Howling Diff - getting worried now...

[JON1D]

Glad it was not a strip down. I had weights and dial gauges out on my last diff and at 42,000 miles from a donor it was all in spec with an added bonus it was de-rated so a nice spare xj12 2.88 LSD only requiring an oil change.
I ended up building a near complete refurb rear end hand brake and brakes in lock down as was getting bored. Which I might now decide to sell.     

One good think is the jag Xj diff is fairly bullet proof once set up. That's why they are used in historical race cars. Its good that we can still get any parts after some 50 years being manufactured in various versions.

[Bannon]

Well - today was the day.  Checked my IRS and I reckon all is ok.  The rocking of the wheels looks to me like it's all normal = just a little hint of movement 12/6 o clock position, seems to be at the diff output flanges.
   So, on to the pinion shaft:  propshaft off, have a feel, measure the rotational resistance with spring balance, decide to proceed.
  Make and fit locking tool, place socket on pinion nut and...it's loose.  Loose!  Nearly half a turn later, it goes tight and I continue cautiously until the rotational resistance begins to increase slightly: propshaft back on and go for a drive.  Much improved!  Far less noise, no more clunking.  Success!
   I am going to drop the oil though, replacing it with Castrol TransMax 75W/140.  It's a bit heavier and could reduce noise a bit more, but I think I'm close to normal noise level now anyway, so thanks all for your advice on this.    

[Chris]

You will obviously need the 4 foot bar if you are tightening the pinion nut ,
but go easy as explained in the article.
You may be ok and all is needed is a bit of a tighten due to everything setting down .
Chris

[Bannon]

You can also check  the rotating force of the pinion by using a spring balance and a piece of string.
That was the method I used but would add that the crush washer didn't need replacing .
The other thing that I did was to fill the roll over bar/bars with builders foam to eliminate diff whine
that can be present due to the way the diff is mounted onto the chassis.
I do not have any noticeable whine all though there is slight  whooshing noise  that is coming
from the internal brake discs and pads !
On my right side there is a 4" exhaust outlet 18" from my ear therefore no whinnying !
You don't really need any special tools for these type of checks but you will need a decent 4 foot bar
to hold the flange in place while you release the pinion nut.
Chris.

Spring balance is a very good idea - might well go that route.  I actually filled my roll bar with builders foam last week.  I think it worked, but the noise level is severe so I need to really get to the source of the noise.  I'm feeling fairly confident that the pinion pre-load is the issue.

[Chris]

You can also check  the rotating force of the pinion by using a spring balance and a piece of string.
That was the method I used but would add that the crush washer didn't need replacing .
The other thing that I did was to fill the roll over bar/bars with builders foam to eliminate diff whine
that can be present due to the way the diff is mounted onto the chassis.
I do not have any noticeable whine all though there is slight  whooshing noise  that is coming
from the internal brake discs and pads !
On my right side there is a 4" exhaust outlet 18" from my ear therefore no whinnying !
You don't really need any special tools for these type of checks but you will need a decent 4 foot bar
to hold the flange in place while you release the pinion nut.
Chris.

[Bannon]

Could be the diff pinion bearing at the end of the diff when not loaded and off throttle.

https://bernardembden.com/xjs/diff/index.htm

Explains it better. Diff cover off and blue your crown and pinion will show if the mesh is correct.

The crush washer can be changed in situ but you need a ramp lift.

Thanks Jon, this sounds well worth checking out.  I'll get the propshaft off and check the play in the pinion as the symptoms and noises all seem to point to that.  If I find play,  I'll get set up to tweak it as per the tutorial - with one exception:  I'll buy a suitable Inch-Pound torque wrench/driver rather than hanging weights to measure it.  I'll also check all U/Js and the radius arms for that clunking.

[JON1D]

Could be the diff pinion bearing at the end of the diff when not loaded and off throttle.

https://bernardembden.com/xjs/diff/index.htm

Explains it better. Diff cover off and blue your crown and pinion will show if the mesh is correct.

The crush washer can be changed in situ but you need a ramp lift.

[Bannon]

For the clunking, yes.  But the chattering of the gears - I did notice that from cold, it's pretty quiet for a mile or two - until the oil starts to warm up abd thin out, perhaps.   Maybe I could try a heavier oil - EP140 maybe?

[Happy Jim]

Might not be your diff!

Worth checking all the UJ's (prop & drive shafts) first.

Regards

Jim

[Bannon]

Hi guys,
   My car ran great to the National Kitcar Show and home again - really faultless engine-wise,  but my diff is SO loud.  The noise sounds like the meshing of the teeth - loud and raspy, only goes quiet when not loaded on either throttle or over-run.   I know it's bolted solidly to the chassis, but it's excessive.
  In addition, I now get a clunk when I come on or off the throttle.  I really don't know much about the Jag IRS,  so any pointers or advice?   Thanks in advance.