Any ideas? The car was in for a service and a few bits last week and had the rear diff pinion seal replaced as it had failed and sprayed oil everywhere. On replacement, there is now a whine from somewhere, increasing with speed. It's not roadnoise or gear box - any ideas, and will it be (very) expensive? It wasn't doing it before it went into the garage, but unfortunately, they're 150 miles away, otherwise I'd be back there...
O
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Jaguar XJS V12 - comes with free personalised oil tanker.
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To replace the pinion seal the pinion has to come off. Unfortunately that is the cause of your problem. IIRC on these diffs the pinion bearing pre-load is set with a crushable spacer which collapses down as the pinion is tightened up. This is a 'one time' process. In undoing the pinion to replace the seal you have lost the correct pre-load and the pinion bearing is whining. You have probably also changed the pinion-crownwheel backlash so the tooth contact pattern is different to what it should be and that will be making a noise too.
Really, the solution is going to be a re-con diff. Or back to the garage and ask them to strip the diff and replace the pinion bearing and use a new crushable spacer etc. I have done this on Merc diffs in the past - I've charged about £350 (the pinion bearing kit is about £70 on the MB's and the rest is labour - a few years ago now, mind). I suspect you would be looking at this kind of a figure for the Jag.
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I think it is also true to say that you should act quickly, or the gear pair will begin to wear in its new, incorrect, relative configuration, and even if the pinion pre-load is reset, the whine will not go away.
number_cruncher
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To be honest, if you take the pinion out and re-set the pre-load it may still whine a little. The teeth will not be in *quite* the same position at they originally were and so will make a little bit of noise. After 10-20k miles it will probably go away as the teeth polish into their new contact position.
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Oil seals do fail for no apparent reason, but it's usually a slow process rectified in the short term by topping up. A sudden failure often means that a nearby bearing has failed, allowing more movement between the seal and the sealing surface.
I can't say I've ever done a Jag pinion seal, but I've done a few others and never yet had to remove a pinion to replace the seal. In fact I've never been able to, as the pinion is always far too big to be withdrawn through the inner bearing.
I don't know how your garage did the job, but normal practice is to remove prop shaft and diff drive flange, lever out seal and replace in reverse order. The flange securing nut is usually nipped up fairly tightly - but not enough to collapse the crushable spacer any further. This usually puts things back as they were. A better way is to remove flange, seal and outer bearing - the collapsible distance piece can then be removed and replaced with a new one. The pinion securing nut is then tightened until the spacer collapses enough to give the required (worn) bearing preload. (established by reference to manufacturers spec. and usually by measuring drag when rotating pinion).
The advantage in method one is that it's quick, cheap, and usually works. Method two is a bit more expensive but it does allow the outer bearing to be inspected.
In either case an incorrectly tightened nut can cause a bearing whine (not diff) and must be sorted out fairly soon, unless, of course (back to paragraph one !)
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Don't disagree with the above, but I really am doubtful that you can get away with doing this job without replacing the crushable spacer tube. I don't see how you get back to the correct pre-load by using an already crushed tube in there - it won't be *quite* right. I suspect the pre-load (and associated drag torque) given in the manuals would be for a new bearing set anyway. I guess the way to do it would be to measure the drag torque before renewing the seal and set it back to that value using a new crush tube.
I'm not familiar with the Jag diff., but I've done a fair number of MB diffs in the past and found that once the pre-load comes off the pinion bearings things seem to 'move' a bit and the even when you put in a new spacer tube and torque the nut to get the correct pre-load the crownwheel-pinion backlash has altered a tiny bit. I have confirmed this by using 'blue' on the teeth and noted that the contact pattern has changed a bit.
At the MB factory they use a special piece of machinery (made in Japan!) which "listens" to each crownwheel-pinion pair and moves the pinion until the gear mesh becomes 'quiet' - this is then the setting for that pair and they are marked up as such. MB diffs are very picky and I have driven many a Merc with diff whine.
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Don't disagree with the above, but I really am doubtful that you can get away with doing this job without replacing the crushable spacer tube. I don't see how you get back to the correct pre-load by using an already crushed tube in there - it won't be *quite* right.
A method I've read about is to mark the nut position in relation to the shaft, then count the turns to remove it. Re-start it from the same point on the threads, and re-tighten to exactly the same position. It sounds good in theory, but in practice it is always very difficult to "catch" the nut at just the moment when it disengages from the threads.
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Orson,
I'm summarising from an article entitled "XJS V12 owner's guide" in this month's (June '05) edition of Jaguar World Monthly www.jaguar-world.com/ (Playjag as my little nest of vipers calls it), so I hope they don't mind a little advertising.
Pre HE cars were fitted with either a 3.31 or 3.07 LSD Salisbury diff. HE models came with a 2.88 Salisbury or Dana LSD. The Dana diff can be recognised by absence of a drain plug. Dana will still rebuild diffs and can be contacted on 0121 249 2649.
"These diffs are usually long-lived, with the exception of the pinion seals (which require care to replace in-situ).."
No personal association with the mag, but I can recommend it for Jag owners. Available at WHS for £3.95 or subscribe online.
Kevin...
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Thanks all for this - I'm getting it into my local for him to have a look and see - if it is a recon diff, then fitted, it's getting on for £900 - about 8 hours labour the guy reckons. The local garage can have a look and tell me what it is, as the specialist is a way away. he said it might be a wheel bearing, but I understood them to be more of a rumble than the whine that is present. Might have a word about getting a bit knocked off, seeing as it was fine when it went in, and he cerainly didn't say "if you have this done, then it could cock everything else up as well"
I'll see what happens...
O
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Jaguar XJS V12 - comes with free personalised oil tanker.
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Just back from Derek Watson Jags of Bakewell (top chap and great advice) who diagnosed the crushed spacer and knackered diff due to it being tightened up too much when the seal was done. He even got on the phone to the guy who did it and suggested that he might like to fix his mistake for nothing, which he has, to his credit, agreed to do gracefully. So there - a good news story!
Thanks for all your advice.
O
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Jaguar XJS V12 - comes with free personalised oil tanker.
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Glad its worked out. To be fair its not easy to tighten back correctly and guarantee the job. I wouldn't want to do it.
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I'll second that. It is very easy to make a quiet crown wheel and pinion drive noisy. It would have to be a serious leak on a car of mine before I would be tempted to undo the pinion nut to fit a new seal!
Having never given this much thought before, what is the *exact* purpose of the collapsible spacer?
If the spacer were designed to act as a significant loadpath, then it wouldn't be collapsible, it would just be a cheaper cylindrical tube.
If the spacer were not in place at all, one could still tighten the pinion nut gradually, feeling the resistance from increase as the bearing pre-load increases, and lock the pinion nut once the drag torque is correct. As the taper roller bearings are back to back, the inner races will not come any closer together even without the presence of the spacer.
The position of the pinion is governed by the shims between the back of the pinion and the inner race of the inner bearing - I can't see how the spacer changes it.
Am I missing something obvious?
number_cruncher
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The spacer determines the preload on the pinion bearings - nothing else. Other settings ( Mesh etc.) are usually determined by fixed methods - shims and solid distance pieces etc. It takes maybe 100 ft/lbs to crush a collapsible spacer, so in effect the pinion nut is fully tightened against an 'adjust as you go' shim, taking the taper bearings along with it. The outer bearing tracks stay in the same place, hence the preload.
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The collapsable spacer tube sits between the inner of the front bearing and (usually) a collar on the pinion shaft - it basically gives you something to 'tighten against' to set the preload. The mesh does change a bit with preload (at least on Merc diffs) probably because as you apply pre-load the taper rollers are pulled tighter into the outer tracks and there is some physical movement. The mesh is, however, mostly determined by so-called 'compensating washers' that sit between the rear bearing and the housing. On Mercs they are about 1mm thick and you can buy them in 0.05mm increments. Mercs diffs are a bit twitchy on pinion bearing pre-load and the wrong amount will cause diff gear whine (mind you, the backlash between crownwheel and pinion on a Merc is only about 3thou).
You can tell whether you have gear whine or bearing whine. Bearing whine tends to be there from low speed all the way up and doesn't vary much as you ease on and off the pedal. Gear whine is at tooth contact frequency and is most prominent around 60-70mph (about 2000 Hertz). You can 'play' diff gear whine on the throttle and its sometimes more prominent on the overrun when the 'rear' sides of the teeth touch. On Mercs renewing a pinion seal will often lead to some gear whine on overrun at about 60mph because the preload ends up wrong and the mesh just changes enough to cause a noise. Some W124/W102/W202 can be really bad, howling as you ease off the throttle from anything over 30mph, it can really spoil a car. When you think about a hypoid diff its amazing they're ever quiet at all!
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I agree broadly with the points you have given, none, and when counting the number of crownwheel and pinion sets I have overhauled, I don't run out of fingers! But, I think there is a little more to it.
You could build up a pinion without a spacer. You would have the right shims behind the pinion gear, getting the pinion depth right, and you could tighten the pinion nut to get the right preload. Lets say that the pinion nut has torque, T ft/lbs on it at this point.
Now if you were to build up a similar pinion using a spacer as specified, you would end up with the pinion at the right depth, and the bearings at the right level of preload, but, you would have more than T ft/lbs on the pinion nut.
The torque on the pinion nut is the obvious difference.
The loadpath from the pinion flange via the inner races, outer races and diff housing is completely unchanged, as the bearing preload is unchanged. But, the load pulling the pinion against its positioning shims and bearing inner race is much higher because of the higher torque on the pinion nut.
I think the collapsible spacer allows you to hold the pinion in position with more force, and stiffness, without applying this extra force to the bearing preload - i.e., it protects the bearings against excessive preload.
number_cruncher
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I think the collapsible spacer allows you to hold the pinion in position with more force, and stiffness, without applying this extra force to the bearing preload - i.e., it protects the bearings against excessive preload. number_cruncher
Yes, well put, that is what I was trying to say in my post above when I wrote that it gives you something to 'tighten against' - not very good English, but essentially what I meant was that it enables you to have a much higher 'clamping force' than if it wasn't there. In fact when setting up the diff gears and setting the backlash I have assembled and pre-loaded the diff without the spacer. Then, when it is all correct and I have the correct thickness compensating washer I would put the spacer in and tighten it all up.
Its five years since I last did a diff rebuild and I'm not anxious to do one again.
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Thank you all for your responses on the issue of the purpose of the collapsible spacer. You have helped me to clear up my thinking about it. My previous understanding was hazy, to say the least.
number_cruncher
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