assembled with the tail shaft and took it for a run, all sweet now up to 120kmh!!!!
This was the first diff that I have built so I am not surprised it wasn't 100%, I am much more confident now after helping to set up my rear d35 with guidance and instruction, lucky for me all the parts were ok....

Thanks for all the suggestions..

[denverd1]

how hard is rebuilding the differential? i'd like to put a locker in and would like to rebuid it while i'm in there. glad you found the issue.

[4.3LXJ]

how hard is rebuilding the differential? i'd like to put a locker in and would like to rebuid it while i'm in there. glad you found the issue.

Rebuilding a differential is not something you should try without knowing how or the right tools. It requires a dial indicator, torque wrench, bearing puller and press. If you want a locker, you can install a lunchbox locker without all those tools.

[junglejuice]

You also require a housing spreader.....

[cantab27]

You also require a housing spreader.....

we made one ...will throw up a pic if i remember...didn't need it to remove front diff when i change axle seals.....

[LizardRunner]

Like Steve says, rebuilding a Diff. is tool intensive and tolerances are very important. Get one thing wrong and your gears will do very bad things. This little thing I put up might be of great help to your decision making process. http://www.xjtalk.com/showthread.php?t=5842

[denverd1]

ok. Thanks for input. I've rebuilt an engine and consider my mechanically inclined, but this may be more than I'm ready for. Got the leaky diff seal replaced in the front and was told the pinion was "loose". tightened the nut, but it may need a rebuild before too long.. good info guys.

[junglejuice]

I built my own spreader which I have used on the front and rear diffs, worked a treat and easy to make....