Strange noise/vibration from XK8
Discussion
Any ideas would be welcome in relation to a problem I have with my 2003 XK8. Basically on a constant throttle at around 70mph I get a vibration through it that feels like something, probably at the rear, is binding a little. It certainly doesn't feel like a wheel out of balance type vibration but I do also get that sensation if accelerating gently at around 50mph. The 70mph vibration goes if I shift the gearlever to 5 or accelerate and the car feels fine at 80mph plus (on private roads of course). Simiilarly, harder acceleration at 50 and the vibration isn't there.
I initially wondered if it was a brake binding as I recently fitted new discs, shoes and pads at the rear and the n/s was binding slightly after that but have now sorted that and the vibration is still there. It certainly seems to be worse when it is fully warm. I am wondering if it might be a wheel bearing, but they are fairly new and not making noise under other conditions, but it does have the wheel bearing failing type feel to it. Otherwise I guess I need to start worrying about the diff or gearbox
What can I look for?
I initially wondered if it was a brake binding as I recently fitted new discs, shoes and pads at the rear and the n/s was binding slightly after that but have now sorted that and the vibration is still there. It certainly seems to be worse when it is fully warm. I am wondering if it might be a wheel bearing, but they are fairly new and not making noise under other conditions, but it does have the wheel bearing failing type feel to it. Otherwise I guess I need to start worrying about the diff or gearbox
What can I look for?
My XJR has a nasty vibration at around 1800RPM even if its sat on the drive. Check the RPM when you get the vibration driving then when stopped rev in neutral to the same level , then try 100 RPM either side. If you get the vibration you can eliminate the Diff , driveshaft and wheel balance.
In my case apparently its 'within tolerance' for an XJR to vibrate its tits off at 1600RMP and make a thrumming noise with it. I think a jag should be a smooth wafty cruiser but Jaguar disagree and think that vibration sufficient to rattle my teeth is perfectly normal.
In my case apparently its 'within tolerance' for an XJR to vibrate its tits off at 1600RMP and make a thrumming noise with it. I think a jag should be a smooth wafty cruiser but Jaguar disagree and think that vibration sufficient to rattle my teeth is perfectly normal.
andyps said:
Thanks Steve, I agree, but it doesn't seem to do it at any other speed in other gears which is part of what I can't figure. I wondered if it is partly a torque based reaction which is why it goes away in a different gear.
Yes it could be and chances are it'll be a PITA to find.First establish as much information as you can. Don't assume you know what the cause is, try to prove it. As you suspect torque/engine then establish the precise RPM it occurs at. Does it do it all the time or more/less on/off load? First have a look for the bleedin' obvious like slack pulleys or missing bolts or broken heatshields. Standing at the side of the car run the engine at that critical RPM in Neutral and feel all over the block and ancillaries for any vibration. Under the car feel - with gloves on obviously - all along the exhaust at the same RPM. Carefully check all the exhaust mounts to make sure they've not ovalled or worn. Have somebody hold the critical RPM and repeat all the above with a slight rise and fall of RPM.
For what you describe the gearbox mounting could be a prime suspect, make sure all the bolts are tight.
There is some free movement so that doesn't sound right. I also noticed that the n/s rear wheel bearing is noisy when rotating the wheel - almost a knocking noise presumably as the rollers go around - and has more play than it should so I will get that sorted and hopefully it might be the issue. Is the gearbox mount a complex replacement? Thanks again for your help.
The only way to be absolutely certain is by direct comparison with a known good one. Unlikely you'll have the opportunity to do that so all you can do is replace it to see if that's the problem. It may be or it may not.
Broadly I'd do this.
First spend a lot of time and no money on analysis and research. Live with it, drive it and probe it and think about it. At the same time resist the temptation to stop in the next layby and just set fire to the poxy thing. Once you have a few hypotheses then cost them up for repair and replacement in order of priority. Balance those costs in terms of time money and hassle to yourself against a couple of hours at a known good independent for some fault finding.
He may find a weak exhaust mount that'll cost a tenner to replace or he may say, yup they all do that.
Broadly I'd do this.
First spend a lot of time and no money on analysis and research. Live with it, drive it and probe it and think about it. At the same time resist the temptation to stop in the next layby and just set fire to the poxy thing. Once you have a few hypotheses then cost them up for repair and replacement in order of priority. Balance those costs in terms of time money and hassle to yourself against a couple of hours at a known good independent for some fault finding.
He may find a weak exhaust mount that'll cost a tenner to replace or he may say, yup they all do that.
I had very similar symptoms on my Jeep Grand Cherokee (Yes I know it's not the same car) and that was fixed with a new rear gearbox mount. I think the old one had gone soft and was not only allowing the back of the gearbox to sit a touch lower it would be moving around more. Anyway, new rubber mount, job done and not too expensive to try.
I hope that helps for what it's worth
I hope that helps for what it's worth
A quick update - I picked the car up from the garage this morning having left it with them last week while I went to Le Mans for the classic race - they have replaced the complete rear hub on the nearside as it had wear on the inner bearing carrier through the bearing spinning on it and also they think the alloy had probably deformed slightly between the outer bearings meaning that they would not close up enough with a spacer between them. I haven't driven it enough to know if it has solved the issue yet but should do later today - I'll get back with another update once I have.
A couple of X350s I've driven have had traces of propshaft vibration. This presents as a much higher frequency than wheel vibration and is higher than a washing machine on a high speed spin whereas wheel vibration is a lot lower.
Make sure all the driveline bolts are tight and providing you're happy there's nothing wrong with the driveline, mountings, shocks or buses then try jacking the rear wheels off the ground - securely obviously - and run the engine up to vibration speed in Neutral first. Anything? Yes? It's a engine issue.
No? Then turn the traction control off and do the same this time in Drive letting the wheels spin . Feel it now? Take the wheels off and do it again. Better? Probably will be. Swap wheels front to back and try again. You will always get some wheel vibration when running up unloaded and the purpose of this is to familiarise yourself with the frequency of it as well as identify if any particular wheels are worse than any other.
Next take the wheels off again and put a Jubilee clip round the propshaft as far towards the rear as you can get it to deliberately throw the prop off balance.
Run it up again. The vibration may probably be worse, maybe quite a lot worse but the vibration frequency will be very different to that of the wheels. If this is the vibration frequency you experience on the road then either prop balance or worn UJs are your issue.
You could take the prop off and check all the UJ's for free play but before you do try this.
Mark the initial position of the clip as a reference and then move it round 120 deg. Run up again. Better/worse? Keep experimenting with the position of the clip and keep notes of what you've done. If you have a prop balance issue sooner or later you'll find a sweet spot where the weight of the clip significantly reduces or if you're lucky completely cancels out the vibration. If you don't it'll remain uniformly worse no matter where the clip is positioned and in that case chances are you've now identified the UJs are worn. If you find a spot where vibration at it's smoothest but not completely cured then mark that spot and put another clip on the shaft beside the first one. Next progressively move both clips in increments of a few degrees away from that mark in opposite directions round the shaft and see if you can improve it further.
Put is all back then go for a drive. Clips on the propshaft are a proper Old School mechanics bodge but they can work and cost nothing. You'll probably get all sorts of warning lights and messages on the dash whilst testing but they'll clear once back on the road .
Make sure all the driveline bolts are tight and providing you're happy there's nothing wrong with the driveline, mountings, shocks or buses then try jacking the rear wheels off the ground - securely obviously - and run the engine up to vibration speed in Neutral first. Anything? Yes? It's a engine issue.
No? Then turn the traction control off and do the same this time in Drive letting the wheels spin . Feel it now? Take the wheels off and do it again. Better? Probably will be. Swap wheels front to back and try again. You will always get some wheel vibration when running up unloaded and the purpose of this is to familiarise yourself with the frequency of it as well as identify if any particular wheels are worse than any other.
Next take the wheels off again and put a Jubilee clip round the propshaft as far towards the rear as you can get it to deliberately throw the prop off balance.
Run it up again. The vibration may probably be worse, maybe quite a lot worse but the vibration frequency will be very different to that of the wheels. If this is the vibration frequency you experience on the road then either prop balance or worn UJs are your issue.
You could take the prop off and check all the UJ's for free play but before you do try this.
Mark the initial position of the clip as a reference and then move it round 120 deg. Run up again. Better/worse? Keep experimenting with the position of the clip and keep notes of what you've done. If you have a prop balance issue sooner or later you'll find a sweet spot where the weight of the clip significantly reduces or if you're lucky completely cancels out the vibration. If you don't it'll remain uniformly worse no matter where the clip is positioned and in that case chances are you've now identified the UJs are worn. If you find a spot where vibration at it's smoothest but not completely cured then mark that spot and put another clip on the shaft beside the first one. Next progressively move both clips in increments of a few degrees away from that mark in opposite directions round the shaft and see if you can improve it further.
Put is all back then go for a drive. Clips on the propshaft are a proper Old School mechanics bodge but they can work and cost nothing. You'll probably get all sorts of warning lights and messages on the dash whilst testing but they'll clear once back on the road .
Thanks again Steve. I did the jubilee trick many years ago on a Triumph Herald so will try again on the Jag - not massively happy at running it up to 70mph on axle stands though! It will be a while before I get chance to do anything however as I have a lot of other things on and the car may have to wait. I'll let you know though.
I finally found the issue (I hope) so thought I would update in this thread. It seems it was a torque converter issue and is reasonably common. I managed to pinpoint it through the use of an OBD reader connected to my phone which gave me lots of data but really showed the revs fluctuating considerably whilst driving at a steady pace - they were changing quicker than the rev counter would show.
Apparently there is a seal which goes on the torque converter and this causes the vibration and fluctuating engine noise. I got a secondhand box which was fitted today and the drive home was much more pleasant, just trying to ignore the dent in my bank balance!
Apparently there is a seal which goes on the torque converter and this causes the vibration and fluctuating engine noise. I got a secondhand box which was fitted today and the drive home was much more pleasant, just trying to ignore the dent in my bank balance!
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