XJR 97 shaking/juddering steering and braking

[nitramshirley]

74,000 miles, '97 XJR. The steering shudders quite perceptibly and consistently on marginaly bumpy road surfaces. At first I thought this was just due to the large wheel surfaces and taught ride, but now I am convinced it is either a shock-absorber problem, or a steering flaw. I have read elsewhere that the shuddering - which seems more severe when I brake - may be caused by faulty brake calipers. I have pretty new tyres and have balanced the wheels recently... so I don't think that those are the cause. Any suggestions before I take her to a dealer?

[GavinPearson]

nitramshirley said:

74,000 miles, '97 XJR. The steering shudders quite perceptibly and consistently on marginaly bumpy road surfaces. At first I thought this was just due to the large wheel surfaces and taught ride, but now I am convinced it is either a shock-absorber problem, or a steering flaw. I have read elsewhere that the shuddering - which seems more severe when I brake - may be caused by faulty brake calipers. I have pretty new tyres and have balanced the wheels recently... so I don't think that those are the cause. Any suggestions before I take her to a dealer?

At a guess I would say the tyre vibration is a tyre quality issue. Take the car to a Jag dealer and get the tyres checked on the Hunter 9700 for force variation.

With respect to the brake judder the discs are warped because the wheels have been incorrectly tightened. If torque varies the disc gets cocked which wears flats on it leading to judder. The way to diagnose is to remove the wheel, clamp the disc evenly and measure run out. This will determine if the discs need replacing. I doubt very much that it is calipers.