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jarrod

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just bought a 1990 jag xjs v12 want to know if there is anything to watchfor. It has 90,000 miles and was running poor till I pushed the second coil wire back on. It has a slight vibration at high rpm's uv joints? just appreciate your input as this is the first high end car I've ever owned> Thanx in advance,
Jarrod
 
You have got to be more specific about the vibration. Where does it seem to be coming from and at what RPM or MPH? I might be able to help you with more specifics.
 
from 4,000 and above it doesn't do it all the time and is real slight. it comes fromthe mid to rear of the car
 
Since you are feeling/hearing it from the middle or rear and if it is in sync with the rear drive and not the engine which would come and go as you drove through the gears I think your vibration is originating from U joints in the drive shaft or the half shafts. U joints can fail by getting loose or by getting stiff around a needle bearing cup. In order to detect the stiff joint situation you will have to individually unhook the joints and work them through their range. Looseness can usually be detected by visual inspection with the U joint in place. There is yet another source for such a vibration. There is a carrier bearing near the center of the drive shaft that supports the shaft on the monocoque frame. The carrier bearing can cause a vibration if worn or may require "nulling" vibrations by shifting the carrier bearing slightly latterally. and retightening. This procedure is presented in the drive shaft section of the shop manual. I hope this discussion helps you sort out the problem.
 
It's also possible that the transmission mount is bad, allowing metal to metal contact. Get under the car and see how much you can move the rear of the transmission.
 
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