Various Ceramic Brakes on eBay

[IanH755]

Hi All,

Just scanning eBay etc and seen these for sale -

http://www.ebay.co.uk/itm/BENTLEY-ceram ... Sw~AVYtuTP

The caliper says "Bentley" (obviously) but these are the same discs, ***calipers etc as the RS6, just with a different paint job*** (Info incorrect, see Golfather reply below). The advert says the rear disc has a chip so I'd want to see that before bidding as ceramics are a write off if chipped (No "cosmetic damage") but a rear disc is under £1k if you want to try and chip the price down further.

I also found these from Germany, both bits from the same seller (mileage/wear maybe a bit high)

Rear Kit - http://www.ebay.co.uk/itm/Audi-RS6-4F-K ... SwUgdZdLnN
Front Kit - http://www.ebay.co.uk/itm/Audi-RS6-4F-V ... SwwyFZdLwf

I'm nothing to do the sellers, just thought I'd post what I've found.

[kent_andy]

I thought a chipped disc could be rebuilt via that Germany company? About a grand from memory?

[IanH755]

IIRC when rtd asked them about it they don't provide the service anymore (or something similar) which meant a rebuild was a no-go.

[daytonamart]

From what you can see the front right is the chipped one on the Bentley ones and it looks pretty severe to my eyes.

[Golfather]

Discs are shared between RS6 and Bentley but the calipers are different.
They may still fit but have smaller pistons and seals.

[IanH755]

Good Info there Golf, thanks!

[douglas96]

Discs are shared between RS6 and Bentley but the calipers are different.
They may still fit but have smaller pistons and seals.

The information in this post is incorrect - see FUBAR's post and my response to his post.

I would be careful if fitting the Bentley calipers in that case - if the pistons in the caliper are smaller than the original Audi ones then the pressure at the calipers will increase - leading to the possibility of blowing seals, hoses and the brake pedal being too "sensitive". If you were going down the route of changing to calipers with smaller pistons in them, it would be best to check for differences between the Audi and the Bentley master cylinders to see if they are compatible or have different bores, etc.

[douglas96]

It appears that the brake master cylinder on the C6 RS6 is used on quite a few Audi models including the C5 platform of A6 and RS6 and the B7 A4 and RS4 platforms. The part number appears to be "4B3 611 021" and is made by "TRW GIRLING". From information found on the internet the bore of the cylinder is listed as 27mm. Unfortunately I can't find any Bentley parts drawings online (one website seems to have the drawings however won't allow me to view them unless I subscribe) to find the part number for the master cylinder that the Continental uses.

[FUBAR]

Discs are shared between RS6 and Bentley but the calipers are different.
They may still fit but have smaller pistons and seals.

I would be careful if fitting the Bentley calipers in that case - if the pistons in the caliper are smaller than the original Audi ones then the pressure at the calipers will increase - leading to the possibility of blowing seals, hoses and the brake pedal being too "sensitive". If you were going down the route of changing to calipers with smaller pistons in them, it would be best to check for differences between the Audi and the Bentley master cylinders to see if they are compatible or have different bores, etc.

Pressure will not change, the clamping force will decrease if the total piston area decreases or increase if the piston area increases compared to the Audi caliper. Don´t see why they would change the piston sizes, the Bentley has the same rear setup as the RS6.

[Golfather]

Bentley calipers use 28.6mm pistons and audi use 30.15mm
The pistons tend to seize on the ceramics as they are steel, and are not a listed part at Audi so you have to go direct to Alcon for spares - Alcon part number PSS3036X560
Bentley do supply the pistons separately - part number 3W0615403A
The pads are also different between the RS6 and the Bentley.

Infact the only thing shared on both setups and share the same 3W0 part number are the discs and the disc splash guards.

[douglas96]

Discs are shared between RS6 and Bentley but the calipers are different.
They may still fit but have smaller pistons and seals.

I would be careful if fitting the Bentley calipers in that case - if the pistons in the caliper are smaller than the original Audi ones then the pressure at the calipers will increase - leading to the possibility of blowing seals, hoses and the brake pedal being too "sensitive". If you were going down the route of changing to calipers with smaller pistons in them, it would be best to check for differences between the Audi and the Bentley master cylinders to see if they are compatible or have different bores, etc.

Pressure will not change, the clamping force will decrease if the total piston area decreases or increase if the piston area increases compared to the Audi caliper. Don´t see why they would change the piston sizes, the Bentley has the same rear setup as the RS6.

Hi Fubar,

Apologies - what I wrote is incorrect as you pointed out. You are correct that the pressure in the system will not change if the calipers are changed for ones with smaller pistons. The pressure is determined by the master cylinder diameter (smaller diameter = increase in pressure, bigger diameter = decrease in pressure). The only thing that has changed is clamping force.

And again, you're correct that increasing the caliper piston size will increase the clamping force. However this will result in increased pedal travel.

However I would still be careful if changing the calipers - check the master cylinder specs on the Bentley first.

Regarding the setup being different between the two cars, it is likely that the brake bias is different, possibly explaining the difference in caliper piston sizes.

Thanks for pointing that out - the reason for my previous train of thought was due to the time when I was considering upgrading the brakes on my car to those off a MKIV Volkswagen Golf R32 or what I preferred (if I could find a setup) to those off the B5.5 Volkswagen Passat W8. I was informed basically exactly what I wrote in my previous post - that if the piston size at the caliper was changed then the line pressure has changed, which I now know to be incorrect after reading up on the subject.