I see at least two reasons never to visit that shop again.

 

Sorry to jump in on this but I have two cents worth of opinion as well. Some cars and motorcycles actually have discs that float. My BMW R1200C had floating discs. The disc part is held on with washers and rivet's which allows it to float and the caliper is mounted solid. I know some other cars are made this way but can't name them right off. Proper torque and so forth are helpful in keeping rotors from warping. But a lot of it depends on how the car is driven and if the rotor becomes hot then cooled with water as in a rain storm. You can machine or turn these down if they are in spec. But you won't really know until after you have turned the rotor to see if it's still in spec. Most places now have no freaking idea how to turn them. When I was a Corvette Tech for GM, I was sent to brake school and taught the proper way. If I decide to turn some, I just usually turn them myself at a parts store and just pay them for letting me use their equipment.

All rotors will be stamped min thickness on them for reference and you'll have to use a micrometer to check. You just can't visually do so.

 

07XKJaguar, most of are not certified like you are when it comes to brake work and we have used our "best judgement" (hence the many different views). From a manufacturer's point of view, did they ever mention something to the fact that rotors should be replaced even if they are just above the minimum thickness because after some wear with the pads, they will be below thickness or was the view that they have been engineered with a finite amount of wear calculated in and as long as you are above the mininmum thickness at the time of replacement, all should be fine by the end of normal pad wear?

I am just seeing if there might be some more technical justification of what is deemed "acceptable" and what is not. Most of us have not taken the time or gone to a school where you are taught how to do the indepth brake repairs. I think it might be helpful to get more of an engineering side of what is deemed ok.

 

Jaguars don't.

There's plenty of evidence to demonstrate that actual 'warpage' of rotors is pretty rare and that the most common cause of steering wheel vibration or pedal thumping is caused by pad material that has become deposited on the rotor face. This is easily removed with a sanding disc.

'Turning the rotors' is an outmoded practice that simply grinds away expensive material unnecessarily. It belongs in the same category as 3K mile oil changes.

 

I agree Mikey, not something I'm overy familair with here in the UK either tbh.

A disc / rotor is either good or bad, warped or not and either reused or generally just replaced with new.

 

I have been servicing Jags for over 15 years. To through my hat in the ring....short answer is no long answer is yes (I will explain) You do not have to replace rotors if they can me machined and stay above the min. thickness measurement. BUT try to think about how close you get to when you are done and how thick they will be while the pads are wearing.

As for the yes part. Most high end manufactures from Jaguar, Land Rover, Benz etc RECOMMEND rotor replacement with brake service because their customers expect brakes to perform a cretin way. Quite and smooth with no shaking. Best way to do that is to install new rotors with pads.

Other then customers overheating their brakes I have never had a come back when we change rotors. IF you really want to resurface them use a on the car lathe that will adjust for bearing run out. (that is why it is important to torque wheels)

 

Sometimes autocorrect can produce some hilarious errors.

Can you show us some factory recommendation from Jag about replacing rotors each time please?

 

Read this:

-Warped- Brake Disc and Other Myths

 

For every website that spreads the myth about pad material mysteriously sticking to the rotors and never coming off despite the brake pads wearing down themselves and the entire rotor, there's 2 websites that show that uneven torque on the wheel bolts of today's alloy rims cause the brakes to exhibit "warping" symptoms. Don't be blinded by the semantics of term warping. Just make sure you torque the wheels properly, and then you won't have to come up with crazy "aliens did it" ideas to explain why your brakes warped, because they won't.

 

Wheel nut torque cannot affect brake rotors. The wheel bolts to the hub and the rotor just sits on the hub.

There is no physical way wheel nut torque can affect the shape of the rotor.

Impossible.

Period.

 

But over torquing lugs on an aluminum wheel with an aluminum hub can cause vibration. I never torque over 90 ft-lbs for this reason.

 

Have you actually removed a rotor? Unless there's a securing machine screw (sometimes fitted to make installation of a wheel using bolts easier) I assure you the rotor just sits on the hub. Nothing holds it in place except the road wheel bolted on. It is physically impossible for the road wheel to be bolted on in such a way as to warp that rotor.

If you pop off the caliper the rotor just lifts off, unless there's a securing screw as mentioned. That securing screw is only there to ensure the unthreaded boltholes in the rotor hat line up with the threaded bolt holes in the actual hub which secure the wheel. If wheel studs are used the rotor just sits there.

 

I'm not advocating over torquing wheel nuts or bolts. There are good reasons to use only the specified torque. There is no way to warp the rotor unless the hub is also warped. Warping the wheel would be virtually impossible but even if it were possible the hub would also have to be warped which would wear out the wheel bearing very rapidly.

Brake rotors do not warp, as a rule, and they certainly don't warp from wheel bolt or nut torque.

Very hot rotors cooled very rapidly, such as driving through water with very hot brakes can warp a rotor sometimes. The more usual cause is uneven deposition of pad material causing run out at the disc surface. Because machining removes these deposits along with a bit of rotor you paid for even mechanics think the rotor was warped. After all their micrometer shows uneven thickness and their dial gauges also. They are misunderstanding what they are seeing as well as misunderstanding how it is getting fixed.

 

Only the uneven torque causation is a myth. The deposition of pad material (including pad imprinting) is well documented and well understood as a cause of "warping" symptoms.

One reason cast iron is used for discs is that it is porous and accepts a deposit from the brake pads which increases brake effectiveness. One reason ALL brake pad manufacturers specify a break in period for new pads, as do responsible car manufacturers.

 

Go ahead and torque one bolt on each of your front wheels to 1000 ft/lbs (easy to do by accident with a impact air tool), and the others to 100 ft/lbs. Then drive around for a few months, and let us know how your brake job to repair the warped discs goes for you?

 

1000? Really?

 

Yep. If you have an industrial unit like these pro shops do, and not the home depot special you have in your garage.

 

The studs would shear long before any such torque value was achieved.

 

Yea, no. Go ahead and try it if you don't believe it.

 

We need not since you have already done this.

Please post photos.

I'd like to see the equipment used so please post the links to where this equipment can be purchased, if at all possible. Remember the impact wrenches in use for these applications will be 1/2 drive.