FIXED: see lower posts for solution (junkyard diff)

2002 XJR
70,000 miles

this noise occurs any time you let off the gas to slow down
the noise does not occur when you are accelerating

there is also a bang noise when you are going about 20 +-5 mph and hit the gas, it bangs again when you let off the gas at that speed

My theories are issues with transmission, differential, drive shaft, u joints, wheel bearings

Thanks in advance for any suggestions as to what this is!

Video:

 

Can't hear it that good, but could be diff gear, at least there its common that you could get different noises (or no noise with normal driving, and a noise when coasting).

The banging could come from worn bushings of the rear suspension. You can check where the noise is coming from when you put your car in park, and then rock the car back and forth (just via turning a wheel), and once you get some momentum you will probably also hear from where the noise comes.

 

Differential or drive shaft bearing.

The differential, the gear are pressed/meshed together when accelerating and slack off when decelerating. Worn gears, but most likely you would hear the noise all the time.

It really soulds like a bearing noise, with the fluctuation of the noise, just like a bad wheel bearing.

Jack up the rear, placing it on jack stands, start the car, take traction control OFF. Put it in drive and get under the car and listen, if you hear nothing. Have somebody get it up to 25mph and let up off the gas (NO BRAKING) and listen.

That should tell you exactly where the noise is coming from.

SGB

 

Perform a diff bearing check by finding a flat car park and roll the car around at your 'find it' speed in a big arc left and right to isolate the side thats noisy.

Doubtful it's gearbox. There are two big rubber donuts, one at the gearbox coupling and one at the dif isolating the prop, check these and their bolts before anything else for the shunt noise.

 

Thanks very much for the replies, I am going to do these tests tomorrow and see what I can find out.

 

Seems like it's the differential, I jacked up the rear end and ran it up to speed, it makes the noise under both acceleration and under deceleration which is interesting

as far as the knocking noise goes, I did some "swerving" at around 10mph and you can hear it. with the rear end jacked up, I rotated one of the rear wheels and when I stopped rotating it the noise happens. same thing for the other wheel. seems diff related.

I looked at the "donuts" for the driveshaft, I assume that's where the driveshaft bolts to the diff and where the driveshaft bolts to the trans output, visually it didn't appear to be in disrepair.

Video with the rear end jacked up:

is it likely that I need a new diff or are there other components that could be causing this issue?

 

You may not need a whole new diff. I've heard of the output shaft bearings needing replacement without having to remove the diff. I don't have personal experience though. Just thought I'd throw that possibility out there.

 

There is also a Center bearing, but if your are hearing the noise from the differential and not over the center muffler, then you can scratch out that part.

For the knocking noise, put the car in park and move the tire with your foot, see if there is any free play in the flex plate. The flex plate is what the drive shaft bolts too. If theres any free play, then it could well be just the flex plate need replacing.

 

was under the car some more and I noticed the diff seems to have some wet deposits on it like it may be leaking.

the noise seems to be coming towards the transmission, but it is hard to tell, when you are listening on one area it seems to be noisy in another, etc.

I am thinking about doing a differential fluid change, what's the proper diff fluid that I need and is there any special procedure for doing this? I searched the forum but had no luck.

also I searched but didn't come across anything, isn't there some sort of breather on top of the diff that can become clogged?
EDIT: found some threads about diff oil and servicing
Thanks in advance for any assistance!

 

Shell EP 90 - a 90 grade diff oil is the winner. The Breather can get clogged and then forces oil out of the front seal breather, part number is JLM20323.

 

I know its been a while, but I finally decided to and had some time to start working on this issue again. got the car jacked the car up and got the plug out of the differential. there is fluid in there, but it seems a bit low, I'm going to add more fluid tomorrow and see if there's any change in my noise situation

 

Any updates? I'd say my diff is 10k miles away from making this
type of noise on a regular basis. So I am interested in this
issue.

 

talked to several mechanics and they all said it could make this type of noise forever and not be a problem other than the annoyance.

It's pretty annoying but I just turn the stereo up. I'm going to ignore it until it gets louder/worse, hopefully I'll be able to replace my noisy diff with a limited slip diff at some point

 

Noise became much much louder, couldn't even drown it out with the radio, took it to a shop, they diagnosed it as one of the "teeth" inside the diff broke off, car is getting a used diff installed within the next few weeks

 

Thanks for the update !

 

I hope mine doesn't grenade itself, it is making the noise
(currently 102k) and both seals on the thing have started to
leak. So, if I pay/go through the trouble of doing those seals
and it breaks inside, it will be a complete waste! I want to
do a Quaife limited slip but I blew all the money I could have
spent on that on hitting a curb.

Mine is a "Jaguar Genuine Exchange part" installed at 82k
so you would think it could have survived more than 20,000
miles before making stupid whining sounds.

Thanks for the update.

 

nice to hear that car is going to be fixed. as i know this year model xj's are supplied with similar gearboxes as mercedes s class w220. so just in case you can also ask MB guys for an opinion

 

yeah it's a shame that the stock diff doesn't have a very long service life. I took this video as the noise became worse, this is on the highway at about 65 mph. I am not driving the car any more except for the 1 mile trip at 30mph to the shop whenever the used diff gets there. you can hear lots of general 'noise' but you can also hear the constant loud rumble of the diff. Hopefully this can help someone in the future with their diagnosis.

 

Car has had the junkyard diff installed for about a month and (~500 miles) with no problems, and I got my old diff back from the shop, so someday I can have an LSD fitted into my old diff casing.