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Propshaft vibration ... ?


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#1 BogMonster

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Posted 04 October 2005 - 08:50 PM

The other weekend I changed the front springs on the 90 for 90 rear ones to restore a bit of altitude under the bows due to slightly saggy old front springs.

However.....

Having driven it for a while I notice that there seems to be a bit of vibration from something at low speeds under load. I first noticed it when I was towing a broken down 110, and pulling away in first gear with the 110 on a rope behind there was quite a noticable judder. It's less obvious with nothing tied to the back and pretty much disappears once you get a bit of speed up.

What are the normal symptoms of propshaft vibration? I've never suffered from the problem before and as I've said before the old 90 had "90 rear" springs on the front and didn't do it - though those were second hand ones and these are new (so possibly sit a little higher), also these have the ANR2938 isolator rings on top. Does the prop normally vibrate at low speed, or high, when the operating angle of the UJ's is a little too much? The obvious culprit is something to do with the suspension being higher as it wasn't doing it before.

Any experience of lift-related vibrations would be appreciated :)

I hope that if this is the problem I might be able to get away with just taking the isolator rings out - they are about 0.3" thick so will reduce the height by about that much, might be just enough to stop the vibration?

So much for only having to take all the front shockers and stuff off once - famous last words :angry:

Oh well if they have to go in the bin at least the springs were free, glad I didn't have to buy them :rolleyes:

a shame as everything else about the lift is fine, just about what I wanted, but I am not prepared to go to the expense of double cardan props, I'd rather lose half an inch at the front :(
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#2 white90

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Posted 04 October 2005 - 09:05 PM

Stephen
Posted Image
shows the angles of the prop etc, these are too steep.

in lifting it you've altered the castor and made the transfer box UJ steeper with
quite possible the Prop is now protesting.
Tony


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#3 BogMonster

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Posted 05 October 2005 - 12:13 AM

but is it normally worse at low road speeds, or high road speeds?

I would have thought worse at higher speed but on mine it seems to disappear

what is the normal problem with prop vibration?

I could take it off and try it like that but I am lazy :)
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#4 Astro_Al

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Posted 05 October 2005 - 08:39 AM

>"but is it normally worse at low road speeds, or high road speeds?"

Not necessarily, it depends on the geometry and the frequency that you excite it at - so it will vibrate at specific speeds, but not necessarily higher speeds. You should pass through 'bands' of vibration as you accelerate.

Is the problem that the UJs are working at too great an angle (could you just replace them with high angle ones without going to double cardan?), or is the problem that the two faces of the propshaft (the one which mates onto the transfer box output face and the diff pinion mounting face) should (theoretically) be in parallel planes. If you stick to both of these and the prop is correctly balanced, you won't have vibration.

Did the angle of the diff change (i.e. does it now point more nose up or down) when you swapped the springs and bits?

I can't see the pic above - is it just me?

Al.

#5 Guest_diesel_jim_*

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Posted 05 October 2005 - 08:50 AM

I had a similar thing with my 90 (and my Td5 110 recently).

I fitted a double CV front prop to the 90 and it cured it immediately.

my 110 had a nudgebar and 8274 up front, so i stuck in some 90 HD rear springs i had, it lifted it a little too far, about 2.5~3 inches (but it looked a little "front high") and that caused some slight vibes, at low speed. once i speep up to the lightening speeds my 110 tank is capable of (about 80mph flat out) they went away!

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Posted 05 October 2005 - 12:21 PM

And now i have just found this: on eBlag

a disco S2 front double CV shaft! thats what you want Stephen!

#7 Tonk

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Posted 05 October 2005 - 12:23 PM

I can't see the pic above - is it just me?

Al.


nope, cant see it either
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#8 white90

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Posted 05 October 2005 - 01:12 PM

RE:
Is the problem that the UJs are working at too great an angle (could you just replace them with high angle ones without going to double cardan?),


high angle ones allow more movement they do not correct the problem in the first picture, as this is a high angle prop, just allows more travel before the yokes touch
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#9 Astro_Al

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Posted 05 October 2005 - 02:05 PM

You say the angles of the UJ are too steep - why would a high angle UJ not allow this to be ok then? Isn't that what you say it corrects for? :huh:

If the problem is non-parallel faces, then sure, you need to adgust the angle of the axle or fit a different prop which can cope.

Al.

#10 white90

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Posted 05 October 2005 - 02:18 PM

You say the angles of the UJ are too steep - why would a high angle UJ not allow this to be ok then? Isn't that what you say it corrects for? :huh:

If the problem is non-parallel faces, then sure, you need to adgust the angle of the axle or fit a different prop which can cope.

Al.


A high angle prop only allows a greater range of movment it does not fix the problem of one UJ near full deflection and the other running parrallel, this mismatch caused me a lot of wasted /Time and rsache to identify and fix.

castor correction arms make the problem worse BTW
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#11 Astro_Al

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Posted 05 October 2005 - 02:47 PM

Ok, thanks for the clarification, I agree with everything you say - it was unclear that mis-matched alignment angles are the problem. So this one falls into the 'propshaft flange faces are not in parallel planes' category.

In case anyone is interested, this happens because a UJ which is not perfectly aligned (i.e. the axis of the incoming shaft is not the same as the axis of the outgoing shaft) has a non-linear angular velocity through a 360 degree rotation. Since both ends of the propshaft experience this (cos they both have a UJ in), and the variation in angular velocity depends on the deflection angle through the UJ, if the two ends have different angles of deflection they will be trying to turn with different velocities...

I *think* that's right!?! :huh:

If you don't want to change shafts, but need to get rid of the vibration, the only way is to reduce the difference in the angles of the planes of the flanges (to zero preferably).

If anyone spots anything wrong in the above, please let me know! :)

Al.

#12 white90

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Posted 05 October 2005 - 02:52 PM

Ok, thanks for the clarification, I agree with everything you say - it was unclear that mis-matched alignment angles are the problem. So this one falls into the 'propshaft flange faces are not in parallel planes' category.

In case anyone is interested, this happens because a UJ which is not perfectly aligned (i.e. the axis of the incoming shaft is not the same as the axis of the outgoing shaft) has a non-linear angular velocity through a 360 degree rotation. Since both ends of the propshaft experience this (cos they both have a UJ in), and the variation in angular velocity depends on the deflection angle through the UJ, if the two ends have different angles of deflection they will be trying to turn with different velocities...

I *think* that's right!?! :huh:

If you don't want to change shafts, but need to get rid of the vibration, the only way is to reduce the difference in the angles of the planes of the flanges (to zero preferably).

If anyone spots anything wrong in the above, please let me know! :)

Al.



you've used *think* instead of speech marks "think"
;)
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#13 Turbocharger

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Posted 05 October 2005 - 07:14 PM

castor correction arms make the problem worse BTW


But don't castor-correcting arms/bushes rotate the axle so the flanges are more parallel?

As I understand it you can enter the weird weird world of mathematics and find an offset so the UJs aren't aligned on the shaft but will run balanced with a Z-angle discrepancy - I think the problem here is that the angle is too great, period.
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#14 D9OSV

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Posted 05 October 2005 - 07:42 PM

You are all pretty close.....

I will try to explain as simply as I can.....

White 90's picture shows the problem perfectly

Wot is happening is that (Astro al is spot on here) Is when a propshaft is used in anyother plain other than striaght, it turns going fast slow, fast slow fast slow

Under stand???????

Let me try putting it differently if you look at white 90's picture you will see that the uj nearest the diff is inline with the prop, So when this is rotated it travels as a consant.

However the uj at the other end of the propshaftis working at a greater angle (nearly20' i guess) This means when it turns t goes fast slow fast slow fast slow causing an ossilation.

Before the new springs where fitted the propshaft angles would have been much closer, thus when the propshaft turned the action of each uj cancelled out that of the other......Yeh, got it
This why when you fit a carden jointed(triple jointed) Prop the problem is solved.

This is because the double joint cancels itsself out and the lower is turning inline, therefore no Viberation.

Bloody Hell, do hope that wasn't to complicated to understand

If in doubt call me ;)


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#15 white90

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Posted 05 October 2005 - 09:23 PM

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the fix
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#16 Budgie

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Posted 05 October 2005 - 11:03 PM

But don't castor-correcting arms/bushes rotate the axle so the flanges are more parallel?

Not really, they rotate the axle to bring the caster angle on the steering back into the normal position.
This action lowers the diff flange, increasing the angle on the U/J on the transfer box end of the propshaft.

I had the same on the Disco when I corrected the caster angle. It set up a low speed Pulsing on the front prop and was only fixed with the Cardon front prop off a TD5 Disco. If you leave it too long before doing anything then it will first start leaking from the transfer box output seal and, in time, will wreck the output bearing as well!
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#17 BogMonster

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Posted 06 October 2005 - 12:23 AM

a disco S2 front double CV shaft! thats what you want Stephen!



Oh no it isn't!

They are 450 odd and the one on my Discovery is on the way out at 25000 miles of almost all on-road use, I know of several others that have failed - you can't grease the double-cardan joint and the ball joint thingy between the two UJ's develops play and eventually the shaft has to be dumped as you can't replace that bit, only the UJs. Probably not an issue on surfaced roads but it is here... the common fix on a Td5 Discovery is to fit a normal 300Tdi front prop which is the same length (or near enough) and 1/3 the price, nobody has yet commented on any vibration problems. Not sure what I am going to do on my Discovery as the V8 one is different :angry: one thing for sure is I ain't forking out that sort of money for a new one!

I think I might take out the spring isolators and see if the 1/3" drop is enough to get rid of the problem, if not then I will have to think again :(

I must go and look at my old red 90 and measure the spring thickness on that, to confirm they were 90 rears, as that was OK (but didn't have the isolators IIRC) maybe if I took the older rear springs and put them on the front without the isolators that would be the answer.

I just hate taking front shockers off, the bottom nuts are always a PITA. They must have a special gadget in the factory for doing them, either that or they just give the job to somebody they really dislike :lol:
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#18 white90

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Posted 06 October 2005 - 10:56 AM

They are 450 odd and the one on my Discovery is on the way out at 25000 miles of almost all on-road use, I know of several others that have failed - you can't grease the double-cardan joint and the ball joint thingy between the two UJ's develops play and eventually the shaft has to be dumped as you can't replace that bit, only the UJs. Probably not an issue on surfaced roads but it is here... the common fix on a Td5 Discovery is to fit a normal 300Tdi front prop which is the same length (or near enough) and 1/3 the price, nobody has yet commented on any vibration problems. Not sure what I am going to do on my Discovery as the V8 one is different :angry: one thing for sure is I ain't forking out that sort of money for a new one!


Steve I could post you one far cheapear than that!
and Jim AKA D90SV does a mod on them replacing the non greasable joint for one that can be serviced
for a very reasonable price. when my one needs replacing I'll be posting mine to him for attention.
Alternativley you can buy a double carden joint from the USA and fit it o your current prop.

prop info

Posted Image

I would replace it as your vibes will:
annoy
waste money trying to cure
only be fixed properly once the prop issue is sorted IMHO
Tony


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#19 dollythelw

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Posted 06 October 2005 - 11:04 AM

Burgess of bradford are a good place for double cardans, just specify landrover joints and its easy a pie to service after that
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#20 Bush65

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Posted 06 October 2005 - 11:54 AM

Much of what has been said above about u-joint, drive flange angles is not correct for coil sprung rover front drive shafts.

The usual practice for driveshafts, but not for rover fronts, is:

When a u-joint connecting 2 non-parallel shafts (t/case output shaft and driveshaft, or drive shaft and pinion shaft) rotates, the rotational speed of both shafts differ during each revolution. I think Astor Al explained this.

If the t/case output shaft rotates at a uniform speed, the driveshaft will speed up and slow down 4 times every revolution of the t/case output shaft.

If the diff pinion and the t/case output shaft are parallel, ie. both u-joints operate at the same as the angle, the diff pinion will also speed up and slow down 4 times every revolution of the drive shaft.

Now if the yokes at both ends of the drive shaft are in line, as the drive shaft speeds up, the diff pinion slows down, and as the drive shaft slows down, the diff pinion speeds up. So both the t/case output shaft and the diff pinion rotate at uniform speed. They are said to be in phase.

A double cardan joint consists of 2 close coupled u-joints with a centreing ball joint that ensures they are in phase. So if the t/case output shaft and the drive shaft rotate at uniform speed.

When a double cardan joint driveshaft is used, the diff pinion shaft has to be inline with the drive shaft, or else the diff pinion shaft will speed up and slow down and cause a vibration.

Getting back to coil sprung rover front drive shafts (excluding those with double cardan joints).

Because of the radius arm front suspension, the diff pinion shaft angle changes as the axle droops. The t/case output shaft and the diff pinion shaft can not be parallel, though the range of suspension travel.

These shafts are out of phase and vibration will occur. But rover have a cheaper solution than using a double cardan joint. What they do is rotate the yokes at both ends of the driveshaft out of line. So that the out of phase due to the deliberate miss-alignment of the yokes, approximately cancells out the out of phase due to the non-parallel shafts. You can clearly see this in the photo in White90's 1st reply at the top of this thread.

If you align the diff pinion shaft parallel with the t/case output shaft as was suggested, then you will get a severe vibration because the yokes at both ends of the driveshaft are not inline.

Of course, you can align the yokes in the driveshaft, but you have the problem that the radius arms change the angle of the diff pinion as the axle articulates.

IMHO, the best solution with suspension lift is to correct the angle of the diff pinion by cranking the radius arms, then correct the castor angle by rotating the swivel housings.

But the diff pinion must not be parallel with the t/case output shaft as was suggested by someone else here.

With a double cardan joint driveshaft the diff pinion should be parallel with the drive shaft.

Trial and error is required (depends on how much the suspension is lifted) to get the pinion angle correct for the rover driveshaft with out of line yokes. The other thing to try with these drive shafts, is to rotate the slip joint yoke one spline to see if out of phase of the driveshaft cancells the out of phase of the t/case output shaft and the diff pinion.

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