I have a 4 litre 2001 XK8 convertible that has done 45000 miles and recently it has been making a noise between 40 and 50 mph. It happens under light load in top gear at a steady speed and sounds a bit like an exhaust resonance, although a Jaguar mechanic in the passenger seat did say it sounded a bit like a back axle whine. It quietens above and below this speed range.
After several attempts, including the use of microphones listening to critical spots on the underside my main agent is proposing to change the differential unit. My instinct is that the noise doesn't sound heavy enough for a unit in the main transmission train. Has anyone had a similar experience?
Steve
Resonance in transmission
Moderators:MarkX, mike020150
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mike020150
- Posts:3469
- Joined:Wed Feb 08, 2006 6:26 pm
Thanks for that Mike; exhaust was my first thought too and I expressed that fairly strongly to the garage. There has been some progress now though that members might like to hear about.
The garage did check the exhausts thoroughly and then used a gadget called Chassis Ears (Jaguar toy I think) that puts sensors everywhere on the chassis to help localise noises that are hard to trace. This pointed quite strongly to the differential so with some trepidation I agreed to have it changed. Two days, and a whopping bill, later it was returned and on the first run it was obvious nothing had improved so it was straight back to the garage with a pretty strong comment about them having failed to cure the problem. Full marks to Merrits of Amersham, they did the decent thing and absorbed their mistake and went on trying to find the problem. Chassis Ears was still pointing at the back axle, but the next theory was a bearing at the back of the gearbox, or possibly the box itself. They have returned the car to me today and so far (pending a longer workout tomorrow) all seems well. It is a fault the main agent has never seen before so may help guide diagnosis if it ever pops up elsewhere.
At the back of the gearbox there is a short shaft with a sort of spider on it that carries the drive to the front of the prop shaft. The rear of this short shaft is held in a bearing held in a mini bell housing behind the gearbox. The bearing is held in place by a large nut and it seems that this had worked loose and the bearing was vibrating on the shaft. The short shaft, nut and bearing have been replaced and subject to the test tomorrow all seems to be well.
The big plus is that the bill was only about half of what it would have been with the differential, but Merrits have put the original diff back in for me, absorbing the labour that was necessary. They have put a lot of effort into diagnosing this unusual problem and been very fair over charging for it. I don't think I can criticise them at all.
I'll update you again after the longer road test.
The garage did check the exhausts thoroughly and then used a gadget called Chassis Ears (Jaguar toy I think) that puts sensors everywhere on the chassis to help localise noises that are hard to trace. This pointed quite strongly to the differential so with some trepidation I agreed to have it changed. Two days, and a whopping bill, later it was returned and on the first run it was obvious nothing had improved so it was straight back to the garage with a pretty strong comment about them having failed to cure the problem. Full marks to Merrits of Amersham, they did the decent thing and absorbed their mistake and went on trying to find the problem. Chassis Ears was still pointing at the back axle, but the next theory was a bearing at the back of the gearbox, or possibly the box itself. They have returned the car to me today and so far (pending a longer workout tomorrow) all seems well. It is a fault the main agent has never seen before so may help guide diagnosis if it ever pops up elsewhere.
At the back of the gearbox there is a short shaft with a sort of spider on it that carries the drive to the front of the prop shaft. The rear of this short shaft is held in a bearing held in a mini bell housing behind the gearbox. The bearing is held in place by a large nut and it seems that this had worked loose and the bearing was vibrating on the shaft. The short shaft, nut and bearing have been replaced and subject to the test tomorrow all seems to be well.
The big plus is that the bill was only about half of what it would have been with the differential, but Merrits have put the original diff back in for me, absorbing the labour that was necessary. They have put a lot of effort into diagnosing this unusual problem and been very fair over charging for it. I don't think I can criticise them at all.
I'll update you again after the longer road test.
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mike020150
- Posts:3469
- Joined:Wed Feb 08, 2006 6:26 pm
Hi Mike, I gave it a good workout this weekend and it does seem we have hit the right spot. The transmission is back to being as silent as a Jaguar is supposed to be. From what the garage said it wasn't something that happens very often as they hadn't come across it before, however, it does show how noise can travel in a chassis and pop out in places other than the source. Each of the mechanics who sat in the car felt it was coming from behind the driver, and the 'Chassis Ears' device that Jaguar use, whilst clever, can obviously be fooled.
The design of the transmission at that point in the XK8 seems unusual in thet it has this extra short shaft at the rear of the gearbox and a separate bearing before it connectes to the prop shaft. At least all the parts are replaceable.
This is one to put on the shelf and hope we remember it when someone else has the same symptoms
The design of the transmission at that point in the XK8 seems unusual in thet it has this extra short shaft at the rear of the gearbox and a separate bearing before it connectes to the prop shaft. At least all the parts are replaceable.
This is one to put on the shelf and hope we remember it when someone else has the same symptoms
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