[xj] John's wobble


I think the consensus is correct- this symptom usually is down to warped discs (rotors), though not always at the front, be warned. However I get the feeling from your last posting that you are not yet convinced. Here is an easy test which is conclusive and does not involve swapping the rotors.

You need what is called a dial gauge. This is an instrument capable of measuring in 1/10,000ths of an inch and has a pointer needle on a dial- hence the name. The instrument is used on a jig which allows the user to position it firmly. They’re not that expensive to buy and are vital for serious engine tuning, but you could probably hire one/scrounge the use of one from a local specialist. (Any decent garage should be able to do this test for you if you lack the time/desire/whatever and don’t mind paying an hour or so’s labour.)

You set the gauge up so that the tip of the probe is in contact with the disc (having removed the road wheel and jacked up the car) and then zero the gauge- it’s really very very easy, not at all techie- and spin the hub, while watching the needle on the dial gauge. If the needle shows more than 1 or 2 thou (thousandths of an inch, we like real measures in this establishment) runout on either of an axle set of discs (ie front or rear) then you either need to replace both the discs or have both resurfaced by a machine shop, assuming that this will leave the disc over specificied minimum thickness. Please do both sides the same way, otherwise the brakes will almost certainly pull to one side. And by the way always fit new pads to new or resurfaced discs.

That attends to the matter of the warped disc. However your symptom can also be caused by localised corrosion of the discs. This usually happens when you leave your pride and joy laid up in the garage for a couple of months in winter or whatever and the pads very kindly seize to the discs and rust them. This sort of damage is very obvious to visual inspection- the affected area will be black and probably pitted, and the damage will be in the shape of a pad. The cure is the same. This, by the way, is why it’s a smart move to remove the pads from your calipers when you lay up your car.

If your baby passes both these tests, (sorry, I said there was one, but it’s very late at night), then you need to do some serious investigation of the running gear, starting with the front ball joints, through the track rod ends to the subframe and suspension bushes. It is possible that one of these components is close to failure and said failure at speed could be very nasty indeed.

Good luck and happy motoring