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Gearbox/Transfer box question


Ivan
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Mods please don't put this in the Disco forum as I am suer it applies to other vehicles.

I have a Discovery with a 2" lift and castor corrected radius arms (Gwyn Lewis). Myproblem is, if you accelerate to 70mph and then come of the throttle you get a horrible graunching noise from the gbox/txbox until the speed drops. I have been told this is caused by "propshaft flutter" caused by the lift. So I fitted a new high angle propshaft (Gwyn Lewis again) and it still makes the noise. I have checked the input gear in the txbox and it's fine (Ashcroft Q gears) and there is no wear on the splines from the gearbox. It has only been doing this for about 6/7 months. Prior to this there was a slight noise but nothing like the noise I am getting. It sounds like either bearings that are failing or gears that are not meshing correctly. I have asked Ashcrofts and they could not come up with a reply. So, any clues ?

Rgds

Ivan

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you say ashcrofts didnt reply, did u actually call them and speak to them? or just email? I'd imagine a gearbox specialist would have heard of these symptoms before and give at least some idea of where to look...

try calling bernie at Competition Transmission Services to see if he has any ideas 01582 840008

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I just emailed Ashcrofts and it didn't reach a conclusion. It's definitely not the diffs. These have just been rebuilt with 4.11 R&P's from Ashcrofts. If I take the front propshaft the noise stops, but you get an awful lot of backlash in the txbox then.

Thnx

Ivan

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Looking at Gywn's website, I'd say your 'high angle' prop is the likely suspect. While it may offer more flexibility off-road, it's still got two conventional UJ's at either end. What you want is a Double Cardan prop from a Discovery 2 that's better able to cope with the steeper running angle.

Vibes on Disco's post lift are commonplace and almost gauranteed. I had a similar bad vibration on my lifted Disco on a trailing throttle (overrun). This was cured instantly when I fitted a D2 front prop with the Double Cardan joint.

You'll also need replace to the output flange on the T-Case with one from a D2, but other than this small mod, the two shafts are a straight swap. Price for a shaft and flange is approx £200. You may find a secondhand one, but be aware the standard LR item has no grease nipples fitted. I think D4x4 are now selling greasable versions.

Kev

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The backlash you mention could be the cause, with the high angle of the prop UJ's this could send vibes back up the train, and where it finds a load of slack things will start clanking around. My truck made lots of clunking and banging until I changed the (worn out) input gear for a new one.

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Mods please don't put this in the Disco forum as I am suer it applies to other vehicles.

I have a Discovery with a 2" lift and castor corrected radius arms (Gwyn Lewis). Myproblem is, if you accelerate to 70mph and then come of the throttle you get a horrible graunching noise from the gbox/txbox until the speed drops. I have been told this is caused by "propshaft flutter" caused by the lift. So I fitted a new high angle propshaft (Gwyn Lewis again) and it still makes the noise. I have checked the input gear in the txbox and it's fine (Ashcroft Q gears) and there is no wear on the splines from the gearbox. It has only been doing this for about 6/7 months. Prior to this there was a slight noise but nothing like the noise I am getting. It sounds like either bearings that are failing or gears that are not meshing correctly. I have asked Ashcrofts and they could not come up with a reply. So, any clues ?

Rgds

Ivan

Hi Ivan,

I did reply, I just didn't have the answer !

I agree it's lift / front prop related,

bit more reading here :

prop vibrations

when the prop turns it accelerates and decelerates, the bigger the flange angles the bigger the speed variation on each Rev,

the high angle prop will stop the UJ bottoming out but will do little to cure the vibrations,

have you considered trying a disco II 'double cardan' front prop, I think these are designed to address the 'speed' fluctuation and thus the vibrations,

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I am paying interest in this posting as i have the same symptons on my defender with a big lift ,it seems that we are trying to get a steep angled prop to run like standard ,it would be nice if we could i would love to get rid of my vibs ,Does a double cardan prop make it even steeper with that extra joint if it works i will buy one tomorrow

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After I had to sort out some vibration issues on a propshaft driven fire pump at work (F**king massive shaft, yokes were 7" across) and spending a worth while 1/2 hour on the phone to the propshaft clinic discussing props for my 90 I found quite a bit out about this.

For good background reading try looking in the tech section of Pirate 4x4.com. At the bottom of the page is a long write up of the theroy of propshafts. It explains why you get vibration, why you would want a double cardan shaft etc.

For those not wanting to wade through 5 pages of tech on pirate4x4:

to prevent vibration a simple prop shaft must have the same angle in the joint at each end, and the angles must be in the same plain. Eg the rear prop shaft in a 90. Both the transfer box and diff are horizontal. As the transfer box output shaft and diff pinion also line up this means that the angle at each joint in the propshaft is identical and in the same plain. Therefore if the yokes are set out of phase by 90 degrees then the acceleration/deceleration effect you get in each joint it canceled out by the joint at the other end of the shaft doing the opposite. This results in no drive shaft vibration and a happy driver.

When you come to the front of a land rover the diff points (sort of) at the transfer box and the joint at the transfer box has all the 'bend ' in it. This means that the angles in the two joints are not equal. This does not comply with accepted propshaft design practise. To 'fix' the issue LR found the optimum angle between the yokes at either end of the prop that minimises the vibration.

Then we come allong and lift the motor. This alters the angles at the rear of the vehicle by an equal amount at either end. As long as the joints do not bind at the rear, the rear shaft is OK.

However at the front the LR compromise is not valid as we have changed the angles in the joints at both ends by different amounts. To compound this we then stick 'castor corrected' radius arms on the vehicle. This points the diff downwards and messes up the situation even more.

From my understanding of the problem the solution is one of the following. Note that both require the use of standard radius arms (which are stronger any way):

a/. Revert back to standard radius arms to get diff pointing as close as possible to transfer box. Then repeat what LR did - test the level of vibration with the propshaft assembled in every combination of yoke offset allowed by the splines. You may find one that gives an acceptable level of vibration.

b/. Used standard radius arms to point diff at the transfer box. Then fit a double cardan shaft. This has 3 joints in it. The double joint at the transferbox are offset by 90 degrees to each other. This means they offset the acceleration/deceleration effect that each produces. Then as long as the joint at the diff end of the shaft has NO bend in it the shaft will not vibrate.

The only issue with these solutions is the lack of camber correction. I fitted camber corrected swivels (from Tomcar motorsport) on my 90 and they work well and because I have standard radius arms I do not get propshaft vibration.....

Some other interesting facts I found out:

To get good life out of a joint it must run at an angle to ensure that the rollers in the joint move. Otherwise freash grease doesn't get under the rollers and eventually you get a joint failure due to lack of lubrication (even if you pump loads of grease in).

Beyond a certain angle (roughly a couple of degrees) the life expectancy of a joint decreases significantly. Therefore when you lift you motor the joints will wear out more frequently (the bloke at the propshaft clinic was getting fed up at this point so I never found out what the mechanism of this is - maybe something to do with the amount of roll required by the little rollers in the joints? - the more movement(read angle in joint) required the faster they must roll).

Apparently a cetain supplier of 'orange' products sell a wide angle joint. This allegedly uses joints from muck spreaders. They are still only designed to transmit power at low angles - the wide angle bit is to allow the farmer to turn (with the power off) at the end of the field. So if we use these to resolve propshaft issues on a vehicle with big lift we are using tham at angle that they were not designed to operate at. Hence thay wear out joints on a regular basis (so I was told) if used at larger than normal angles.

Anyone spot any mistakes in the above feel free to point out as I have been at the cider....

Adrian

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Obviously you're not making this up or imagining it, but I am surprised as I just did a 2" lift, without castor corrected arms - which you ought not really need with only a 2" lift (perhaps as per Bill's point above). I have other noise and issues (surprise), but not prop vibration. Have you oiked about with that rather bizarre harmonic damper thinggie ? Seems to me that this was a pretty clever LR bodge. "Front prop is vibration prone anyway, so let's pop this vibration damper on it". Can't say what you would do with it exactly, but I would hit it with a hammer a few times as a minimum, or possibly make sure it's functioning as intended...

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Sorry Dave I should have worded it better. I did not mean that you were unhelpful just that you could not provide the answer.

RPR I binned the harmonic damper years ago without any apparant ill effects.

I'll talk to Gwyn about it and see what we come up with. I did try and get a double cardon propshaft but as I was going on holiday and they didn't have one I settled for the high angle.

Rgds

Ivan

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Obviously you're not making this up or imagining it, but I am surprised as I just did a 2" lift, without castor corrected arms - which you ought not really need with only a 2" lift (perhaps as per Bill's point above). I have other noise and issues (surprise), but not prop vibration. Have you oiked about with that rather bizarre harmonic damper thinggie ? Seems to me that this was a pretty clever LR bodge. "Front prop is vibration prone anyway, so let's pop this vibration damper on it". Can't say what you would do with it exactly, but I would hit it with a hammer a few times as a minimum, or possibly make sure it's functioning as intended...

You are right that the lift on its own normally causes little problems vibration wise. It is when it is combined with castor correction that the prop complains.

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