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It’s cast iron not steel. It cuts almost like an aluminium. You could easily make it worst by a belt sander unless you could somehow have the disc spinning when doing this to make it uniform.
I definitely wouldn't use 100 grit with a machine. Maybe by hand to finish it though.
 

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So, how do you get the brakes hot enough to bed them in, but cool enough not to glaze them?

Asking for a friend.
 

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So, how do you get the brakes hot enough to bed them in, but cool enough not to glaze them?

Asking for a friend.
Good question!

As for mine, they are biting much better now and seem to keep improving. There is slight judder still there but far better than before.

The braking itself is different, even with the lesser bite, but different in a good way. I had to hit the brakes hard on Sunday and it feels like the car has more braking power, but without the ABS having to kick in. It's hard to explain but it's almost like I've got bigger brakes or a larger contact area. It's not overwhelmingly noticeable but not subtle either, either way I'm pretty happy with the results so far and my wear sensor has stopped showing a warning as well so result there! lol
 

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.... it feels like the car has more braking power....
A result of proper breaking in pads and rotors if I understand the process correctly. You end up with a thin (microns) film of pad material deposited evenly throughout the contact patch on the rotors giving the ideal coefficient of friction.
 
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Discussion Starter · #187 ·
So, how do you get the brakes hot enough to bed them in, but cool enough not to glaze them?

Asking for a friend.
I had attached an comprehensive pdf that I found recently. It seems impossible that you could reach glazing temp if followed the procedure correctly. It says there should be a grey tint left on disc once done properly. Also the accelerations in between brake cycles should let it cool down a bit. I think glazing happens mostly when the pad is touching the discs for an extensive amount of time.
another interesting point in the pdf is that judder could happen regardless of pad type that is confirmed here by some people using red stuff. The key seems to be using dial indicator and have the disc as flat as possible “after” putting the wheel on and then head to a motorway to bed it in.
 

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Yeah, I followed the EBC bedding in procedure, which (depending on where you look on their website) is 10 rapid stops from 60-10, or 5 rapid stops from 60-10, followed by another 5 after the brakes have cooled.

I did the 10 stops in succession, as I only found the 2 x 5 stops a week later.
 

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....I had attached an comprehensive pdf .....
I disagree with their premise that varying disk thickness causes steering wheel judder. That causes pulsating at the brake pedal. It probably would lead to hot spots with deposits that would cause judder though. It would also mean that the casting material had imperfections/poor quality control and would probably affect a batch of rotors because the finish machining trues the rotors.

.....the disc as flat as possible “after” putting the wheel on...
Corrosion or foreign material under top hat mating surfaces can cause this problem.
 

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Discussion Starter · #190 ·
I disagree with their premise that varying disk thickness causes steering wheel judder. That causes pulsating at the brake pedal. It probably would lead to hot spots with deposits that would cause judder though. It would also mean that the casting material had imperfections/poor quality control and would probably affect a batch of rotors because the finish machining trues the rotors.



Corrosion or foreign material under top hat mating surfaces can cause this problem.
They actually say the mechanisms are different but the effect are the same.
 

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When I put my new TRW disks/ceramic pads on the juddering completely disappeared, as mentioned earlier.
On my forst run I performed 5 relatively hard braking from 100 km/h to 10 km/h but not hard enough to smell burnt disks/pads. The Powerstop pads are apparently "pre-scortched", which I presume means they have been heated somehow. Would this help the bedding-in procedure?

I understand and agree with the principle of cementite build up on discks, however this should only happen when very hot pads/disks are in significant contact over a prolonged period (e.g. pressed against eachother more than about a second or so). My problem with respect to the sensitivity of XFs is that there seems to be many here who take care to not keep the brakes on when stopped. I myself have been more careful since last changing the discs a year ago and I also try not to use the EPB either, but instead come to a stop in "N" and release brakes just before stopping. If on a slope, then try to engage "P" rather than apply the EPB. This is especially true after heavy braking. Regardless of these precautions, I still developed judder! None of my other cars (with same driving environment/conditions) have ever or do suffer from this phenomenon. That includes our Ford Galaxy which is often fully laden and heavy.

My personal theory is that the XF calipers are simply not allowing the pads to release from the disks sufficiently when the brake pedal is released. This may then account for some heat-dependent pad transfer to disks when stopped after braking, even when the brake pedal/EPB are not on. Indeed Jaguar themselves recommend upgrading to stronger EPB return springs, and I did this recently. For me both rear and front disks appear to cause problems with juddering.

Would be great to have some sort of real-time pressure sensor for pad/disk contact.
 

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Discussion Starter · #192 ·
Scorched pads are more stable under temperature but this phenomenon is all about discs. They should have find a way of bed discs before leaving the factory unless they cannot due to protective layer. Lower quality discs should be more prone to this but I doubt it’s easy to check discs for homogenous properties in all surface areas before they leave factory.
I think it’s the weight of the car that contributes in this. For lighter car you probably cannot take discs a s pads hot enough for this to start. That pdf talks about microscopic hot spot even though the disc is only warm. The reason I buy the idea is that my front discs look brand new, worn very evenly and no circular grooves. Dial indicator shows 0.05mm runout that should be acceptable by many standards. Then I have the judder and it varies from time to time. If I engage brake quickly and then continue as normal there is less judder than I slowly engage it. After using shims, I only have judder over 50mph. If it was DTV I should have some at any speed. I have noticed a couple of times, if I depress pedal very very slowly to stop at traffic light, car steers to left or right like when tyre on one side is low on pressure. Probably oil on hands or gloves during installation of the disc would contribute to this if bed in is done immediately after installation. Many people just spray brake cleaner and not wipe it off.
 

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....Scorched pads are more stable under temperature but this phenomenon is all about discs.....
+1M Break in is more than not applying pressure to the pads when heated up. It's also about material transfer from the pad to the rotor. After break in and cool down sequence it should be safe to hold at stops. Yes, I'm on a mission for people to understand brake judder:)
 

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+1M Break in is more than not applying pressure to the pads when heated up. It's also about material transfer from the pad to the rotor. After break in and cool down sequence it should be safe to hold at stops. Yes, I'm on a mission for people to understand brake judder:)
……..and your mission is most appreciated….!
 

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Discussion Starter · #195 · (Edited)
You have probably seen this video:

I took a couple of screenshots that show interesting results that could help you control temperature during the break in. In 60 to 3mp test, all pads including ceramics and cheap semi-metallic pads get to around 450C after 5 brakes and around 550C after 10 brakes. None of other tests could increase temp above 200C. Also the temperature does not increase that much after first 5.

186720

Red curve is temperature, blue is friction coefficient and green is brake line pressure (showing needed pedal force). Acceleration is -0.4g meaning it takes 6.7sec to get from 60mph to 3mph and car will travel around 100m.
Based on this, my impression is that for those on economy pads, I will keep number of brake applications around 5 to 7. For high performance pads, probably minimum 10 brake applications needed.
If you brake harder (meaning drop the speed considerably below 6.7sec) you need less brake applications and if you do it slower, you need more. I think 6.7sec is good enough to avoid thermal shock to the bonding material of the pad by letting temp to raise in a slower rate.
 

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Really interestful, Hamed, but I genuinely think we are turning this into a scientific heap of pish. At the risk of repeating myself myself, JLR know fine fekn well there is a problem here, but to admit any kind of “concern“would be to instigate a really major recall, as recalls are genuinely mainly to do with SAFETY issues, which brakes come under.……hopefully. They have your money, so thereafter, GFYS.
 

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My judder is back. :(

Figured sod it, let's do another session. Brake judder gone, but glazing is back - which I think was masking the judder before and now again.
 

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Discussion Starter · #199 ·
I doubt even JLR knows why this happens. Otherwise they would fix brand new cars instead of replacing brake discs and pads under warranty.
All they can do is to switch to another type/brand of brake system that are known to be better.
I would be really annoyed if the judder is back quickly. That’s why I am thinking a lot before changing all discs and pads. It seems Fords have had this issue for decades and it’s probably inherited from ford but my S-type never had this issue!
Judder is one think, sometimes I can feel all suspension is going to worn out quickly because of it.
 

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Discussion Starter · #200 ·
My judder is back. :(

Figured sod it, let's do another session. Brake judder gone, but glazing is back - which I think was masking the judder before and now again.
Would you remind me how old are discs and pads?
 
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