I am no techical expert. So IMHO...

Initially I used to have my cars maintained by a Jaguar Main Dealer.
Very expensive. If in doubt, change it out ! Very profitable for the Dealer.

My old V12 used to 'pink/detonate' and after several costly attempts by the Main Dealer failing to fix the problem I called the Browns Lane Service Department. They suggested I try the Dealer one more time, or they (Browns Lane) would fix it.

I suppose I shouldn't have been surprised that the dealer fixed it, and refunded all my previous costs. I guess all it takes is a call from the right people !

So why is this relevant ? I quit using the Main Dealer and have been using Independents ever since.

When my guys say change the pads, I do. When they say change the rotors, I do. If I didn't trust them I wouldn't let them near my 155 mph machines. (There is another thread regarding maximum speed. I did 125 in my V12 and then backed-off).

I have never had noises from the new set-ups.

If you replace pads without the rotors the pads will take a little while to bed-in and 'adopt' the surface profile of the new rotors; and they will be less efficient until they do; but this doen't normally take many miles.

Don't we all take it a little easy after work has be done on our cars ? Just in case ?

Of course, if the rotors are badly 'grooved' it raises another question. Why ?

As I understand it, the potential problem with skimming is the heat dissipation capabilty of the rotor is reduced as the rotor becomes too thin.
It's never happened to me but rotors can explode (skimmed or not).
I have seen (Jaguar) vented rotors that have worn to the point where they are all vents, and no solid material either side of the vents ! The XKR did stop, but it needed the help of a very substantial tree. This was due to lack of maintenance, not poor quality rotors. Clearly, the 'skimming' was due to wear not design

Our XJRs are quick, very quick. I need to know mine will stop asap, if neccesary

So I stay with Jaguar approved parts. They may not be made by Jaguar, they may cost more then other brands (and less than some!) but they are made to Jaguar specifications.

We all pay our money and take our chance.

Best wishes to all, Rojie

 

There are certainly differing opinions on this (and other topics) topic on this forum and most of it is relatively correct if everything were equal and we all had exactly the same understanding of what 'a little' or 'a lot' actually meant.

To quote directly from the EBC website:

"It is a complete waste of money to fit new pads if your rotors are badly scored or hollowed. It is also dangerous and can cause a total loss of brake. Check rotor surface condition with a straight edge and if there is more than 0.5mm or 0.020 inches (twenty thousandths) of hollow the rotors must be turned or replaced. This can be done by any brake centre or most machine shops. If you DO NOT turn or replace the rotors you will have low efficiency/dangerous brakes for the first 1000 or more miles and you will tramline your pads and damage them. This is a safety issue and we strongly recommend having a professional mechanic advise if you are not capable of measuring this yourself. With brakes the motto is “Any doubts … see a mechanic”.

The above should give some guideline as to how much "wear hardened" surface is O.K. before it is machined away in the interests of maximum initial swept area.

In general it looks to me, from many comparisons, that a rotor should not be turned or "skimmed" more then about 2 mm from it's original thickness. Keep in mind that this is dependent upon the ability of the caliper to still push the pistons against the rotor surface with as much pressure as they could originally without running the risk of the piston to caliper seal being extended beyond it's limits thus allowing brake fluid to push out under pressure with disasterous results to braking ability. The thickness of any rotor isn't a universal constant but is engineered for the specific needs of the automobile and the type/size of the calipers to be used. Therefore the minimum thickness is also NOT a universal number and can differ by application. It just appears to me that the amount that may be safely machined from a rotor is in the neighborhood of 2mm, but even that is subject to the individual manufacturers recommendation which is usually stamped in the non-wear area at the center of the rotor.

Does any of that make sense or am I over thinking this? I do know from 50+ years of varied driving experience that the machining of rotors is an acceptable and safe practice within the recommended limits, and that a set of rotors is quite capable of going thousands of more miles then many on here think.

 

One more variable to the discussion.

Make sure the place you have machine your rotors DOES IT CORRECTLY!

In my shop, we check the run out (amount of parallel surface warp, usually .003-4 allowed) with a dial indicator on rotors along with thickness to determine replacement.
A rotor may have proper thickness left but may be too warped to effectively machine. You'll usually know if you have a warped rotor by the pulsing feel when you brake. I don't remember Seth mentioning a pulse to his braking but the following applies in any case.

Just because a shop CAN machine your rotors doesn't always mean they will do it CORRECTLY.

Besides smoothing the surface for better pad contact, machining trues up the parallel surfaces of the rotor but if the rotor is not correctly aligned on the lathe or the lathe has a bent hub, you may get back rotors that are worse than when you began. We had one shop do our rotors that would align them to remove the least amount of metal which near guaranteed a wobbly out of spec rotor every time. We don't have that shop turn our rotors anymore.

To be fair you even have to check new parts out of the box. I've measured stuff more than twice out of spec (.007-9) that was brand new. (even once opened a box to find a part I'd rejected weeks earlier with my findings still written on it!). This is why I tend to agree with the "if it is thick enough and not warped nor grooved severely, keep using the rotor you have as it is." school of thought. Pads are a consumable (well, rotors too, eventually) and even there you have so many variables even to compositions changing on known brands under the same name that it's possible to have over-hard pads wearing out your rotors prematurely. We had problems with Wagner Everstop pads doing this after they changed the material so that we have gone back to using factory pads in most cases as it is still cheaper to put on 3-4 sets of pads compared to 2 sets and rotors. Just a consideration.

If you have a good mechanic to work on your car, he'll make sure the ancillary shops he uses are good quality also, but when your doing the work yourself, be sure to check around as well as you can.

 

As my dealership doesn't like skimming, I usually replace the discs and would also balance the wheels afterwards. There is some vibration initially - with the steering wheel shaking to the left and right so vigously and embarrasingly that I have sought never to have passengers shortly after replacing the brake pads/ discs, lest they laugh at my lovely cat's appauling ride. The virbration disappears after a couple thousand kilometers of driving.

I feel that the car is heavier than the 1.8tons listed especially at low speeds. It feels heavy around corners at low speeds, and sometimes I feel it needs me to apply a lot of pressure to bring it to a halt. Whereas at higher speeds, it changes character completely and feels light around corners.

What I have also noticed is that if I suddenly accelarate (from low take off speeds) and immediately try to stop suddenly, the stoping distance is longer. It would feel like I need to apply excessive amounts of pressure to stop it. It's as if there is an opposite force pushing my foot away from the brake pedal! That's when I'd wish the brake pedal was double the size in broadness, so I can use both feet to stop the car.

I must say, having read all responses in this thread, I am more confused and concerned than I was initially. The other challenge for me is that, unlike in the UK and the US, in my city, there is a gap of ~40KM between the few dealerships in my city (there are 3 dealerships in a city of 10million people). Jags are not as popular as beemers, mercs and audi's are in my part of town. In as much as we Jag owners enjoy exclusivity, also we suffer from being suckered into doing what we are told by these limited dealerships.

The car is fantastic though, never boring and a good looker despite being over 9 years old!

I guess the safe route for me is to not replace ever 24 thousand K's, but ever 48 or so for now and see how it goes! I could then extend the mileage by another 24 and so on.

Thank you all for your kind words of wisdom and advice.

 

I guess I don't see the problem. You change pads when they are worn beyond limits--not mileage. The initial problems after replacement with old, unturned rotors should show you the folly of this course.

Your best course is replace the pads when they are worn out and use new quality rotors.

 

Seth,

I looked up the thickness and runout specs at work today and verified them with Mitchell online.

2003-2005 XJ8 and XJR brakes (May apply beyond these years but as far as I went)

Runout limits are the same for both standard and Brembo brakes.
Front Brake Rotor runout limit - 0.003 in or 0.076 mm
Rear Brake Rotor runout limit - 0.002 in or 0.070 mm
Runout needs to be checked with rotors installed, i.e. Wheels removed, calipers detached and wheel nuts tightened equally to 20 Nm.

Sometimes a faulty reading may result from dirt or corrosion between the hub face and the rotor mounting surface, so may need to remove and clean between surfaces then re check to be sure. Also a bent or faulty hub may cause vibrations as well.

Brake rotor nominal (original or new) thickness

Standard Front - 1.200 in or 30 mm Standard Rear - 0.800 in or 20 mm
Brembo Front - 1.280 in or 32 mm Brembo Rear - 0.600 or 15 mm

Brake Rotor discard at or less than thickness

Standard Front - 1.140 in or 28 mm Standard Rear - 0.720 or 18 mm
Brembo Front - 1.200 in or 30 mm Brembo Rear - 0.520 in or 13 mm

Thickness should be checked with a brake rotor micrometer (pointed to help read into grooves if necessary) at or near the outer edge of the rotor (usually about 3/8 of an inch).

I hope this helps you out a bit. So far the brakes on my XJ8L have been smooth and have plenty of pad left, so fortunately or unfortunately I haven't had to deal with them specifically yet. This is based on many brake jobs on other cars, vans and trucks. You are quite correct in having the pads checked out though, for I noticed in the Mitchell notes that the factory front pads have no "squealers" to let you know when the pads are low (usually 2-3 /32nds).

I realize this has gotten kind of involved, but this is what a good mechanic should be aware of when performing a brake job, especially on one of our beloved "Cats".

P.S. Have you had a four wheel alignment performed lately? That may explain the handling but road surfaces (especially grooved, worn roads) affect my car immensely even after the alignment.

Happy Motoring

 

The reason you are changing the discs is simply because you are a light braker, heavy braking causes the brakes to reach proper working temperature, this leads to friction material depositing on the disc, this is good transferance of material improves braking and reduces wear, the jag dealer should only change the disc if it wears below a certain thickness, regardless of the edge, i would expect to get at least 70-80k miles out of discs with 30 - 40 from pads, but you do need to brake harder or every now and then do a bed in procedure which gets the brakes up to fade temps and allows proper transferance of friction material, look it up in google there is plenty to read on the net, I learnt it years ago when working with rally cars and later when doing development work on specialist use vehicles.

 

Also, going back to the slottted rotors, I did and won't do again, far too noisy. And no real benefit as far as I can tell.

 

I believe this is the main cause of my issues coupled with lots of bumper-to-bumper surburban driving! I align and balance my wheels regularly and that is why I am able to put 80,000KM on the same set of tyres/ tires before they reach the minimum 3mm tread depth.

Thank you all for your insightful and valuable suggestions! I will now have to pay more fuel (gas) price in exchange for lower brake maintenance costs by increasing my driving speed a little and braking a little harder. I will now see which of the two evils is better to live with, and will keep you posted.

 

Just put a set of StopTech (Centric) slotted and drilled rotors and Centric semi pads. Couldn't be happier. Quiet and stopping better than ever. Go to the Centric web page and read how to break in your rotors and follow the information there.
www.stoptech.com/technical.../technical.../bed-in.../stock-brake-system-b...