High speed vibration

[leorest]

Just been out for the first decent blast since replacing the driveshafts.
I was secretly hoping that this would have cured a vibration I have had since getting the car in 2000.

The symptoms…
At "normal" motorway speeds if you dip the clutch you can feel a vibration which comes and goes instantly with the clutch.
It also happens when the drive train is slack i.e. neither accelerating nor decelerating.
The slightest acceleration/deceleration damps the vibration.

Driveshafts, suspension, bushes, and wheel bearings are all ok by my inspection and it's just got through a MOT where I asked the bloke to give the back end a really good going over. I've also inspected the prop to make sure it hasn't lost a balancing weight.

I think this can only leave the prop and its UJs, the diff (hope not!), and the output end of the gearbox.

I plan to have the prop reconditioned by Proptech who did an excelent job with the driveshafts but this has to wait till I replace the exhaust manifolds which are crumbling into nothingness, which in turn has to wait till I build the garage. Frustrating!

Does anyone have experience of props out of balance or prop UJs failing and do they exhibit the same symptoms as above?

NOTE to self: re-torque drive shaft nuts before next run!

Regards,
Leo

[rev-erend]

Here's an easy one for you to try ...

Elinate the wheel / tyres from the problem area..
swap wheels from front to read ..

Does the problem disappear !

Many alloys get buckled or are eg shaped - causing a
sensation at high 'motorway' speed.

My Focus - has a rear wheel with a slight run out (buckle) .. it's aweful if it's on the front axle but tolerable on the rear axle - some road surfaces make it feel real bad at 70~80 mph..

If I jack the rear and spin wheel - I can see it's buckled !

Give it a go !

[leorest]

rev-erend said:

Here's an easy one for you to try ... Elinate the wheel / tyres from the problem area.. swap wheels from front to read .. Does the problem disappear ! Many alloys get buckled or are eg shaped - causing a sensation at high 'motorway' speed. My Focus - has a rear wheel with a slight run out (buckle) .. it's aweful if it's on the front axle but tolerable on the rear axle - some road surfaces make it feel real bad at 70~80 mph.. If I jack the rear and spin wheel - I can see it's buckled ! Give it a go !

Thanks for that one Rev. It's a good test but unfortunately I omitted to say, I've swapped fronts with rears and also had them balanced and since then I'm on my second set of tyres and the problem has stayed the same throughout. I'm as sure as a sure thing having passed sure exams with merits that it ain't de wheels.

I think the biggest clue is that the vibration switches on and off with the drive train being slack or not. We really are talking about extremely light acceleration or engine breaking damping it right down.

It's not huge vibration but it is there and it's annoying and it can't be good. Something's gonna be stressed by it and that's not just me! A friend of mine had a diff causing vibration on an Elite, which resulted with a fractured hydraulic line giving him an interesting journey back from Le Mans sans breaks!!

Any other thoughts?
Leo

[dickymint]

I'm probably a million miles off the mark here! I recently had a vibration that could be felt throgh the gear knob and was worried about some mechanical breakdown. At the same time i was trying to cure a tuneing fault (missfire). After fettling out the tune problem all signs of vibration now gone!

[paul gotts]

I had a vibration problem on the 400 earlier this year - lifting of at c. 90mph in top would cause a distinct buzz from the back end, as would re-applying the throttle afterwards - like slack being taken up. Another symptom was that a relatively large amount of movement of one of the roadwheels (both off the ground if you've a LSD) would be needed before I saw the prop rotate. Dropped the diff out and had it rebuilt - one broken part inside which meant the LSD was not working properly, and the bearings were worn. Also, worth checking that the pinion bearing nut (behind the flange on the diff to prop joint) has not slackened. If it has, it really is a diff out job, because the preload on this bearing is set through a crush washer, which means that even if you re-tighten the nut later, it will not necessarily give the proper load on the bearing.

[leorest]

paul gotts said:

I had a vibration problem on the 400 earlier this year - lifting of at c. 90mph in top would cause a distinct buzz from the back end, as would re-applying the throttle afterwards - like slack being taken up. Another symptom was that a relatively large amount of movement of one of the roadwheels (both off the ground if you've a LSD) would be needed before I saw the prop rotate. Dropped the diff out and had it rebuilt - one broken part inside which meant the LSD was not working properly, and the bearings were worn. Also, worth checking that the pinion bearing nut (behind the flange on the diff to prop joint) has not slackened. If it has, it really is a diff out job, because the preload on this bearing is set through a crush washer, which means that even if you re-tighten the nut later, it will not necessarily give the proper load on the bearing.

Oh dear! I think LSD rebuild is going to be more expensive than a prop!!!
This sounds like a close match to my symptoms but there is a subtle difference.
Just so I understand completely, and please correct me if I have misunderstood…
---
¦ Paul Gotts' symptoms
¦ Cruising at 90 without vibration.
¦ Lift off gives vibration.
¦ Re-applying throttle gives vibration (this implies that the lift off vibration only lasted a short time?).
---
¦ Leo Rest's symptoms
¦ Cruising without vibration.
¦ Lift off lightly (or dip clutch) gives vibration (this vibration slowly drops with road speed).
¦ Re-applying throttle stops vibration, or lift off enough to give slight engine breaking stops vibration.
---
Shortly after purchasing the car (years ago) I returned it with a query about high-speed constant vibration and they rotated the prop 180 wrt diff end. This seemed to solve the problem but much later I realised that it had only changed the symptoms from constant vibration at high speed to that described above.

paul gotts said:

Worth checking that the pinion bearing nut has not slackened.

How do you check this?

paul gotts said:

Another symptom was that a relatively large amount of movement of one of the roadwheels would be needed before I saw the prop rotate.

How much movement is acceptable? When I returned the car for the original vibration problem I pointed out the diff play, but was told that this is normal and there has to be some play for it to work. I accepted this, as they were a reputable specialist.
Sounds like I need to buy a manual that covers the diff in detail. Can anyone suggest the best book?

Thanks for all of the input.
Keep it coming,
Leo

[rev-erend]

Another idea - visual inspection.. of the moving parts.. you will need a friend to help..

Car nose to wall - rear on axle stands 2 * trolley jacks to re-compress rear suspension (to remove slack) .. 1,2,3,4th gear..

Visually check drive shafts & prop for run out with inspection lamp .. & listen to diff (screw driver to ear to diff) for noise !

Needless to say - if you do this you gotta be bloody careful.. no loose clothing near anything that moves..

[leorest]

rev-erend said:

Another idea - visual inspection.. of the moving parts.. you will need a friend to help.. Car nose to wall - rear on axle stands 2 * trolley jacks to re-compress rear suspension (to remove slack) .. 1,2,3,4th gear.. Visually check drive shafts & prop for run out with inspection lamp .. & listen to diff (screw driver to ear to diff) for noise ! Needless to say - if you do this you gotta be bloody careful.. no loose clothing near anything that moves..

Sounds like a good test.
I'll be needing some bravery pills then.
Standing 6 feet behind an A series Midget doing a ton on a rolling road was scary enough. Doing something similar whilst lying underneath the back end?
I might pay someone else to try it
Leo

[noahstvr]

It sounds like a problem I had with an Alfa years ago,It turned out to be the pinion bearings in the diff. A common problem with this car according to the garage that serviced the car. The cause is when the pinoin gear has no load (no power on no engine braking)It has tendency to ride up and down on the ring gear. This causes a vibration and a "pinion rumble"Many vehicles have this condition however in this type of vehicle you are sitting on top of the diff and the condition is amplified. At the time I had the bearings replaced It helped but diden't cure the problem completly. The noise was only detectable with the Hood up. Good luck G.K.

[noahstvr]

It sounds like a problem I had with an Alfa years ago,It turned out to be the pinion bearings in the diff. A common problem with this car according to the garage that serviced the car. The cause is when the pinoin gear has no load (no power on no engine braking)It has tendency to ride up and down on the ring gear. This causes a vibration and a "pinion rumble"Many vehicles have this condition however in this type of vehicle you are sitting on top of the diff and the condition is amplified. At the time I had the bearings replaced It helped but diden't cure the problem completly. The noise was only detectable with the Hood up. Good luck G.K.

[paul gotts]

---
Shortly after purchasing the car (years ago) I returned it with a query about high-speed constant vibration and they rotated the prop 180 wrt diff end. This seemed to solve the problem but much later I realised that it had only changed the symptoms from constant vibration at high speed to that described above.

paul gotts said:

Worth checking that the pinion bearing nut has not slackened.

How do you check this?

paul gotts said:

Another symptom was that a relatively large amount of movement of one of the roadwheels would be needed before I saw the prop rotate.

How much movement is acceptable? When I returned the car for the original vibration problem I pointed out the diff play, but was told that this is normal and there has to be some play for it to work. I accepted this, as they were a reputable specialist.
Sounds like I need to buy a manual that covers the diff in detail. Can anyone suggest the best book?

Thanks for all of the input.
Keep it coming,
Leo

[/quote]

To check whether the pinion bearing nut has slackened, you need to remove the 4 bolts securing the prop shaft flange to the diff flange. Move the prop flange out of the way (you dont need to disconnect any other part of the prop)so that you can see the large nut inside the diff. If you've got oil running out, chances are the nut is loose. Try getting a socket on it and see how much torque is needed before you get movement of the nut. From memory, when re-building these things, the right figure is something around 100lbs ft.Check in the Jag XJ manual. If you get movement at much less than this, its likely the nut has slackened. You need to do this with the handbrake on to prevent the wheels turning.Apparently they are prone to loosening. As far as how much slack is ok in the diff itself, I seem to remember that I had to move the wheeel something like an inch at the outer edge to get the prop to move. Your symptoms do sound very like my own, although my diff had done c. 130K miles at this point, so it was to be expected. Had been getting worse over a couple of years, but what prompted the rebuild was the fact that the pinion nut had loosened (twice).

[leorest]

paul gotts said:

Check in the Jag XJ manual

Which is the best manual for the LSD?

One of the XJ ones listed here?
www.bentleypublishers.com/resource.htm?subject=9

Or one of the Haynes ones listed here?
www.haynes.co.uk/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10001&storeId=10001&categoryId=14515&langId=-1&parent_category_rn=10215&top_category=10001
-
Haynes Jaguar XJ12, XJS and Sovereign; Daimler Double Six (72 - 88) up to F

-
Haynes Jaguar XJ6 and Sovereign (Oct 86 - Sept 94) D to M

-
Haynes Jaguar XJ6, XJ and Sovereign; Daimler Sovereign (68 - Oct 86) up to D

-
The full title and/or the ISBN number would help a lot

paul gotts said:

I had to move the wheel something like an inch at the outer edge to get the prop to move.

From memory I think mine is about a quarter of that but you can notice the backlash when driving by accelerating then lifting off repeatedly.
If it is the nut loose, am I risking some sort of catastrophic failure if I continue to drive on it?
Either way I would obviously need to tighten it up ASAP.


Questions, questions and more questions…
Thanks for all of your time.
Looks like I'm going to be getting some TVR oil under my fingernails soon!
L

[paul gotts]

leorest said:

paul gotts said: Check in the Jag XJ manual Which is the best manual for the LSD? I honestly can't remember, as I flicked through one at the local library. I think most of these models used the same diff. - a Salisbury 4HU Powerlok (if LSD). From memory I think mine is about a quarter of that but you can notice the backlash when driving by accelerating then lifting off repeatedly. If it is the nut loose, am I risking some sort of catastrophic failure if I continue to drive on it? Either way I would obviously need to tighten it up ASAP. I would check the nut before too long, although I would think that before any major failure the noise/vibration would get much worse. It's fairly easy to check the nut. When I found mine loose the first time I removed it completly, degreased it and applied thread lock, and it still slackened again - maybe because you can never get the proper torque against the crush washer once its been crushed.

[leorest]

paul gotts said:

When I found mine loose the first time I removed it completly, degreased it and applied thread lock, and it still slackened again - maybe because you can never get the proper torque against the crush washer once its been crushed.

So there is no locking scheme then?
Lock nut, nylock, aerotight, wired etc..

I guess to get to the nut I'll need to drop the exhaust at least a few inches?

Thanks
I feel like I've got something posative to try.
L

[paul gotts]

leorest said:

paul gotts said: When I found mine loose the first time I removed it completly, degreased it and applied thread lock, and it still slackened again - maybe because you can never get the proper torque against the crush washer once its been crushed. So there is no locking scheme then? Lock nut, nylock, aerotight, wired etc.. I guess to get to the nut I'll need to drop the exhaust at least a few inches? Thanks I feel like I've got something posative to try. L

No sign of any thread lock when I removed mine. Its quite a large nut but I guess if you hunt around you could find a locking version. No space to lockwire anything. And you dont need to remove the exhaust at all, just drop the diff end of the prop and wedge it out of the way. Its pretty straightforward.