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[Sooty Si]

Ok, so I've replaced both front wheel bearings and the accompanying noise is gone and I've just drained the goopy old crap oil (no metallic debris) out of my diffs and transfer case today, and refilled with the good stuff.

Still got an odd noise though. If I've got my foot on the accelerator pedal, all is quiet and normal, but after a mile or two, if I release pedal, i.e. to slow down or coast a bit, there's a noise, not really a droning sound, but, kind of hard to describe, like a rough bearing maybe? Goes away again if I gently press the accelerator pedal. Comes from the front end and sounds to be nearer the middle-offside front. Both front driveshaft CV joints are good (nearside is new, offside replaced recently). There doesn't appear to be any play in the front propshaft. 

Anyone got any ideas?

[gregwho]

Could it be the diff bearings themselves?  I know that mine are starting to whine and im at about 100k.  The shop i'm thinking about taking them to for a rebuild says that the bearings can go from 75k onwards, and others can last much longer.  How many miles have you done?

If it is that, I cant explain the lack of any shavings in the oil though    the noise of mine does seem to differ as the oil warms up, and does change tone as I speed up or slow down.

Just a thought, probably a million miles off!

[Sooty Si]

No mate, any ideas are worth considering - thanks for replying. I'm no stranger to mechanics, but this is my first 4x4, having just got it in December so I'm having a steep learning curve as I have to know how things work, and love fixing stuff. I bought it as a project, and this noise (and a non-working heated driver's seat) are all that's left bugging me. Diff bearing make sense, especially if they're "thrust" bearings. Most people seem to have noise on acceleration, but mine's the opposite, on deceleration. Going to have to live with it for a bit, as my Alfa deserves a bit of TLC.

[LairdScooby]

What about the inner universal joints (UJs) on the drivesshafts where they meet up with the front diff? Just a thought? Could be some play in them or possibly they're not perfectly aligned with the flange so giving a bit of vibration?

[Sooty Si]

An update on the noise: Still none the wiser about it's source. When setting off, there's a regular clicking noise fron the front very much like a dodgy CV joint would make, turning the steering in either direction makes it more obvious, but it's still there in a straight line, relative to vehicle speed, and eventually seems to disappear. It's not an irregular click as if a couple of teeth have let go in the diff. All is reasonably quiet at speed until I ease off the accelerator pedal, then the noise described in the previous post begins, definitely not a bearing "howl" or a "whine". If I slip the box into neutral and coast to a standstill, the noise gradually reverts to the clicking sound until the Jeep stops.

I have had the Jeep up on a lift, there's no worn linkages, mounts or bushes (also just passed it's MOT). I can't find any play in the front propshaft (type 3).

I've been scouring the web, reading up on the various noises etc that can occur in diffs and driveshafts, but can't nail it down. My next course of action is I'm going to pop the front diff cover off with the front of the Jeep on axle stands so I can turn the wheels, to see if there's anything obviously wrong in there.

From what I can gather, the "droning" noise on deceleration can be usually caused by incorrect pinion shaft preload, or, worst-case, the inner pinion bearing. But after today's test drive, it's not really a drone (see above). Also, can't really hear anything with the windows down...weird!

So, has anyone here had any experience like this? Anyone got any ideas I can try out before I resort to a costly diff rebuild?

Both front wheel hub bearings are new, LH driveshaft CV joint new and RH driveshaft CV joint recently replaced.

Thanks in advance...

[LairdScooby]

Stone in one of your tyres perhaps? Worn/loose gearbox mount causing gear lver to rattle? Worn/loose steering box mounts causing sterring column U/Js to rattle?

Maybe silly suggestions but if you can't find anything where it sounds like it's coming from then it might pay to look at the "silly stuff".

[bisleywrangler]

Front propshaft uj maybe. My wrangler one used to click at slow speed, it didn't whine though.


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[Sooty Si]

Hmmm, could be worth another look I guess, there was a teensy bit of play in tthe double cardan joint at the transfer case end, wonder if the CV at the diff end could be U/S ?

[gregwho]

If you do end up looking at a diff rebuild, I was quoted about £500 (on a WJ) - its a place on the outskirts of London.  I can dig out the contacts if you want to investigate

[Sooty Si]

No, it's OK thanks. If it needs a rebuild or anything, I'll do it myself. Would just like to know what the source of the noise is. Been posting this on almost every Jeep forum I can find with no joy so far...I live in hope.

[Sooty Si]

Woohoo! I am pleased to announce the "Odd Noise" is gone!

Removed the front propshaft, noise gone. Replaced with a 2nd hand one off eBay, noise still gone. Going to refurb the old one's CV joint and UJ's so I've got a spare, given the absolutely ridiculous prices (£500-£600) for a new one!

 

[LairdScooby]

Yay! Good news!

[gregwho]

Great result!!