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Rotors or brake discs MOST certainly do warp. They are made of medium grade cast iron and will heat and cool differently in different places. Having been in the trade for nearly 40 years I have seen and measured countless brake discs that are completely clean yet warped to over 0.2mm. It is very important when replacing discs and pads that the hub is machine cleaned. I have an ATe hub buffer that is driven by the impact. As I am BMW trained and all BMWs have bolts the hub is only drilled. For Jags where the hub is fitted with studs, you can buy an ATe buffer that fits over the studs and in between. The hub must be clean and rust free before you put the disc on. You must also ensure the pad and calliper carrier is clean where the pads slide. There are special files that fit in the groves but a good wire brush and a screw driver work. If the calliper carrier uses stainless pads shims it is even more important to clean the groove else there will be excessive tension on the pad thus making them likely to stick. If the pads stick they will heat the disc up slowly and continuously. If the disc is pretty warm without your foot on the pedal, the massive heat induced by braking risks sending temps up into a zone above normal "excess" heat norm. This happens a few times and hey presto warped discs. Proper brake maintenance involves measuring tools to check runout. I do it every single time!
I would legitimately love to know why it matters whether the rotor is warping or if there uneven deposition of brake material. The end result is the rotor is no longer smooth and runout exists,no? What is the significance of the cause? Is this just an exercise in semantics?
The significance of the cause always matters. It's all about the consequences. Just ask any physician who is diagnosing a patient's illness with symptoms that point to many possible illnesses, each with different treatments. Knowing the exact cause determines the proper treatment. It could be the difference between life and death.
Symantics matter. As does pronunciation. My favorite example is the difference between a burrow and a burro.
A burrow is a hole in the ground made by many kinds of small animals, such as moles, voles, chipmunks and rats. A burro is a small donkey, usually used as a pack animal.
Here's why it matters: homophones are words that sound the same, but have different meanings. An example is flower and flour. Burrow and burro technically aren't homophones, but some people mispronounce them so they sound the same.
Bottom line: If you don't know the difference between a burro and a burrow, you don't know the difference between your a** and a hole in the ground!
Over the years I have tried the Italian brake job and the Italian tune-up. It has never done anything for me (other than make me look like a lunatic). For pulsating brakes, I have always needed to skim or replace the rotors. Thus, for me, the solution has been the same regardless of the cause.
However I agree that the cause could matter if, for example, the composition of pad alters the deposition of material on the rotor. I’m unaware of such information, however if it does exist/ is common knowledge then doubtfully would anyone perpetuate the idea that rotors are to fault.
I’ve been working on cars for the past 40 years and while I think maybe some rotors can warp I don’t think it’s all that common and I am of the belief that most pulsating brake pedals are due to the build up of material
and every car I’ve had with pulsating brakes ive run the bed in process where are you do three panic brakes(hard without locking em) from 50 to 30 and then another three stops from 40 to 20 in quick succession. Do not come to a complete stop and then drive continuously for 5 to 10 minutes without touching the brakes to let the brakes cool down completely.
my Theory why some people keep having the same pulsating brake problem is because of the way they drive in the way they break. The material gets deposited when you come to a stop and you sit on the brake pedal and grind the pad into the desk that’s when the transfer occurs. So if you do a lot of stop and go or if you ride your break without realizing it and then come to a stop you’ve heard that pad in that disc up more than most people so if you come to the stop you deposit more material and that’s why certain people have a reoccurring problem
Doing the brake bed in process doesn’t cost you anything if you do it correctly it might save you a lot of time and money replacing parts but is very important to follow the instructions verbatim. Because if you decide to use those brakes after this super hot you’ve just redeposit material back on the rotors so you need to make sure you cruise for a good 5 to 10 minutes without touching the brakes at all after bedding them
I’ve been working on cars for the past 40 years and while I think maybe some rotors can warp I don’t think it’s all that common and I am of the belief that most pulsating brake pedals are due to the build up of material
and every car I’ve had with pulsating brakes ive run the bed in process where are you do three panic brakes(hard without locking em) from 50 to 30 and then another three stops from 40 to 20 in quick succession. Do not come to a complete stop and then drive continuously for 5 to 10 minutes without touching the brakes to let the brakes cool down completely.
my Theory why some people keep having the same pulsating brake problem is because of the way they drive in the way they break. The material gets deposited when you come to a stop and you sit on the brake pedal and grind the pad into the desk that’s when the transfer occurs. So if you do a lot of stop and go or if you ride your break without realizing it and then come to a stop you’ve heard that pad in that disc up more than most people so if you come to the stop you deposit more material and that’s why certain people have a reoccurring problem
Doing the brake bed in process doesn’t cost you anything if you do it correctly it might save you a lot of time and money replacing parts but is very important to follow the instructions verbatim. Because if you decide to use those brakes after this super hot you’ve just redeposit material back on the rotors so you need to make sure you cruise for a good 5 to 10 minutes without touching the brakes at all after bedding them
+1.
I have replaced/renewed pads and/or rotors (discs) on all three of my Jags (2010 XFS, 2010 XFR and 2014 F-Type) several times, and I ALWAYS bed the new pads/discs in using the repeated heavy braking procedure you have detailed. And making sure I go for a "cool down lap" afterwards!
Surprise surprise I have NEVER had any brake judder or vibration or any other brake problem.
Not sure what I will do the next time I renew the pads and/or discs as the heavy repeated braking now makes me nauseous, I suspect I will get someone else to do this.
Over on the Pommy XF forum there are literally hundreds of posts about "brake judder" with many owners paying for new discs over and over. It's only in the last couple of years they have come to the realisation that it's not caused by "warped discs", rather it is caused by either or both of uneven pad material deposition and sticking caliper slide pins. So that's another thing to consider on your X351s, sticking caliper slide pins which seems to be quite common over in cold wet and salted roads Blighty! Also lots of debate if the slide pins should just be cleaned or also lightly greased, I have always lightly greased my pins with high-temp ceramic brake grease and never had a problem.
I have heard that before, and thus I always perform the bed in process. Perhaps I would have had more frequent issues with pulsating brakes had I not done that; who knows.
Interestingly after my last rotor issue, I called the vendor, R1 Concepts and asked them to confirm their recommend break-in process. They replied that it is no longer necessary.
Edit: In regards to the slide pins, admittedly I noticed mine were rather dry upon swapping out the rotors. That was corrected during the swap and all slide pins were regreased at that time. So indeed that may have played a role with my last rotor.
I have heard that before, and thus I always perform the bed in process. Perhaps I would have had more frequent issues with pulsating brakes had I not done that; who knows.
Interestingly after my last rotor issue, I called the vendor, R1 Concepts and asked them to confirm their recommend break-in process. They replied that it is no longer necessary.
Edit: In regards to the slide pins, admittedly I noticed mine were rather dry upon swapping out the rotors. That was corrected during the swap and all slide pins were regreased at that time. So indeed that may have played a role with my last rotor.
The Pommy forum debate over "should the slide pins be greased or not" centres around dirt and dust settling on/around the slide pins, particularly brake dust.
As we all know the OEM Jag brake pads are incredibly dusty.
Some argue that any grease on the pins attracts and holds this dust, it builds up, and eventually causes the slide pins to stick.
Others claim (with evidence) that the bores in which the slide pin rubber/plastic sleeves fit rust and bubble, squeezing the sleeves inwards which then in turn squeeze the pins.
I have never seen this rusting, I suppose because I live in a dry climate with zero snow and zero road salt.
I also argue that the rubber plugs on the outsides/ends of the plastic sleeves prevent any dirt or dust from getting in and sticking to the slide pins. My evidence is that I have removed, cleaned and greased these pins many times and every single time they were completely clean and dust free other than for the previous grease I had applied.
The Pommy forum debate over "should the slide pins be greased or not" centres around dirt and dust settling on/around the slide pins, particularly brake dust.
As we all know the OEM Jag brake pads are incredibly dusty.
Some argue that any grease on the pins attracts and holds this dust, it builds up, and eventually causes the slide pins to stick.
Others claim (with evidence) that the bores in which the slide pin rubber/plastic sleeves fit rust and bubble, squeezing the sleeves inwards which then in turn squeeze the pins.
I have never seen this rusting, I suppose because I live in a dry climate with zero snow and zero road salt.
I also argue that the rubber plugs on the outsides/ends of the plastic sleeves prevent any dirt or dust from getting in and sticking to the slide pins. My evidence is that I have removed, cleaned and greased these pins many times and every single time they were completely clean and dust free other than for the previous grease I had applied.
same.
grease the pins. Replace the pins if they’re worn or pitted.
rubber seals on the pins are designed to keep the dust and the water out and any grease that is up underneath that rubber seal will catch any potential brake dust w trying to get into the pin area and will effectively block it. I remember in the old days we used to take grease and smear it on the inside of the wheel bearing cap that goes over the front wheel bearings of my old Dodge and that was supposed to catch any dirt that gets into that bearing area.
I’ve been working on cars for the past 40 years and while I think maybe some rotors can warp I don’t think it’s all that common and I am of the belief that most pulsating brake pedals are due to the build up of material
and every car I’ve had with pulsating brakes ive run the bed in process where are you do three panic brakes(hard without locking em) from 50 to 30 and then another three stops from 40 to 20 in quick succession. Do not come to a complete stop and then drive continuously for 5 to 10 minutes without touching the brakes to let the brakes cool down completely.
my Theory why some people keep having the same pulsating brake problem is because of the way they drive in the way they break. The material gets deposited when you come to a stop and you sit on the brake pedal and grind the pad into the desk that’s when the transfer occurs. So if you do a lot of stop and go or if you ride your break without realizing it and then come to a stop you’ve heard that pad in that disc up more than most people so if you come to the stop you deposit more material and that’s why certain people have a reoccurring problem
Doing the brake bed in process doesn’t cost you anything if you do it correctly it might save you a lot of time and money replacing parts but is very important to follow the instructions verbatim. Because if you decide to use those brakes after this super hot you’ve just redeposit material back on the rotors so you need to make sure you cruise for a good 5 to 10 minutes without touching the brakes at all after bedding them
