Hi, I've got a car that sounds similar to this, except that the howling
(like a gail) is most pronounced under light throttle conditions and at
all road speeds.

The vibration I get starts at the exact moment the car changes into
overdrive top (54mph in my case, and basically its a direct drive 5th
gear with out the torque converter to give better mpg). This gear
change is difficult to detect as it happens at such low revs (around
2000rpm). As you say the vibration is bad at first but as speed rises
fades a bit.

I also haven't had my car long, but did get it up on axle stands a
couple of weeks ago to find there was oil leaking out the diff and that
I could replicate the howl, running the car in D and revving the
engine, ab-it momentaraly.

I also intend to change the diff bearings as soon as the engine is back
together!

Whilst under the car (not running) I grabbed on the the rear of the
gear box and was able to move it up and down quite a distance (about
3/4in in both directions), I'm aware that there is a spring in this
system but wonder if at high torque low rev conditions that excess
movement here could bring about a vibration?
I can feel it through the steering a little which suggests to me that a
large mass is moving around inside the confines of the
engine/transmission bay?

Any thoughts anyone on what I've said or our problems?

Much appreciated

Mr Smooth

Hi I not long had my first xj40 and it seems that there are some
similar problems.

I've not cured them at the moment but I'm investigating, and this is
what I've found:

Firstly the howling noise, mine is definitely connected to the diff as
I've had the car running on stands in the garage (a little nerve
wracking) and listened to the rear end whist in D. Prodding the
throttle reproduced the howl momentarily (which was loud in the
confines of a garage). I'm intending to replace the bearings first in a
bid to fix this prob, but I'm not convinced as the howl sounds gear
related and there is oil leaking from all the in/outputs, suggesting
that it may have covered many miles low on oil (it was a reps car and
covered 65k in 2.5 years!).
The main difference between my noise and yours is that mine makes the
howling noise (amongst other more subtle noises)  at any road speed,
most notably around town at light throttle when the cabin is quietest.
Could be the same/similar thing? I'm not sure...

On to the vibration. It is interesting that you should say it occurs at
50mph as this is about the point (out of sport mode of course) that the
gearbox changes to overdrive 5th and locks out the torque converter
(this gives better cruising mpg as there's no power lost though the
auto box). The gear change is very smooth, or course, and easily missed
(check the rev counter as you approach 50). I have noted this is the
exact time I get my vibration, which also lessons to a small extent the
faster I drive.
I've also felt the vibration through the seat/transmission tunnel and
steering wheel at the same instant, suggesting to me a large mass is
moving around, enough to enable its effect to be felt through the
wheels.

During my fiddling under the car I grabbed the gearbox tail and heaved
it around, noting that it moved around easily (once you get over the
inertia of the thing) up to about 3/4 of an inch from center. I know
there is a spring based mount located here and that they are prone to
collapse after a while. I'm not sure what its supposed to feel like?
Anyone?

Could it be that when the box changes up we are experiencing a low rev
high torque situation, just enough to cause the whole drivetrain to
wiggle about off centre?

Hope this has given you some food for thought?

If there is any one out there who works on these cars regularly, surely
you've come across this before?

Best regards

Mr Smooth

Hi I not long had my first xj40 and it seems that there are some
similar problems.

I've not cured them at the moment but I'm investigating, and this is
what I've found:

Firstly the howling noise, mine is definitely connected to the diff as
I've had the car running on stands in the garage (a little nerve
wracking) and listened to the rear end whist in D. Prodding the
throttle reproduced the howl momentarily (which was loud in the
confines of a garage). I'm intending to replace the bearings first in a
bid to fix this prob, but I'm not convinced as the howl sounds gear
related and there is oil leaking from all the in/outputs, suggesting
that it may have covered many miles low on oil (it was a reps car and
covered 65k in 2.5 years!).
The main difference between my noise and yours is that mine makes the
howling noise (amongst other more subtle noises)  at any road speed,
most notably around town at light throttle when the cabin is quietest.
Could be the same/similar thing? I'm not sure...

On to the vibration. It is interesting that you should say it occurs at
50mph as this is about the point (out of sport mode of course) that the
gearbox changes to overdrive 5th and locks out the torque converter
(this gives better cruising mpg as there's no power lost though the
auto box). The gear change is very smooth, or course, and easily missed
(check the rev counter as you approach 50). I have noted this is the
exact time I get my vibration, which also lessons to a small extent the
faster I drive.
I've also felt the vibration through the seat/transmission tunnel and
steering wheel at the same instant, suggesting to me a large mass is
moving around, enough to enable its effect to be felt through the
wheels.

During my fiddling under the car I grabbed the gearbox tail and heaved
it around, noting that it moved around easily (once you get over the
inertia of the thing) up to about 3/4 of an inch from center. I know
there is a spring based mount located here and that they are prone to
collapse after a while. I'm not sure what its supposed to feel like?
Anyone?

Could it be that when the box changes up we are experiencing a low rev
high torque situation, just enough to cause the whole drivetrain to
wiggle about off centre?

Hope this has given you some food for thought?

If there is any one out there who works on these cars regularly, surely
you've come across this before?

Best regards

Mr Smooth

Hi I not long had my first xj40 and it seems that there are some
similar problems.

I've not cured them at the moment but I'm investigating, and this is
what I've found:

Firstly the howling noise, mine is definitely connected to the diff as
I've had the car running on stands in the garage (a little nerve
wracking) and listened to the rear end whist in D. Prodding the
throttle reproduced the howl momentarily (which was loud in the
confines of a garage). I'm intending to replace the bearings first in a
bid to fix this prob, but I'm not convinced as the howl sounds gear
related and there is oil leaking from all the in/outputs, suggesting
that it may have covered many miles low on oil (it was a reps car and
covered 65k in 2.5 years!).
The main difference between my noise and yours is that mine makes the
howling noise (amongst other more subtle noises)  at any road speed,
most notably around town at light throttle when the cabin is quietest.
Could be the same/similar thing? I'm not sure...

On to the vibration. It is interesting that you should say it occurs at
50mph as this is about the point (out of sport mode of course) that the
gearbox changes to overdrive 5th and locks out the torque converter
(this gives better cruising mpg as there's no power lost though the
auto box). The gear change is very smooth, or course, and easily missed
(check the rev counter as you approach 50). I have noted this is the
exact time I get my vibration, which also lessons to a small extent the
faster I drive.
I've also felt the vibration through the seat/transmission tunnel and
steering wheel at the same instant, suggesting to me a large mass is
moving around, enough to enable its effect to be felt through the
wheels.

During my fiddling under the car I grabbed the gearbox tail and heaved
it around, noting that it moved around easily (once you get over the
inertia of the thing) up to about 3/4 of an inch from center. I know
there is a spring based mount located here and that they are prone to
collapse after a while. I'm not sure what its supposed to feel like?
Anyone?

Could it be that when the box changes up we are experiencing a low rev
high torque situation, just enough to cause the whole drivetrain to
wiggle about off centre?

Hope this has given you some food for thought?

If there is any one out there who works on these cars regularly, surely
you've come across this before?

Best regards

Mr Smooth

I have a 2001 XJ8 that developed a vibration at 50mph, and I recently heard
there is a kit available.  I am going to check into it right away, but thot
you might could use the heads up.  Quite a difference in age, I realize, but
who knows...may be the same problem/same chassis.