Check to make sure the handbrake works properly. If it doesn't, it can cost a lot to get it repaired because the handbrake calipers are above the diff, making them very difficult to get to, and the rear subframe / axle cradle has to be lowered to gain proper access.
Another thing to watch for is leaking fuel tanks and / or breather pipes. Because the tanks are in the rear wings, any leaks will have the interior of the car stinking of petrol instead of smelling of wood and leather. Another thing about the twin fuel tank system is that it has various electrically operated valves to make the petrol go where it's supposed to, and stop it ending up where it's not meant to be. One known fault on the series 3 is that if the nearside fuel return valve (located in the nearside rear wheelarch) fails in the open position, it will allow unused fuel from the injector rail to be pumped into the nearside tank, which eventually means it will be full, even if you never put fuel into it yourself. Once it's full, it will overflow and if you look under the centre of the rear of the car, you'll see it coming out of the overflow pipe just behind the diff. For this reason, Jaguar used to recommend that the nearside tank was used first to prevent this.
Check for rust round the bonnet hinges.
Central locking sometimes doesn't work on series 3s.
Make sure the hazard warning light switch works properly and isn't broken. Because of their shape, they are vulnerable to damage.
If, when you drive the car, you hear a noise that sounds like the rear axle is about to fall off, it's probably the gearbox mount. The back of the gearbox sits on a coil spring and there's a bush in the middle which can deteriorate. When it does, the spring can bottom out and make a frightening noise. A long term fix is to replace the not very long lasting bush with a short length of pipe lagging.
On the V12, make sure the idle speed is correct. It should idle at about 650 to 700 rpm. If it's significantly higher than this, it could be the auxiliary air valve (not to be confused with the auxiliary air device). The AEV is water temperature controlled and is on the nearside bank of cylinders at the rear of the engine.There's an idle speed adjustment screw on it. If it fails, the idle will be stuck at whatever it was at when the thing failed. A workaround until you can get a new one is to block off the vacuum pipe which goes from the nearside air filter box to the inlet manifold, and then manually set the idle on the throttle linkage stop screw on each bank of cylinders.
If the speedo isn't working then the cruise control and computer won't work either.
In the picture below with the axle cradle on the floor, you can just see part of the handbrake calipers (pic courtesy of google picture search)
It's really difficult but not quite impossible to take the handbrake calipers off to rebuild them and replace the pads. A mate of mine did it on my series 3 with the subframe in place, but we did have to take the rear exhaust silencers and over axle pipes off to gain access. It's not unheard of for people to cut holes in the boot floor which correspond with the holes in the top of the subframe to avoid having to drop the subframe to do this job.
I've heard you can retro fit outboard brakes as used on XJ40s and X300s, but I don't know if this is true.
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Click for full size image - http://imagehosting.rodsnsods.co.uk/6754d472c174f5ff.jpg
Another thing to watch for is leaking fuel tanks and / or breather pipes. Because the tanks are in the rear wings, any leaks will have the interior of the car stinking of petrol instead of smelling of wood and leather. Another thing about the twin fuel tank system is that it has various electrically operated valves to make the petrol go where it's supposed to, and stop it ending up where it's not meant to be. One known fault on the series 3 is that if the nearside fuel return valve (located in the nearside rear wheelarch) fails in the open position, it will allow unused fuel from the injector rail to be pumped into the nearside tank, which eventually means it will be full, even if you never put fuel into it yourself. Once it's full, it will overflow and if you look under the centre of the rear of the car, you'll see it coming out of the overflow pipe just behind the diff. For this reason, Jaguar used to recommend that the nearside tank was used first to prevent this.
Check for rust round the bonnet hinges.
Central locking sometimes doesn't work on series 3s.
Make sure the hazard warning light switch works properly and isn't broken. Because of their shape, they are vulnerable to damage.
If, when you drive the car, you hear a noise that sounds like the rear axle is about to fall off, it's probably the gearbox mount. The back of the gearbox sits on a coil spring and there's a bush in the middle which can deteriorate. When it does, the spring can bottom out and make a frightening noise. A long term fix is to replace the not very long lasting bush with a short length of pipe lagging.
On the V12, make sure the idle speed is correct. It should idle at about 650 to 700 rpm. If it's significantly higher than this, it could be the auxiliary air valve (not to be confused with the auxiliary air device). The AEV is water temperature controlled and is on the nearside bank of cylinders at the rear of the engine.There's an idle speed adjustment screw on it. If it fails, the idle will be stuck at whatever it was at when the thing failed. A workaround until you can get a new one is to block off the vacuum pipe which goes from the nearside air filter box to the inlet manifold, and then manually set the idle on the throttle linkage stop screw on each bank of cylinders.
If the speedo isn't working then the cruise control and computer won't work either.
In the picture below with the axle cradle on the floor, you can just see part of the handbrake calipers (pic courtesy of google picture search)
It's really difficult but not quite impossible to take the handbrake calipers off to rebuild them and replace the pads. A mate of mine did it on my series 3 with the subframe in place, but we did have to take the rear exhaust silencers and over axle pipes off to gain access. It's not unheard of for people to cut holes in the boot floor which correspond with the holes in the top of the subframe to avoid having to drop the subframe to do this job.
I've heard you can retro fit outboard brakes as used on XJ40s and X300s, but I don't know if this is true.
Click for full size image - http://imagehosting.rodsnsods.co.uk/6754d472c174f5ff.jpg
