01-13-2020, 06:13 AM | #155 | |
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01-13-2020, 03:00 PM | #157 |
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I saw something strange when I removed the wheel today. It seems that the cooling channels in the disc is very effective. You can see small dots in the dirt in the inside of the wheel. I guess that this is the air from the disc that do this pattern. Could that also also be the source of the noise? Like a round harmonica😁 |
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01-13-2020, 04:16 PM | #158 | |
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Asking the same question... Have you cleaned it off? Any difference? |
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01-13-2020, 04:55 PM | #159 | |
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I hope someone will be able to verify this theory. |
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HighlandPete6658.50 clausmoll65.50 |
01-13-2020, 05:20 PM | #160 | |
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Do you know what wheel size was tried that were quiet? 19" by any chance? |
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clausmoll65.50 |
01-13-2020, 05:23 PM | #161 | |
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It is a simple thing to try by any decent dealer. |
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01-13-2020, 11:40 PM | #162 | ||
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01-14-2020, 12:54 AM | #163 |
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My dealer doesn't really seem to listen to my suggestions anymore, so could someone else get the dealer to try the 19" wheel?
It would be crazy if its a combination of M-Sport brakes and 18" wheels! Just don't understand why it's not present on the Sedan then.. |
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01-14-2020, 02:00 AM | #164 | |
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Are we infact sure that there are sedans with 18" wheels and M-sport setup including breaks that DON'T suffer from this problem? |
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01-14-2020, 03:32 AM | #165 |
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There is another approach, if the dealers don't want to spend more time on the problem examples. See if dealers have demo touring models with 19" wheel sets and sport brakes.
If they are silent, builds the case to try a 19" wheel set, as part of the problem solving. The picture of the inner wheel, with what looks like evidence of a pulsing air flow, should also arouse BMW's interest. |
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01-14-2020, 03:37 AM | #166 | |
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01-14-2020, 03:46 AM | #167 |
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My thinking... I look at the picture and try and understand the reason for what appears like jets of air to the rim. Count the venting vanes in the disc, I wager they match the air pulse marks in the dirt on the rim.
As I see it.. the air flow through the disc is acting like a turbine, possibly restricting, even 'compressing' the air as it passes through the caliper housing. As the vanes reach the end of the caliper, the air pulses out into open space. The rim size could be restricting the flow and generating the sound track. May be a bit more to it, like the shape or rigidity of the backing plate, also involved in way the air is restricted and/or dispersed. |
01-14-2020, 03:56 AM | #168 | |
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01-14-2020, 04:21 AM | #169 |
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Another thought.
Looking at RealOEM, it appears the latest sport caliper (G20) is a different shape than the F30, looks like a longer 'wrapped' form. Could be relevant in the air build up in the restricted space. Incidentally I run 17" winter rims on my car, it also has 348x36 discs. So space is just as restricted. My wheels get filthy inside, never ever seen any marks, which indicate a strange air flow from the brakes. What is different, my calipers are the standard floating type, quite open in design, although only about 6mm clearance to the inner rim. BTW, I've got a Brembo 348x36 disc here in my office, it has 48 venting fins, 24+24. One solid, one slotted, alternating around the disc. Assuming the G21 discs are the same, we have 24 'inlets', I expect there are 24 marks in the dirt. |
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01-14-2020, 04:39 AM | #170 | |
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01-14-2020, 04:46 AM | #171 |
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Here's a way to temporarily eliminate the airflow. Not recommending anyone take it on, but I know I would.
Wrap the vented area with insulation tape, a couple of times around the disc, make sure its contained in the area between the disc faces. Try a careful drive, get to the speeds where there is normally a problem. Just don't brake hard and heat the discs too much. |
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01-14-2020, 05:10 AM | #172 | |
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Tempting... |
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01-14-2020, 06:43 AM | #174 |
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Okay - I did it. It took 20 minutes out of my lunch break.
There was no difference in the noise what so ever. But I do still suspect the calipers/brake plate/wheel size theory. Last edited by clausmoll; 01-14-2020 at 06:49 AM.. |
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01-14-2020, 06:53 AM | #175 | |
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At least the test eliminates it being directly related to 'generated' airflow from the disc/caliper combination. I agree there could still be an issue due to something about the complete assembly. Trying 19" wheels has to be specifically tested, it is a process of elimination. |
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clausmoll65.50 |
01-14-2020, 06:56 AM | #176 | |
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I agree! |
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