So I broke down and bought my second XJ6 Last week.
This one is a 1997 XJL my other is a 1996 VDP.
It has 118k miles.

Anyway, This car has a distinct noise coming from the rear end.
It sounds like a low frequency BUZZ or rumble. It increases pitch with speed on the road not engine speed. but it doesn't change with either acceleration or deceleration. And it doesn't get louder or softer. So I'm not sure it's actually the differential. I've never heard a well bearing sound like this because it's not a whirring or whining. there is a distinct "buzz" about it that sounds more like a gear noise. Still it seems to be coming more from the drivers side of the vehicle than the center.
I don't hear it at all under 30mph and it turns into a general "hum" at 70. by 80 you can't hear it anymore.

If you accelerate or decelerate there is a brief moment where as it changes over that it disappears. I mean like a seriously brief moment... like a 1/10th of a second or less.

It has never had a leak and the differential is clean no signs of leaks. I had the fluid replaced about 500 miles ago and it was full. I didn't notice any discoloration in the fluid and the new fluid didn't change the sound at all.

The sound does increase slightly when warm. In other words the first few minutes of driving (it's 30deg outside today) you don't hear anything. but after about 2 or 3 minutes you notice it.

Perhaps I'm being oversensitive because I've heard so many horror stories about rear ends on the X300 but my VDP does not sound like this. So I'm curious if i have a serious problem or just some bearings somewhere?

any help would be appreciated.

 

Have you tried greasing the zerk points on the half shafts?

 

I haven't but I can't find any points on the rear to grease....
A local shop just told me the bearings were bad but they want $700 to replace all of them so I'm thinking of doing it myself... but I'm still not sure that's the problem.
are you talking about grease points on the U joints on the short shafts?
I haven't seen any of them either but I can look again.

 

This should be the first thing to try (easy fix). You have 4 lub points, one on each half shaft end. You must rotate it to access the lub points.
Then, worn wheel bearings may also be the culprit. I had to replace some (not all at the same time). The noise from one of them was very different than the usual humming which increases with speed. I took a long time to accept it to be a bearing (replaced tires, changed dif oil,.... etc). But it was a bearing, yes.
Good luck.

 

It could be a loss of preload to the pinion bearing.
Have a look at this site. www.bernardembden.com/xjs/diff/index.htm
Dennis

 

Steve,

One method of tracking down your noise is to raise the car on a lift or support the rear end with jack stands so the rear tires are above the ground and securely chock the front tires both in front and back of each tire. Start the engine and put the transmission in Drive and the rear wheels will begin to spin.

Working from alongside the car (not under it) as much as possible, use an inexpensive mechanics stethoscope (less than $20 at any chain auto parts store) to carefully probe all the likely suspect areas, taking care not to touch any rotating parts with the stethoscope probe:

Wheel bearings
Differential output shaft bearings
Differential pinion (driveshaft input) bearings
Driveshaft center bearing

If all of those are quiet, suspect a U-joint.

The wheel bearings and diff output shaft bearings are relatively easy to replace (a press is requred for the output shaft retaining collars). Replacing the diff pinion bearings requires removal of the diff/independent rear suspension from the car.

I can give you links to photos of all this work once you identify the source of your noise.

Cheers,

Don

 

Thanks!
I found the lube points.
Hidden under years of old grease.
Anyway, Lubing them had a huge impact on the rear end noise.
But it is not gone. I guess I have multiple sounds blending together....

 

That is a very cool web site.
I'm very tempted to try it.

 

Ok well it wasn't the wheel bearings or the shaft u joints. It wasn't the pre-load on the Front of the diff... I did all that... So in the end I replaced the entire differential. All running quiet now. I got a diff from coventry west. Good price. Nice guys to work with.

 

We also had a differential noise that was quite loud. Recently purchased car and started by replacing inner and outer hub bearings on both rear hubs. PO had replaced in the recent past but had assembled with new bearings but left badly worn races, and had reversed the spacer and smaller shim order. Also found one outer u joint was completely shot. Pivot shaft bearings were OK. Reassembled thinking we had solved the noise problem, but not much change. Fearing the worst, we took car to a local independent Jag shop for a diagnosis. After a test drive and up on the lift, they said it appeared to them it was definitely pinion / gear noise and would replace with a used donor rear end for about $1200. Thought we might as well try replacing upper (inside) u joints and output shaft bearings before dropping the rear suspension. Replaced the drivers side output shaft bearing ( u joint was fine), and went on a test drive before doing the other side and presto! noise was almost completely gone. Will replace other side this week. Jurid bearing has some fine visible cracking, so it will be on the list for the future.
Thanks to those who had mentioned output shaft bearings as a possible culprit for rear end noise in previous threads. My son in college was impressed we solved without having to drop and replace the differential as recommended by the shop.
Now on to the sticking throttle body.....

 

Hey we had that problem and I solved it.
I'm not sure I can describe what I did in text....
First we took the throttle body apart and cleaned it.
Then re-assembled and greased the shaft.
This only worked a little while because the shaft it's self and the housing are worn.
I found that if you pull up on the shaft a little when it's stuck it will free up.
So I shifted the angle of the cable so it was a little higher.
I did this by putting a 1 inch spacer under the cable mounting bracket.

This caused a slight upward pressure on the cam that the cable wraps around and lifts the shaft up off the throttle body just a tiny bit. Problem solved.

I don't know if that makes any sense.

But I keep the shaft lubed now as well.
When it drys out over time it rubs and wears the shaft.

The ever so slight upward pressure changes the angle of the pull and
lifts the throttle body shaft away from the binding point.

 

Well in the end it required replacing the rear end (5/2015)... the inside was pretty worn too... I guess someone had run it without lube for a while before I purchased it. It was a pretty expensive repair. like 3K... anyway long story short we had a terrible time aligning it. In the end there is a large shim between the shafts and the rear end. mine was 7 millimeters it needed to be 6.5 millimeters This is one huge 5 inch diameter washer looking thing. We tried to use body shims but they came out... These shims are pretty hard to find. Each car is different it seems. When the rear end isn't aligned right after replacing the rear end then it never drives right. The car will dart and drift. But all fixed now and much quieter. And finally drives straight.

 

I had the same issue with the rear end noise that your described on my sold 1997 XJ6 many years ago. The cause was low in oil and resulted in damaged differential. I was fortunate to purchased the entire complete rear frame with differential, shock etc for $300.00. I dropped then entire rear frame and installed. My brother is a Jaguar Master mechanic. I recalled that he indicated this is a frequent damage to due low oil. Jaguar dealer quoted $3,000.00 plus to replace with used unit. I recently purchased another 1997 XJ6 with extreme low mile. The first thing I did was drained and refilled with new differential oil to prevent this mishap. It was a quart low in oil.

 

I believe the rear end takes around 2 quarts, being a quart low is not good!

 

Frustrating. I have 2 other XJ6's with NO rear end problems but when they start looking dirty you have to replace the seals early so they don't leak. People just don't take care of things sometimes. Still even with the repair I'm only into the 97 for about 6K and I've put 80K miles on it so I'm at less than 10cents per mile with a fabulous car to drive!!!