Jagular - albeit on a different vehicle but the premise is exactly the same. I have to strongly disagree with your statement. I myself as stated have fitted 2 sets of NEW pads to USED discs on my Audi A6 before replacing with new pads AND discs all round, this was at around 86k miles iirc

The discs were only just approaching minimum thickness at that point!
This was as checked by a qualified Audi Tech.

Please remember that all OEM's generally factor in many safety points whilst making recommendations, so their minimum thickness actually means there's probably another 6 months or so of usable life....they always err on the side of caution.

Similarly the X type for example came with 130bhp or 153 bhp, however both could be remapped to 155bhp or around 180bhp quite safely. Some however went further and took their remaps above and beyond those "safe" figures.

IMO for what it's worth, replacing new discs with new pads every time is simply madness and a waste of resources, time and money.
You should bear in mind that everything generally has a weak point engineered into it, usually the easiest, quickest and cheapest part to replace, in this instance the pads.

 

Rather than all of the aforementioned and last postings, I'm more interested in whether the OP has actually made any progress on this issue?
Hope to hear....

 

FAQ's - EBC Brakes

http://ebcbrakes.com/articles/how-an...-brake-rotors/


Brake Pad Bed-In

Just two authoritative sources.

Modern street brakes are designed to wear the pads and rotors at equivalent rates.

You may well use your brakes so gently all of the time that you can get away with using a second set of pads on a set of rotors but you would be the exception.

The way I use my brakes I replace discs and pads as a unit every time. I used to replace discs only every second pad set but times have changed and that no longer works.

If you change pad material you MUST use new discs or re face the old discs.

Brakes are heat dissipation devices. Thin rotors run hotter, work less well and wear even faster than new discs.

 

The two articles you quoted do not support any of your claims, either immediately above or those stated previously. As has been practised by the vast majority of mechanics I've run into and as backed up by the article you quoted, rotors are to be evaluated during brake service to determine suitable action. There is NO mention of automatic replacement or resurfacing.

Hopefully the lady who initiated this thread is still following along and has not been scared off by sky-is-falling exaggerations. This is what brought her here in the first place.

 

Sorry Jagular, can't agree with you on that, it's just not cast in stone, or as cut n dried as that.

I and many others here both in the UK and overseas I'm sure, have been driving this way for many years, replacing pads / discs in this manner with no issues, none whatsoever.
Of course check the discs, but If not needed changing them is both costly and unnecessary.
If done correctly, the sky will not fall ( to paraphrase ) or the world end if discs are not changed at pad change times, assuming there is sufficient life left

 

Brakes bed in by rubbing pad material into the faces of the discs. Until that is completed you do not have full braking power. You won't notice this unless you ask for full braking power. After you rear end somebody you won't know why that was.

If you change pad material the wrong pad material is embedded in the rotor faces. That may or may not make a difference to braking power but odds are it will.

I understand people have been fitting new pads to old discs for a long time. I used to. You should not. In fact, you MUST not if you want full braking power as soon as possible and for the full life of the pads.

You do not save any money using old discs, or at least not enough money to compensate for the serious adverse effect on available braking power.

Much the same discussion arises when one points out that tires MUST be replaced when they are 5-7 years old whether they have tread left or not and when tread depth is reduced to 4/32 (3mm) rather then the legal minimum of 2/32 or 1.5 mm. Old ideas are now revealed to be dangerous old ideas.

 

They do if you read them carefully. I understand the argument that with proper machining old discs may be safe to re-use but they won't last for the full depth of the new pads. Thinner discs just do not brake as well as the thicker new discs. Also, the only actually warped rotor I experienced had been machined and warped about halfway through the pad life. The disc got hotter than it should have being too thin and then got cooled too quickly in the rain, warped instantly. I no longer permit my mechanic to machine old rotors. I fit new ones with new pads every time.

 

With that logic, I have been involved in an accident in the rain. So should I never drive in the rain again? I was in a vehicle when that happened...should avoid those as well. And I was outside my home as well, better to stay inside then.

There is an old saying, once is an occurrence, twice is a coincidence and three times is a pattern. Sounds like your data is thin with a sample size of one. As a collective, we have far more data to the contrary and have reused rotors many, many times on many vehicles.

Not sure that I would track a car with reused rotors that were getting close to min thickness, but so what if you had to replace them if one happened to warp. The car would still stop, just not as predictably. I have enough skill to drive through that condition, so it doesn't concern me, nor should it concern anyone driving sanely on a public road.

The true answer here is what is a new rotor's thickness? What is the min? And where am I now? If more than 50% left, keep them. If less replace. It's a simple mathematic equation.

And I like being away from my house driving in the rain...it's a risk I'm willing to assume (sound of microphone dropping)

 

Sure, I understand the safe driver argument as well.

Put it this way, my wife is an excellent driver but knows very little about her car.

I ensure the brakes, tires and steering system on her car are always in as close to perfect condition as can be arranged.

I persist in posting against the current of opinion because I firmly believe that the advice I have received to always replace discs when fitting new brake pads is superior advice.

There are those who still think they know better but the facts are clear: fitting new discs when fitting new pads is now best practice.

Just btw your logic is flawed. If you have an accident in the rain and you find that your tires were worn below 4/32 you should never drive in the rain again with worn out tires. Better yet, when your tires are worn down to 4/32 (or are 5-7 years old depending on the type of tire) replace them before it begins raining.

 

Jagular - your comment about receiving "superior advice" only seems to be taken on board by you, not the other 99%
Having said that, if that's how YOU feel and YOU are happy with it, then it's your car and your choice, but I and many others simply don't agree, period.

As for "best practice"
Best practice for who?
Is this simply YOUR mechanic, because no other Jaguar dealer or Indy I know specifies that new discs MUST be replaced with new pads, EVERY CHANGE.

As usual, we'll agree to disagree...

 

Still looking for any 'facts' to support your arguments ...............

 

I thought we were talking about brakes, not tires? And the accident I was in wasn't even caused by me or the condition of the car. I was simply making the point that you can't always attribute cause and effect based on one occurence. Otherwise you become a slave to such things, which then become superstition/paranoia, and a real limiting factor in life.

 

OK guys…..we get it…..now for God's sake, give it a rest !!!

 

Well, the facts are the mechanics I rely on say so.

The logic is as follows :

Let us say the XF brake discs when new are 20 mm ( not far off actually). Let's say the minimum allowed thickness is 17 mm. After one set of brake pads the disc are 18.4 mm thick. New disc or not? Clearly, after the second set of pads wears out the discs will be below minimum thickness. Therefore you should have changed the discs with the pads.

OK, so you say, as some do, that the minimum thickness doesn't mean minimum thickness it means minimum thickness when you fit a new set of pads so it doesn't matter that the discs are below minimum thickness after the second set of pads wears them out. That is incorrect but let us say it is ok. So, where do you draw that line? If by chance the discs are at 17.2 mm after the second set of pads is it ok to fit another set of new pads to old discs?

Logic drives you to understand that if the discs are half worn when the pads wear out then you fit new pads and discs. Discs actually wear faster as they get thinner because they get hotter more often.

I accept that maybe you will experience less than half thickness wear on the first set of pads. You might even get a full second set of pads out of the same discs but the chances are very good you will not.

So, if you care about safety you fit new discs every time you fit new pads. Especially if you know very little about cars. That's what the best mechanics are advising. It is wrong to advise otherwise.

 

brakes need to be evaluated on a case by case basis, if there's more than 50% rotor life remaining after 1 pad change there shouldn't be a need to change the rotor.


rotor thickness should be checked EVERY SERVICE and replaced when they are close to or fall below minimum thickness regardless of pad wear.

 

I wonder if the lady ever got her brakes fixed? Maybe wrong question, I wonder of the lady ever got her brakes fixed with necessary parts at reasonable commercial prices?

 

Yes I think we're all wondering if the lady in question ever got this resolved?
Meanwhile the debate rages ever onwards......


It's always good to get a thread to a conclusion, hopefully she returns and advises where she's at and if it's resolved shortly

 

The question is do you replace them if there's less than 50% disc thickness remaining?

 

No wonder you're throwing so many serviceable rotors away. The minimum thickness is a decision threshold for putting the rotor back into service. If at or above, it's good to go. If not, scrap.

A mechanic would have no idea how many sets of pads have been on a rotor nor would he necessarily know the thickness of a new rotor. There is no way for him to calculate the future wear rate of a rotor without both pieces of info.

Go ask any OEM if you don't believe me.

 

The crazy thing is, that Jaguar, like most other OEM's will factor in a safety margin, on the safety margin, to allow for mechanically minded or tech challenged owners.

If the disc thickness starts at 30mm for example on vented fronts, the minimum thickness may be 28mm ( these are just rough examples )
In all likelihood the real minimum recommended thickness may be around 26mm, but Jaguar or any other OEM will never tell you that, choosing to always err on the side of caution.

I am NOT saying or advising it's ok to run below the minimum thickness, just that you don't have to worry about changing them with 20% or 30% of usable life left in them