CS Owners: What Are These???

[Kief]

Was just swapping out my wheels for my winters, and found these "spacer-like" very thin metal discs on my two front hubs. Have no idea what they are. This is my 4th F8x and I have never seen these before. They were only adhered to the hub face by the wheel (my wheel pin is the only reason they didn't fall to the ground when I removed my front wheels). If I tried to place back, they would move and block the lug holes as I tried to mount my winter wheel. I gave up and kept them off.

Is my car going to blow up (joking), but seriously, anyone know what they are? Were they mistakenly left on at the factory?? CanAutM3 help...

[tom @ eas]

BMW calls it a "friction disc":

[Kief]

Originally Posted by tom @ eas

BMW calls it a "friction disc":

tom @ eas Thanks Tom for the quick reply...do I need them? Or better yet, any advice on how can i keep them in place when remounting the wheel?

[kevin @ eas]

Originally Posted by Kief

tom @ eas Thanks Tom for the quick reply...do I need them? Or better yet, any advice on how can i keep them in place when remounting the wheel?

Found this on the internet

Genuine Bmw Disc For Higher Coefficient - 31108053073. This ring fits between the wheel hub and the backside of the brake rotor hat and prevents the rotor from shifting on the hub. If your F8X M3/M4 has a clicking noise coming from the front axle, especially when turning, BMW may have installed this ring to prevent excessive movement of the brake disc on the hub (per SI B34 05 15)

[Kief]

Originally Posted by kevin @ eas

Found this on the internet

Interesting...so this looks to be related to a SIB?
Because my previous 2018 M3ZCP 8/8/17 production did not have these discs

[Kief]

Originally Posted by kevin @ eas

Found this on the internet

Any ideas how to keep the disc in place as you remount the wheel?
The disc will move as you position the wheel to align with the lug holes, blocking the damn holes

[yjypm]

Originally Posted by Kief

Any ideas how to keep the disc in place as you remount the wheel?
The disc will move as you position the wheel to align with the lug holes, blocking the damn holes

Use two wheel pins. I found using two makes it a lot easier to position the wheel too.

[CanAutM3]

As others have posted these are "friction discs" that seem unique to the CS. Their purpose is not 100% clear. I doubt it is to prevent movement between the hub and disc since the disc is fitted between the wheel and disc. If anything, it is to limit movement between wheel and rotor, maybe due to the higher grip of the PSC2 tires under braking. Since I swap wheels quite often, I have taken them off my car.

[Kief]

Originally Posted by yjypm

Use two wheel pins. I found using two makes it a lot easier to position the wheel too.

That's a good idea...you have these discs too? Do have a CS or another F8x?

[Kief]

Originally Posted by CanAutM3

As others have posted these are "friction discs" that seem unique to the CS. Their purpose is not 100% clear. I doubt it is to prevent movement between the hub and disc since the disc is fitted between the wheel and disc. Since I swap wheels quite often, I have taken them off my car.

THAT'S ALL I NEEDED TO HEAR!!
If CanAutM3 doesn't use them, hell if I will!! Haha
I can sleep easy now tonight

[yjypm]

Originally Posted by Kief

That's a good idea...you have these discs too? Do have a CS or another F8x?

No I have a MY18 M3 ZCP and I have never heard the noise

[tom @ eas]

Originally Posted by CanAutM3

As others have posted these are "friction discs" that seem unique to the CS. Their purpose is not 100% clear. I doubt it is to prevent movement between the hub and disc since the disc is fitted between the wheel and disc. If anything, it is to limit movement between wheel and rotor, maybe due to the higher grip of the PSC2 tires under braking. Since I swap wheels quite often, I have taken them off my car.

Not unique to CS according to RealOEM.

We've had 2 CSs here, no discs installed nor have seen them on any other applications.

31108053073
Disc for higher coefficient of friction

Part 31108053073 was found on the following vehicles:

3' F80 M3   (04/2012 — 06/2015)
3' F80 M3 LCI   (01/2015 — 08/2018)
4' F82 M4   (02/2013 — 02/2017)
4' F82 M4 LCI   (05/2016 — 08/2018)
4' F83 M4   (06/2013 — 02/2017)
4' F83 M4 LCI   (05/2016 — 08/2018)
5' F10   (01/2009 — 10/2016)
5' F10 LCI   (08/2012 — 10/2016)

http://www.realoem.com/bmw/enUS/part...&q=31108053073

[Kief]

Originally Posted by tom @ eas

Not unique to CS according to RealOEM.

We've had 2 CSs here, no discs installed nor have seen them on any other applications.

http://www.realoem.com/bmw/enUS/part...;q=31108053073

And the plot thickens...
Nevertheless, I feel better with everyone's input and having not reinstalled them.
Thanks

[r0wr]

Originally Posted by CanAutM3

As others have posted these are "friction discs" that seem unique to the CS. Their purpose is not 100% clear. I doubt it is to prevent movement between the hub and disc since the disc is fitted between the wheel and disc. If anything, it is to limit movement between wheel and rotor, maybe due to the higher grip of the PSC2 tires under braking. Since I swap wheels quite often, I have taken them off my car.

I had these disc on my 2015 F82 so I don't think it's unique to CS

[CanAutM3]

Originally Posted by tom @ eas

Not unique to CS according to RealOEM.

We've had 2 CSs here, no discs installed nor have seen them on any other applications.



http://www.realoem.com/bmw/enUS/part...&q=31108053073

IIRC, when these friction discs were "first discovered" on the BMW ETK, they only showed on the M4cs and not on the regular M3/4 nor on the M3cs. It seems BMW have now widespread their use.

EDIT: I just re-checked the ETK, and when you look-up an M3 or M4, the pictogram shows the friction disc, but the part is still not listed in the parts list.

BMW has made even further changes where it now shows the 2 friction disc installed in the PUMA, one between the hub and the brake rotor and one between the brake rotor and the wheel. It seems that those discs come on the CS from the factory, but are listed as also available for other models, potentially to fix a particular issue under a service bulletin.

[Suds]

A very thin layer of grease act great as an adhesive.

Use a high temp, it will squeeze out when the wheel is torqued.

[CanAutM3]

Originally Posted by Suds

A very thin layer of grease act great as an adhesive.

Use a high temp, it will squeeze out when the wheel is torqued.

Euh, nope. Grease is a lubricant...

[gunsmoker]

Originally Posted by r0wr

I had these disc on my 2015 F82 so I don't think it's unique to CS

It's not a CS thing.
I had a creaking noise when turning and my dealer tried these, but they did not help. The installation procedure also requires sanding the rotor and the hub with a specific grit sandpaper. In my case the culprit ended up a play in the knuckle assembly where the strut is attached to the hub. They changed that clamp bolt and cleaned up the knuckle.

Wrt to the friction disks, due to the suspension stiffness and geometry, turning causes a lot of pressure on the hub assembly. You can see how the front end of the car raises up as you wind up the steering wheel. The disks create extra friction between the hub, the rotor, and the wheel to prevent a slight slippage that makes a creaking noise. There has to be one disk on each side of the rotor.

[Kief]

Originally Posted by gunsmoker

It's not a CS thing.
I had a creaking noise when turning and my dealer tried these, but they did not help. The installation procedure also requires sanding the rotor and the hub with a specific grit sandpaper. In my case the culprit ended up a play in the knuckle assembly where the strut is attached to the hub. They changed that clamp bolt and cleaned up the knuckle.

Wrt to the friction disks, due to the suspension stiffness and geometry, turning causes a lot of pressure on the hub assembly. You can see how the front end of the car raises up as you wind up the steering wheel. The disks create extra friction between the hub, the rotor, and the wheel to prevent a slight slippage that makes a creaking noise. There has to be one disk on each side of the rotor.

Then why doesn't every F8x come with them?
Like I mentioned earlier, my CS is my 4th F8x, and this is the first I'm seeing these discs. And others have confirmed never seeing these discs either.

[Suds]

Originally Posted by CanAutM3

Euh, nope. Grease is a lubricant...

Grease is sticky!!

We use this as an adhesive all the time.

[CanAutM3]

Originally Posted by Suds

Grease is sticky!!

We use this as an adhesive all the time.

In the sense that is a thick paste, yes it can provide a low force grip to keep parts together. But as soon as you start to apply greater forces, it acts as a lubricant. Apply grease between the wheel and hub interface will reduce the shear resistance.

[CanAutM3]

Originally Posted by r0wr

I had these disc on my 2015 F82 so I don't think it's unique to CS

I doubt it came from the factory that way, because these friction discs were not listed on the BMW parts catalogue before about a year and a half ago.