Hi,

I have a 2003 automatic 2.5l model with 46k miles on it. I was told by a jaguar specialist that the “AWD unit is noisy. Requires replacement or refurbishing”. What I hear is that it rumbles/growls at the rear upon accelerating past 15mph. It starts when the accelerator pedal is pressed and held to gain speed and stops when the pedal is released. The front side of the car is quiet.

The AWD unit to my understanding is at the front and therefore I am not sure that a rebuild or refurbishment will fix what I am hearing in the back. The specialist’s comment therefore might not be related to my problem. Any opinions appreciated.

Many thanks

 

I want you to try something for me. Find a good size parking lot that is empty. Start driving in a big circle (large enough that you can get up to a speed that the noise will occur). Start going in one direction and see if you can get the noise to happen? IF yes, same speed or did it occur at a higher speed. Now, turn around and do the same thing turning the other way. Did one way have the sound pretty much go away or start at a much higher speed? If so, the direction that you were turning is the side of the car that has the issue. This would most likely indicate either a bad CV joint or the hub on that side is going.

If the noise was consistent with what you have been seeing and didn't seem to change when driving in 2 different directions, then I would say you want to get under the car and put your hands on the rear drive shaft (about under where the rear passengers would put their feet). Grab the driveshaft and attempt to move it in a bunch of different directions. Did you get it to move? If yes, your problem is the carrier bearing in the rear drive shaft and that needs replaced. If you didn't get movement, then try and twist the driveshaft. Do you get movement or is it pretty solid? If you get movement, then odds are you need a new driveshaft as one of your U-joints is going.

If all of this has checked out good, then the final check is to take the car out for a drive for about 15 miles (25 km). PUll the car into the drive way and then get your hand near the rear differential. Is it warm (ie, a little bit warmer than the surrounding metal) or is it hot (like, if you put your hand on it, you would most likely burn yourself)? If you are saying hot, then odds are your rear differential has either lost all of its lube or it is self destructing and you are hearing metal eating itself.

 

+1 to "guru" Thermo's advice. If it is indeed one of the rear hubs, look up and read my post on the replacement I just did on my right rear hub. Mine was noisy and in a tight turn in our ubiquitous canyons here in Utah, it went dead silent turning to the right and Thermo told me it was my right rear, which it indeed was.

 

Thank you for those suggested interesting experiments. Unfortunately I was not able to execute them as requested. Firstly, here in the UK the car parks usually have little islands and partings so that it is not possible to turn circles. At least not anywhere near where I live. Instead I did some roundabouts and long left turns on the roads and the sound does not appear to change based on direction.

Further inspection shows that the sound is all about acceleration, not speed. When moving off and and slowly building RPM from 0.75 (x1000) towards 1.5 and 2, the droning/growling starts quietly at 1.5 and grows in loudness towards 2. When the acceleration pedal is only touched very lightly to keep the speed and RPM constant, at any speed or RPM, there is almost no droning noise or very faint, almost hidden under normal tyre noise. A slight pressure on the pedal and it starts getting noticeable as RPM jumps. A sudden press of the accelerator, 25%-50% down, results in the most audible almost knocking sound whilst the RPM needle is at 3 or going towards 4. Higher RPM has a nice V6 sound which hides all the other noise.

There is no droning when the accelerator pedal is not pressed, at any speeds or moving directions.

The car is RHD and the noise feels like it is far away in the back, all the way to the right side.

I will attempt to touch the differential when it is not wet outside. As to the driveshaft, I don’t think I can reach it without raising the car and I do not have the tools to make that happen.

Many thanks

 

This is where spending $100 USD may be money well spent. Any mechanic can look at the car and figure out if it is a U-joint or rear differential (which is what it is sounding like). As for the right hand turns, try doing a few on/off ramps on to a highway. Just something that has a sweeping turn for a bit that you can hit at 25+ kph. If anything, try to diamond the turn a little bit by going a bit straight then making a sharper turn and then going straight again to make what could be done in one gradual turn. What you are trying to do is unload a wheel a little bit to change how much pressure is on the bearing. You lighten the load, it can really change how the noise is generated. But, because you are talking about it changing going straight, this makes some things a bit less likely.

 

I can certainly ask a shop to look at those two things you mention.

Yes, going straight or turning and releasing the accelerator pedal makes the sound disappear. The car basically sounds good at all points where the accelerator is not being pressed.

 

If I may add a funny comment: If you are looking for a place in the UK where to drive circles, go to Coventry in the Midlands: There is an endless number of roundabouts in Coventry, plus the complete city inner CBD of Coventry is surrounded by one big roundabout - just like the M25 around London. After working for Jaguar in Coventry for 1.5 years, the tyres on my German car were pretty much worn on the outer edges of the tyres on the LEFT side, which never happened before, as the few roundabouts in Germany are obviously being used anti-clockwise (traffic on the right side).

Obviously driving the roundabout in Coventry (or GB) in the counter-(anti-)clockwise direction is a problem - maybe in the middle of the night, when no one else is driving?

PS 1: ...and it gets real funny, when the police spots you in the middle of the night driving anti-clockwise in the roundabout and you have to explain to them that you have to test your CV joints and bearings on the left side as well...

PS 2: ...and I am not sure, in which kind of "enclosure" you would end up - the standard one, or the one with the extra rubber padding...

 

Roundabout.............what roundabout?




I think you might have a few new rear end noises during and after that......

 

Thank you very much for those thoughts. I am in the North side of the country and it is quite far away to Coventry! But I will keep that in mind.

The car in question was featured in this test drive by the way. You might hear some of the droning in the video:

https://youtu.be/LicHKOCnr74?feature=shared