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      09-27-2016, 04:08 PM   #45
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Yes but they are actually LESS expensive all said and done if you just use them for street use...

I have them on my M6 (not a track car) just for their improved performance and absolutely no brake dust. They will last forever on a street car and your wheels will stay absolutely clean without any work on your part. The carbon dust just blows off during normal driving and/or can be rinsed off with just a hose...
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      09-27-2016, 09:20 PM   #46
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Interesting perspective. Its a 8900 dollar option in Canada. I honestly doubt I would spend that much money on replacing pads/rotors in the time that I intend to keep the car (max 5-6 years). I do like the fact about the wheels staying clean but that's a steep price to pay for that purpose. I doubt for street use that I would need them or that they are miles away from the standard steels. Just my thoughts.

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      09-27-2016, 09:48 PM   #47
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Wow. $17K in consumables for an $8K factory option which ironically enough is meant to be used a certain way.
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      09-28-2016, 10:50 AM   #48
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For those that are following the details, I just got a set of representative weights for the REAR CCB rotors from my friends at the PDC. They pulled a couple of brand new M3/M4 REAR CCB rotors to measure the weight when NEW and then also recorded the min weight as stamped on each. This tells us how much usable "meat" is on the REAR Rotors (by weight):

New REAR Rotor Info (Weight New - Min Weight = Usable Weight):

Sample 1: 5796g - 5764g = 32g
Sample 2: 5778g - 5734g = 44g

and just to repost:

New FRONT Rotor Info (Weight New - Min Weight = Usable Weight):

Sample 1: 7356g - 7165g = 191g
Sample 2: 7294g - 7096g = 198g

So it looks like the fronts have about 200g of usable meat on them and the rears have about 40g (maybe even 40-50g).

Note that these two sets of NEW rotors were weighed by different shops so the values might be slightly skewed for differences in equipment. My BMW SC weighed the new front rotors and friends at the PDC weighed the new rear rotors.

This might be useful in helping to determine how much useful life is left on your CCB rotors if you weigh them.

The front rotor my shop weighed had 141g left (7356-7215) which would indicate about 70% life remaining!

The rear rotor my shop weighed had 68g left (5802-5734) which seems to be well above what we would expect on a new rotor (40-50g) - so that measurement is suspect.

I have both of the fronts which were removed and carefully re-boxed. I also have a scale on order. I'm going to thoroughly wash/clean/dry the two front rotors I have and re-weigh them to see how my numbers compare to those obtained by my shop.

BMW has left us kind of out in the cold with respect to CCB maintenance. They give us the wear indicators, min weights, and how to identify failed/chipped rotors but not much other info is to be found. I wish they would step up and give us the following two pieces of info in formal correspondence:

1. What happens when your CCB Rotor drops below the stamped "min weight"? Do we just lose braking effectiveness/performance or are we in jeopardy of a catastrophic rotor failure? Losing performance is not a big deal but having a rotor crack/split/delaminate/explode certainly would be! If its the former, then we can just keep weighing them and replace them AFTER we cross the threshold (or experience a loss of performance). If its the latter, then it would be recommended to replace them BEFORE we cross the threshold.

2. Officially, what is the usable/consumable weight on each type (front/rear) of rotor? If we need to replace the rotors BEFORE we cross the min weight threshold, then it would be a good idea to know how fast we are approaching that value. In order to estimate that value, we need to know what we started with and what we have left. Without this info, we don't really have any way to estimate how many track days we have left on the rotors.

My shop and our friends at the PDC have given us what info they can. I'm going to reach out to a couple of contacts at BMW DE to see if they can get me in touch with the right person/people to help get more precise answers the above questions...

I'm also considering getting one of the Carboteq instruments. I know that sounds crazy but it may be the only reliable method available. If it saves just one unnecessary rotor replacement, it would pay for itself. Maybe I can rent it out (to my shop)...
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      09-28-2016, 12:25 PM   #49
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Quote:
Originally Posted by evanevery
For those that are following the details, I just got a set of representative weights for the REAR CCB rotors from my friends at the PDC. They pulled a couple of brand new M3/M4 REAR CCB rotors to measure the weight when NEW and then also recorded the min weight as stamped on each. This tells us how much usable "meat" is on the REAR Rotors (by weight):

New REAR Rotor Info (Weight New - Min Weight = Usable Weight):

Sample 1: 5796g - 5764g = 32g
Sample 2: 5778g - 5734g = 44g

and just to repost:

New FRONT Rotor Info (Weight New - Min Weight = Usable Weight):

Sample 1: 7356g - 7165g = 191g
Sample 2: 7294g - 7096g = 198g

So it looks like the fronts have about 200g of usable meat on them and the rears have about 40g (maybe even 40-50g).

Note that these two sets of NEW rotors were weighed by different shops so the values might be slightly skewed for differences in equipment. My BMW SC weighed the new front rotors and friends at the PDC weighed the new rear rotors.

This might be useful in helping to determine how much useful life is left on your CCB rotors if you weigh them.

The front rotor my shop weighed had 141g left (7356-7215) which would indicate about 70% life remaining!

The rear rotor my shop weighed had 68g left (5802-5734) which seems to be well above what we would expect on a new rotor (40-50g) - so that measurement is suspect.

I have both of the fronts which were removed and carefully re-boxed. I also have a scale on order. I'm going to thoroughly wash/clean/dry the two front rotors I have and re-weigh them to see how my numbers compare to those obtained by my shop.

BMW has left us kind of out in the cold with respect to CCB maintenance. They give us the wear indicators, min weights, and how to identify failed/chipped rotors but not much other info is to be found. I wish they would step up and give us the following two pieces of info in formal correspondence:

1. What happens when your CCB Rotor drops below the stamped "min weight"? Do we just lose braking effectiveness/performance or are we in jeopardy of a catastrophic rotor failure? Losing performance is not a big deal but having a rotor crack/split/delaminate/explode certainly would be! If its the former, then we can just keep weighing them and replace them AFTER we cross the threshold (or experience a loss of performance). If its the latter, then it would be recommended to replace them BEFORE we cross the threshold.

2. Officially, what is the usable/consumable weight on each type (front/rear) of rotor? If we need to replace the rotors BEFORE we cross the min weight threshold, then it would be a good idea to know how fast we are approaching that value. In order to estimate that value, we need to know what we started with and what we have left. Without this info, we don't really have any way to estimate how many track days we have left on the rotors.

My shop and our friends at the PDC have given us what info they can. I'm going to reach out to a couple of contacts at BMW DE to see if they can get me in touch with the right person/people to help get more precise answers the above questions...

I'm also considering getting one of the Carboteq instruments. I know that sounds crazy but it may be the only reliable method available. If it saves just one unnecessary rotor replacement, it would pay for itself. Maybe I can rent it out (to my shop)...
This thread deserves sticky status.

The measured weights lean heavily towards the PDC scale being under by approx 0.5oz and the dealer scale around 1.5oz over. The calibrated new weight of the original and replacement discs at the time of manufacturing. It should be attached to the vehicle history in ISIS. If not, they can be obtained from BMW using the serial number on the hat.

To put the difference in scale tolerance and in-service weight loss into perspective for everyone, grab 10 quarters. Barely notice the weight right? That's within a fraction of 2oz/60g or the change between a new and close to/at end of life disc.

The Proseq is insanely accurate and easy to use. It is VERY expensive and VAG has rights to it for a bit in the US. Make nice with a local Porsche tech and borrow it from time to time.
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      09-28-2016, 01:04 PM   #50
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Quote:
Originally Posted by lemetier View Post
This thread deserves sticky status.

The measured weights lean heavily towards the PDC scale being under by approx 0.5oz and the dealer scale around 1.5oz over.
I have the original boxes that the replacement (NEW) front rotors came in. (My USED rotors are now packed in them). Do you think the original weights are somewhere on the box? I have not looked for it...

Also, how are you obtaining your estimates of scale discrepancies (PDC under by 0.5 oz and SC over by 1.5 oz)? I also think there are some inaccuracies involved, but how did you come by those specific numbers? ...and why are your estimates in ounces and not grams? I actually have photos of the PDC scales as they measured the weights. They used refrigerant scales and the scales indicated grams directly. Not sure what the SC used...

0.5 oz = 14.2 g
1.5 oz = 42.5 g

BTW - The Carboteq is "only" $6500.00 compared with the one you have identified...
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      09-28-2016, 11:48 PM   #51
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Quote:
Originally Posted by Dweezil View Post
I have 17k miles on mine. Have about 20 hrs of track time on them (sorry this isn't DD only OP). The wear sensors began to show signs of significant "wear" indicating they "need replacement". I will say that the rotor surface did not show any signs of wear however and the braking performance on street as well as track remained flawless and very desirable. Given that I track this car and don't have a lot of interest in spending 10-12k on replacement I decided to convert to iron rotors. I chose the Racing Brake conversion rotors and have bought both their track and street pads. I have so far run the track pads and plan on running street soon. I will leave a review of my experience on the rotors and pads

But back to OP inquiry about DD, I have a friend with CCB that does no track days at 20k miles and there is no sign of wear on the sensors as I have found on mine.
Can you please provide some info on the iron replacements?
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      09-29-2016, 08:58 AM   #52
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Originally Posted by adc View Post
Can you please provide some info on the iron replacements?
http://www.racingbrake.com/RB-2pc-Ro...bmw-irk-11.htm
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      09-29-2016, 09:00 AM   #53
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I believe the consensus was that if your not tracking the car, then the CCB rotors will likely last forever.

It only starts to get really expensive if you are running them on the track.
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      09-29-2016, 09:20 PM   #54
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[QUOTE=evanevery;20634694]I believe the consensus was that if your not tracking the car, then the CCB rotors will likely last forever.

It only starts to get really expensive if you are running them on the track


Agreed
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      09-30-2016, 08:38 AM   #55
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Update: My scale arrived the other day and I re-weighed the front rotors that my BMW SC removed:

LF old rotor shop weight: 7350g (min 7215g)
My weight: 7348g

RF old rotor shop weight: 7363g (min 7224g)
My weight: 7357g

So, both of those measurements are withing 5g. Both scales are reading pretty similarly. Less than a tenth of a percent difference (0.07 %). This would likely indicate that these weights are pretty accurate.

My next step is to thoroughly wash/clean/dry each rotor and reweigh them to ensure no debris is artificially adding to the rotor weight.

BTW - The scale I am using is relatively inexpensive ($30), has a 10KG capacity, reads down to the individual gram, and also appears to be pretty accurate: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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      10-02-2016, 06:30 AM   #56
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Great detail. Second measurement is confidence builder. After washing how will you dry completely? Maybe bake them in the oven at a low temp like 250F or could that damage them?
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      10-02-2016, 12:05 PM   #57
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Quote:
Originally Posted by shay2nak
I wasn't looking at maintenance cost, but longevity as a DD. I'd have to repeat above, since I haven't seen it, must not be any issues.
I had them on my M6 , even with FBO and tune AND 4 track days they were great at 26,000 miles hadn't even had to change the pads yet . Probably 80k miles on stock pads if just used on the street. Since the M3/4 are 600 lbs lighter and have much less power it certainly won't be worse than that .
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      10-04-2016, 11:44 PM   #58
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Quote:
Originally Posted by CanAutM3 View Post
You got me totally confused with that question ???

My understanding:

Wear sensors are to warn about pads needing replacement, they will sound an alarm in iDtive and are very accurate. They do NOT measure rotor life though.

There is an algorithm in the iDrive that estimates how many miles of life are remaining on the brakes based on driving style. It will sound an alarm in iDrive when it estimates the brakes need replacing. This is an estimate and is not accurate.

There are visual wear indicators on the CCB rotors. When they are half exposed, it means that the rotor likely need to be replaced. Those indicators are visual only and will not sound an alarm. The CCB rotors need to be weighed to accurately assess their life.

There you go
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      10-05-2016, 05:59 AM   #59
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Originally Posted by TheIceStormOf06 View Post

There you go
????
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      10-09-2016, 03:28 PM   #60
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Maintenance of CCBs is an issue of interest, as I have an opportunity to purchase a preowned M3 with CCBs. Over 12k miles, very well optioned, daily driver, no tracking or winter driving. Feedback from actual owners on maintenance, servicing, cost, warranty coverage would be appreciated.

Thanks in advance.
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      10-09-2016, 11:00 PM   #61
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Quote:
Originally Posted by Full Court Press
Maintenance of CCBs is an issue of interest, as I have an opportunity to purchase a preowned M3 with CCBs. Over 12k miles, very well optioned, daily driver, no tracking or winter driving. Feedback from actual owners on maintenance, servicing, cost, warranty coverage would be appreciated.

Thanks in advance.
Same here, was working on a lease takeover of a 2015 with CCBs when thread started. Lots of great info already posted.
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      10-12-2016, 01:43 PM   #62
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CCB rotors and weight loss:

CCB rotors are a composite material of carbon and ceramic (a few other things too but lets not complicate things here). An analogy (maybe good, maybe not so good) is rebarred concrete. Concrete is the ceramic and the rebar is the carbon.

If you lose too much carbon (from the rotor getting hot and the carbon oxidizing - fancy word for burning), your composite becomes a single material rather than a composite of 2 materials.

Rebarred concrete is much stronger, resilient and such than plain concrete.

Lose too much carbon from your CCB rotor and material failure (cracking, shattering etc) becomes more likely during regular use. Under heavy braking, the rotors experience tremendous forces....and being a bit weak after having too much carbon burnt off can lead to rotor failure. Like most ceramic materials, the failure under heavy load is likely to be catastrophic - like the whole rotor disintegrating into many many pieces.

Don't use a CCB rotor past its useful life.
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      10-14-2016, 07:16 PM   #63
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Quote:
Originally Posted by evanevery View Post
Update: My scale arrived the other day and I re-weighed the front rotors that my BMW SC removed:

LF old rotor shop weight: 7350g (min 7215g)
My weight: 7348g

RF old rotor shop weight: 7363g (min 7224g)
My weight: 7357g

So, both of those measurements are withing 5g. Both scales are reading pretty similarly. Less than a tenth of a percent difference (0.07 %). This would likely indicate that these weights are pretty accurate.

My next step is to thoroughly wash/clean/dry each rotor and reweigh them to ensure no debris is artificially adding to the rotor weight.

BTW - The scale I am using is relatively inexpensive ($30), has a 10KG capacity, reads down to the individual gram, and also appears to be pretty accurate: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
CLIFF NOTES*: By estimation, new F8x front disc should weigh approx 95 grams over the Minimum Weight; rear disc approx +40 grams. Min Weight is specific to each individual disc due to the >95% hand-made manufacturing requirements.

*As soon as the detailed service spec tolerances for F8x MCCB are made available, this will be corrected as needed and official PDF made available.

I don't doubt the the weights you've been given nor the weights measured with your own scale. What I do have a very difficult time accepting is the accuracy of the scales and the impact of contaminants remaining on the rotor when assessing a used CCB disc. My estimates earlier in the thread were based on calculations using known parameters for other CCB systems, specifically the M5/6 system, which is the closest in design and materials to the M3/4 system. The M5/6 discs are slightly larger in diameter and equal in thickness both front and rear. The larger diameter will have a slightly higher allowable weight loss, however thickness has a much larger impact on the percentage of allowable loss of the total disc weight. Knowing the M5/6 have a maximum loss of 100g Front and 70g rear, the M3/4 CCB discs will be less or equal to due to their smaller diameter. They will not be greater than in any circumstance. The annulus dimensions for both types are known, allowing an acceptable estimate in total weight differences imposed by the different disc hats including the incorporated parking brake drum on the M3/4. The only remaining unknown variable is vane count and vent area width. Applying some maths to all this gives an estimated maximum allowable loss of 96g Front and 41g Rear if the vent stricture is in proportion to the diameter difference. For added measure, I had one of my employees go dig out a front and rear rotor from my M5 and measure the weight on a TÜV Certified Scale calibrated with 8kg prior to weighing. The discs had a couple hundred miles on them when removed and were steam blasted to remove all residue without saturating the discs. The front came in at 99.90g over min specified weight with the rear at 70.05g over. My F8x estimates are unlikely to be the exact figures once an updated service bulletin for F8x CCB is produced, but based on my experience with multiple types of CCB for street, competition, and aviation purposes; erring to the side of caution, I would not hesitate using them to assess the discs on my own or a loved one's car. 200g difference just isn't in the ballpark...not even with 5x's the max manufacturing tolerance and the safety overage added on top. My remarks are not meant to infer personal negativity towards you, anyone with MCCB, nor an attempt to imply any incompetence or wrongdoing. Unfortunately it's inevitable that some will take personal offense simply because the topic concerns a personal purchase decision already made.

The ambiguity and intentionally confusing marketing statements from BMW (almost all OEMs TBH sans McLaren and Ferrari) that is utilized to sell a rather expensive upgrade to consumers least likely to utilize any meaningful benefits, the lack of easily obtainable and correct reference information regarding service life and fitness for use when it comes to this specific type of Carbon Ceramic Composite Brake System compared to all the types available, gives reason to take time and actually produce a resource based not only on manufacturers specs but on real world experiences as well. Carbon Composite Brakes don't qualify as new tech anymore, but they are only now becoming common tech. There isn't a vast amount of factually correct knowledge and much of it hard to find. Hopefully this thread and a few others can assist our fellow enthusiasts before choosing to commit to the upgrade. Blanket statements for or against MCCB serve no purpose, but guidance based on intended use will unquestionably determine what is a very wise or a very poor choice. The marketing fluff, myths, often incorrect speculation and amateur advice is far too rampant. For more spirited drivers/those who plan to or do more than 1 track event, already have MCCB, and want to explore aftermarket options to best suit the use and budget can find that as well...all in one easy to find, easy to read, anyone can understand thread.

One thing I feel this thread will expose very soon to BMW, if it hasn't done so already, is a likely flaw in the existing service procedures, training of these, and the guarantee that suitable assessment equipment is always available and used. It does not benefit them, or any other OEM, to produce parts well in excess of their service spec requirements nor depend on and maintain a service network unable to appropriately determine a critical component's condition. The negative financial impact on the manufacturing side makes that scenario improbable and liability exposure during use too great for an issue to be ignored of one does exist.

The only two assessment methods with 100% accuracy are the visible wear indicators and the Carboteq Proteq Tool. Wear on all CCB types is determined by both Minumum Weight AND Minimum Thickness in relationship to each other. The primary visual characteristics ARE significantly different depending on the disc type. In ideal circumstances, the abrasive wear and oxidative wear is linear. At the Specific Minimum Thickness, the weight should equal the Specific Minimum Weight. Because perfection is a theory at best, moisture/other environmental factors cannot be avoided, and every disc will exceed 500c at least once in its life, one Minimum Limit will be reached before the other. For the current BMW CCB system, the difference between Thickness New and Minimum Allowable Thickness is unbelievably small (40 microns each inside/outside certified limit; 50 microns complete surface loss) and does not impact the calculated weight in an easily measurable amount. For the weight assessment, it's a calculated figure to represent loss in specific density (mass) of the disc. Mass doesn't change with gravity but we aren't in space and gravitational influence varies with geography making mass a bit of a challenge to measure accurately. Someone else experienced in Thermodynamics can provide the correct terms for a container that may minutely decrease in volume while the contents within lose density, with both occurring and only one or the other occurring independent or simultaneously (head exploding).

Given the very small units the allowable changes are measured in and at very small amounts, it's easy to botch an assessment without highly accurate tools. The Proteq tool eliminates the variables and displays the true density and volume remaining. The corresponding minimums are marked on the hat for reference and have ZERO allowable tolerance, hence the very expensive price tag for the kit. I have 1 back in hand, a second on the way from my other office overseas, and trying to make a few more available early next year. My aim is to have one available within a reasonable distance to the most frequently used HPDE Tracks first, followed by another plan with increased access if the need remains.

I see another growing concern that truly gets to me on a personal level and hasn't been a topic of discussion more than a handful of times. Used MCCB kits are showing up for sale with increasing frequency and the vast majority of them are in dangerously poor condition. Components that are in good condition are out there but require careful packaging and protection during shipment. Wherever the info is sticky'd, I'll post a PDF Guide that can be used by both vendors, private sellers, and interested buyers for used MCCB components.

Quote:
Originally Posted by Full Court Press View Post
Maintenance of CCBs is an issue of interest, as I have an opportunity to purchase a preowned M3 with CCBs. Over 12k miles, very well optioned, daily driver, no tracking or winter driving. Feedback from actual owners on maintenance, servicing, cost, warranty coverage would be appreciated.

Thanks in advance.
Quote:
Originally Posted by IB M View Post
Same here, was working on a lease takeover of a 2015 with CCBs when thread started. Lots of great info already posted.
For the two members above, an MCCB equipped car used for normal daily driving and washed with proper cleaning methods should only need pads every 40k miles and rotors every 80k miles. If pads are replaced at 50% worn rather than 70%, the disc life can potentially exceed 100k miles. Pads are not "cheap" but discs are 1000x more expensive. A small insurance cost against an expensive maintenance item for someone keeping the car for a long time or accumulating high miles is well worth it. Proper cleaning means nothing more than a light mist of water, a wash-mit with minimal amount of ph neutral soap, and a light rinse. Chemical wheel cleaners, foaming, and excessive water saturation the potential lifespan of both the pads and rotors. Ideally a small home kettle pressure steamer is perfect and most effective.

Some companies claim the ability to refurbish BMW MCCB Discs. This is physically impossible to do and such services or purchase of refurbished discs should never be done. Currently there are no specific regulations for Carbon Ceramic Brakes vs Conventional Metallic Brake Components on any level. This will change during the first half of 2017.

Quote:
Originally Posted by Woodengun View Post
CCB rotors and weight loss:

CCB rotors are a composite material of carbon and ceramic (a few other things too but lets not complicate things here). An analogy (maybe good, maybe not so good) is rebarred concrete. Concrete is the ceramic and the rebar is the carbon.

If you lose too much carbon (from the rotor getting hot and the carbon oxidizing - fancy word for burning), your composite becomes a single material rather than a composite of 2 materials.

Rebarred concrete is much stronger, resilient and such than plain concrete.

Lose too much carbon from your CCB rotor and material failure (cracking, shattering etc) becomes more likely during regular use. Under heavy braking, the rotors experience tremendous forces....and being a bit weak after having too much carbon burnt off can lead to rotor failure. Like most ceramic materials, the failure under heavy load is likely to be catastrophic - like the whole rotor disintegrating into many many pieces.

Don't use a CCB rotor past its useful life.
If I may elaborate on that analogy a bit, the carbon fibers are the rebar, the Carbonized Silicone is the Aggregate, and the ceramic composite the mortar mix. Lose enough of either of the first two and it's like trying to make a multistory building structure with unsanded grout.

This vid below is an F1 Carbon-Carbon Disc run to the fiber loss limit with a maximum deceleration demand applied past the threshold. The disc explodes at 900c, which then causes the newly exposed fibers to instantly oxidize causing thermal runaway. At 1300c the carbon fully ignites. Although this is almost impossible to achieve on the street and quite difficult to incite on most tracks, it can and has occurred with Street Oriented Discs subjected to track abuse. Sebring or Hockenheim on a hot summer day and a driver with not so good braking skills will easily reach 850c. Pads will usually stop functioning at that point but they aren't tested above 800c. If a disc goes below its wear limit and remains in stressful use, the results can be quite dramatic.

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      10-15-2016, 08:56 AM   #64
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Quote:
Originally Posted by lemetier View Post
CLIFF NOTES*: By estimation, new F8x front disc should weigh approx 95 grams over the Minimum Weight; rear disc approx +40 grams. Min Weight is specific to each individual disc due to the >95% hand-made manufacturing requirements.

200g difference just isn't in the ballpark...not even with 5x's the max manufacturing tolerance and the safety overage added on top.

New Rotor Info (Weight New - Min Weight = Usable Weight):
LF: 7356g - 7165g = 191g
RF: 7294g - 7096g = 198g

Is it really possible the PDC shop scale could be off by that much?
You estimate front rotors should only have around 95g over min and that 100g discrepancy is all due to an inaccurate scale?


I'm no expert at all, and I don't mean this question to be taken as condescending, I'm asking out of genuine curiosity
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      10-15-2016, 09:27 AM   #65
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Quote:
Originally Posted by LDSM
Quote:
Originally Posted by lemetier View Post
CLIFF NOTES*: By estimation, new F8x front disc should weigh approx 95 grams over the Minimum Weight; rear disc approx +40 grams. Min Weight is specific to each individual disc due to the >95% hand-made manufacturing requirements.

200g difference just isn't in the ballpark...not even with 5x's the max manufacturing tolerance and the safety overage added on top.

New Rotor Info (Weight New - Min Weight = Usable Weight):
LF: 7356g - 7165g = 191g
RF: 7294g - 7096g = 198g

Is it really possible the PDC shop scale could be off by that much?
You estimate front rotors should only have around 95g over min and that 100g discrepancy is all due to an inaccurate scale?


I'm no expert at all, and I don't mean this question to be taken as condescending, I'm asking out of genuine curiosity
I admit it can seem to be an extreme discrepancy at face value. When the unit of measurement is included, it becomes a bit more understandable. It's 1% of the total disc weight...a little less than 15 quarters. Everyone has access to currency coins and their weight is accurate as long as long as they're relatively fresh. If evanevery doesn't mind taking a few minutes and puts one of the rotors on his scale and then adds 5 quarters, one at a time, followed by another 5 all at once and notes the change, the sensitivity and accuracy can be better judged. Each one is 5.67g.

I'd actually be relieved to be wrong in a way but a bit disappointed at the same time. If there really is double the minimum mass there, people are being ripped off for large sums of money on premature replacements. I just have never seen a disc weigh in more than a tiny amount over the allowable weight loss. I think the forum sponsors specializing in brakes will agree and have seen the same.
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      10-18-2016, 10:40 AM   #66
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I'm sorry, but I'm going to go with the accuracy of the "local" scales as being pretty good. The fact that they both (BMW SC scale and my Scale) weigh very close to each other is pretty indicative of this fact. I don't feel it necessary to have to weigh additional coinage to satisfy this finding.

I really don't have any way to check/compare the accuracy of the PDC scale though.

Additionally, The M5/M6 and the M3/M4 CCB's ***ARE*** different. They have different dimensions and may be subject to some sub-generational design and/or compositional changes as well. The trick is finding out what the starting mass of the rotors is. I think the numbers I have calculated are reasonably close. I don't think there is anything magical about how the "min" weight is calculated. I thoroughly expect that the min allowable weight is simply the starting weight minus some allowable loss. It is the allowable loss which will help us determine how far into a rotor we are by comparing its current weight vs the min allowable weight. There is, in fact, a document which specifically identifies the allowable loss for the M5 CCB's - but unfortunately NOT the M3/M4 discs. So barring this info from BMW, we must calculate that value and it should be as easy as comparing the weight of a fresh disc vs its stamped min weight.

Also, The wear indicators are NOT a particularly gtood method to determine rotor wear. In fact, the CCB docs state that the wear indicators are used to simply indicate when it is time to remove the rotor and actually weigh it. They are only visual wear indicators and NOT the final deciding factor.

I'm in the process of purchasing a Carboteq instrument. It really is the only way to acurately determine the wear state of CCB rotors. Even the min weight is merely an approximation and is subject to mechanical contamination (debris) and deterioration (chipping).

Based on the wieghts I see on my removed/used front rotors, I'm thinking I have about 60-70% life still left in them (by using the estimated allowable loss, current weight, and min allowable weight). Once I get the Carboteq, it will be pretty easy to see how close this estimates are. (The discs are stamped with a starting/min inductance measurement in three places on each rotor).

I'll be sure to post my findings in this thread once I get the Carboteq...
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