if anyone is interested. Racing Brake is willing to make custom rotors for a c300/450/43 rear caliper upgrade. They already have the front 2 piece for c43 and c63, you can upgrade your c300 or 400 to c63 brakes. most wont need this but i know some people like the look (a lot of money for looks but at least you can stop on a dime). With this upgrade, the front and rear would match and you can retain your factory fronts which are honestly ample for most people on here. I have only found them to be in adequate on faster tracking with higher speeds above 120mph.
My legwork with the c63 amg oem rear calipers shows they can be bolt on and plug and play. We need 5 guys to pre order these custom 2 piece rotors. for the upgrade all you will need are the oem c63 rear calipers. You can find them used or i can help you get them new. they run about $400 per new painted in red or the carbon ceramic color. and about $350 if you want the gray.
I do not have cost yet, but my guess based on the c63 offering would be around $1000-1100 for the pair. Remember these are 2 piece rotors!
If there is enough interest, we can also talk to them about machining a bracket to mount the c63 caliper to the front as well. they already have a rotor for the c63 for the front too.
PM me if interested and the setup you would be interested in.
I wanted to update the thread. I have the options for c63 brake upgrade for the c300/400/450/43.
I can post pics later of the c63 brakes mounted. Some issues with getting the c63 rotors to fit. our hubs are different than the 63 to accept our different rotors. I thought the geometry would work out but no dice.
There are 2 cheaper best paths forward. In both cases, the c63 calipers are bolt up using oem hardware.
1. I can buy 2 piece Brembo OE rotors for both front and rear. 390mmx36mm or 360mmx36mm for the front and 360x26mm for the rear. The 360mm setup fits under OEM 18" c43 front wheels the way i am designing it. All setups will clear any 19" wheel. They will all use oem c63 calipers in red or gray which will bolt on. I will be machining custom rotor hats and front brackets for the c43/450/400 and C300. They will bolt into the Brembo OE rotor friction surfaces using existing hardware. They will bolt onto your car. No other mods needed. estimated cost would be about $300 for these custom hats for front and rear. then you would need to buy the rotors which are about $350 per rotor new. or you can pay slightly more on FCP euro and get replacements for lifetime for the cost of shipping. so essentially lifetime brakes for about $1900. This is a few hundred dollars cheaper than the racing brake option with not much ongoing cost. and you get oe quality Brembo brakes.
2. We get a group buy of a few people to go to racing brake and they will make a custom rotor for the rear. The only issue i see is that the c63 rotor will not bolt up to the front without the mods i stated. Thus this option probably will only be a rear upgrade plus c43/450 front stock caliper. Cost for this if it follows thier online prices for the c63 will most likely run about $22-2400 usd for 4 rotors. They claim to have a better design than OEM and are lighter at the sacrifice of rotor wall thickness.
If anyone is interested in either option please let me know. I wanted to try to get a few people together to reduce start up cost.
My c63s brake upgrade is coming together for my 17 c43 brembo "OEM" 2 piece rotors and oem calipers. I will be using porterfield racing r4s pads . Still working out some clearance issues on the rear but i pretty much have everything figured now! Best part is it will clear some 18" wheels if you prefer. But i ended up upsizing winter tires and will run 19" wheels. If anyone is interested in getting this setup let me know. Not super cheap but performance is there. and as far as oem brembo upgrades go it is relatively cheap.
Just finished the rear and front c63s brake upgrade on a c43!
Rear takes sl65 black series rear rotors and you must modify the rotor hat. Unfortunately this upgrade will not work on c63 due to offset. sorry c63 guys. you would need to make a completely custom hat to use these brembo 2 piece rotors. These sl65 black series 2 piece rotor hats are steel oem to accommodate the drum parking brake on these older cars with mechanical parking brake. This is not needed on newer cars with electric parking brake. I also had to replace wiring, brake lines, and modify oem dust shield. But it all is pretty much bolt on and plug and play with c63s parts. You must run 19" wheels or special 18" to clear these brakes! for the front, i machined brackets and used oem dust shield. replaced brake hose with c63 hoses and everything else was bolt on for the 390mm rotors! these will only work with 19" wheels.
I am looking to get a group together to make these rear hats out of aluminium to save about 4 lbs per corner! You can just upgrade the rear brakes if you want the look but IMO the fronts being larger look great and perform great as well!
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brembo "OEM" 2 piece rotors and oem calipers. I will be using porterfield racing r4s pads 
