The XJ6 Sovereign (X358) that I bought late last year suffered from steering wheel judder. I was told it could be disc deposit from standing too long at the dealership, but it persisted into January despite me doing nearly 3000 miles since purchase. Looking at the discs they looked very new, being mostly unrusted and also looked like Jaguar or OEM as they were plated in the centre rather than being bare cast iron. So I was loath to replace them. So I did a bit of internet searching and found this site: -

Brake disc skimming and service centres | Skim My Discs

Using this website I found a local garage that had the equipment and yesterday took the car in for a front brake disc skim. I watched as the machine worked, and it was amazing to hear the cutter first cutting intermittently around the disc to true it up, with the cutting noise finally become constant as the distortion was removed. In fact, according to the machine operator, (also the owner of the garage), it only took off about 3 thou off the driver side, and less off the passenger side. Now the judder has completely gone. Price for the job - £45 plus our swingeing VAT £9. Not bad, I think.

The garage specialise in Mitsubishi Evo cars for both road and track and bought the machine because just swapping out discs is very expensive. I believe many Porsche dealers also have the equipment. The equipment is made by Pro-Cut in the USA !

 

While this may have stopped the juddering, it also shaved off 3 thou of expensive rotor material. The practice of 'disk skimming' is sometimes 'disk scamming' over here.

In 99% of cases the juddering is not a warped rotor, just embedded pad material. Such material can easily be removed with a Scotch Brite type disc and a hand held rotary tool. This does not remove any rotor material, just the deposits.

3M Roloc Brake Rotor Surface Conditioning Disc Starter Pack 1410

 

A good price for a good result.

What the machine achieves is parallel and clean friction surfaces
perfectly aligned with the plane of rotation. This alignment can
be done by shimming between hub and disc, but few shops will
do this as they are unfamiliar with the technique. The parallelism
of the surfaces and plane of rotation addresses both pedal pulsation
and pad knockback.

A further benefit is that the surfaces have been machined on a
seasoned disc which means that the variations in surfaces
arising from initial heating and cooling cycles of a new disc
are not a factor. The discs should feel good for a long time.
In my opinion a properly machined seasoned disc is superior
to a new disc.

On vehicle disc lathes are indeed mandatory equipment for many
vehicle franchises including Jaguar. There are factory tsb's out
there mandating that the first step in addressing customer
complaints of brake pulsation be skimming the discs with such
equipment prior to replacement.

 

Well, I hear what you say, but the result speaks for itself. I'm happy and the disc still has plenty of life in it.

 

There's no doubt that the procedure is effective but it's kind of like saying that a sledgehammer is the minimum required tooling to squash a bug.

When disk brakes first became common place in '60s, they were produced with plenty of extra 'meat' on them, with the intention that they could be skim cut several times before falling below minimum acceptable thickness. This thinking was a follow-on from the drum brake days when cutting drums was common practice to cure out of round condition and other similar surface defects.

50 years on, we now know that warped disks requiring correction are extremely rare and that routine resurfacing at pad change is unnecessary.

Rotors themselves have changed in that they are no longer manufactured with any extra 'meat'. Machining away .003" may not sound like much, but if the rotor only has .015" margin in the first place, the 3 thou thrown away has shortened the rotor life substantially.

Jag may insist upon having machining capabilities available and recommend the sledgehammer approach to customer complaints, but it's interesting that this comment comes from the same source who dismisses Jag's recommendations for many other types of maintenance, irrespective of whether the concerns are substantiated or not.