Picked up my 2015 C63S about three years ago — 220 mph on the dash, nearly mint when I got it. Had around 41k miles then, sitting at about 55k now. Over that time I’ve done quite a bit of maintenance and repairs: replaced rear struts, front control arms, rear axles, coolant flush, brake fluid flush, transmission oil change, brake pads, spark plugs, tires. Struts axels and control arms were replaced based on dry oil on struts, leaking cv boot and a squeaking passenger front control arm over light bumps (warranty replaced both sides). Most of it was done at the dealer under an extended warranty I bought with the car for about $3k / 2 years. Definitely paid off.


Back then, I mentioned to the dealer that I was feeling a slight slip on cold starts and suspected a wet clutch issue. They said they couldn’t properly diagnose it because I’m running wider wheels and tires (295/30/19 in the rear and 245/35/19 up front), and the readings wouldn’t be accurate. The issue on cold start still hasn’t changed since then. Some have said the slipping on cold start is normal due to oil pressure/temp etc but doubt that.

Right now I’m chasing both the wet clutch slip on cold start and a rear brake drag issue myself. Once, in the last three years, the car almost stalled on a cold start as I was slowing down to a stop sign — it felt like it was about to shut off right before coming to a complete stop. Since then I changed the spark plugs and not sure if it would be related anyway.



Rear brakes drag only when warmed up but not cold. I already did a full brake flush and bleed. Next step is to drive it, jack it up, pull the wheel, and crack the bleeder. If fluid shoots out under pressure, it’s probably a hose or upstream pressure issue I guess? If not, it’s likely the caliper piston not retracting properly. Has anyone been successful with it just being the hose, or having to rebuild the caliper, or it being the brake actuator? How do you really diagnose if the actuator is not retracting properly?



Any input or advice from anyone who’s dealt with this on a W205 C63S would be much appreciated. Car drives great other than listed problems.



Also side note 🗒️ I’m looking to get another warranty if anyone has positive experience with one. They would have to pay $250/hr shop rate like my last warranty covered. Thanks 🙏 💪

 

Slip with the old 7-speed MCT is something that I've read before. Car doesn't have a lot of miles, though, for the clutch to be worn already, but who knows how many Race Start launches this transmission has done over the years. What do you mean by 220 mph on the dash? Certainly sounds like something's going on, though if you also have RPM fluctuations. Brake drag won't help, so that's probably the first thing to get resolved. The rear calipers are sliding calipers, so one of your calipers is likely stuck and doesn't slide anymore.

 

Ok so the dash tops out at 220 mph not 200. Not sure why. The rpm fluctuation only happened one time on cold start approaching the stop sign and seemed to either be spark plugs (prob not but never happened more than once) or wet clutch not disengaging properly when cold or something.

for the rear caliper I took apart the sliding pins cleaned up all the silicone lube to prevent too much grease preventing slide pins from moving. That wasn’t it. At least I don’t think. I also cleaned under the shims and the under the bracket. Pads and calipers slide fine. Then I did a brake fluid flush. Didn’t prevent the brake drag. So today I’m going to take the car for a test drive and when hot crack the bleeder and see if any pressure is built up. At this point I’m thinking it’s either the caliper/hose/or master cylinder.

regarding the wet clutch on cold start. After the clutch moves it works fine but definitely takes the car warmed up to get the car moving normally. Some people on this form said it’s normal and others have gotten it replaced and symptoms went away?

it’s a beautiful car drives great just a couple of issues. I’d hate to not get these problems fixed because I’m thinking of keeping the car long term.

warranty would come in handy with the issues so I don’t have to spend so much at the dealer. I spent 1300 a week ago doing a brake flush ( abs valve bleeding process) coolant flush and spark plugs. Still dragging and wet clutch hasn’t been tackled yet.

I heard of Route 66 warranty but honestly always had dealer warranty. Fidelity warranty I seen someone mention is good but is only sold by the dealer. I called them yesterday.

thanks for the advice. Any advice how to diagnose the brake actuator being the issue? Parking brake is a possibility because it only drags when warmed up but no drag on cold start.

 

I don't know what the 220 vs 200 on the instrument panel has to do with your car issues... All the C63's I've seen have 200mph on the speedo. But now I'm curious... Post a pic of yours.

Transmission slippage when the car / fluid is cold is normal. When you had the transmission fluid changed did the dealer do it? Reason I ask is that the 7-speed MCT is pretty picky about its fluid level and type of fluid. There is a messy procedure to check the transmission fluid level where it is supposed to drip out of the tube at a specific rate. Maybe the dealer didn't fill it properly? Worth checking to be sure.

How do you know you have a rear brake dragging? If it was really dragging the rotor should be getting ridiculously hot as you drive it and you'd probably smell it and have heat marks on that rotor. When you took the caliper off did you have to pry it off, or pry the piston back in the caliper a little? If you were able to just pull it away from the rotor to service it, then it's not "hanging".

I also am a little concerned about your statement:The slide pins and caliper bores for the pins are supposed to be well lubed with a high temperature lube.

Also this is concerning:If your car is in park the automatic parking brake will be set and so there will be pressure back there and fluid WILL come out. You'd have to have the car in neutral, with the parking brake off, and then get under the car to crack the bleeder, which is dangerous unless you have the wheels chocked and your on a really flat surface. But fluid is still going to trickle out anyway so I'm not sure "cracking the bleeder" will tell you anything.

 

Yes, most w205s top out at 200 mph but mine tops out at 220 mph. I believe the governor was removed during build as well. Cold start slipping was happening prior to the dealer replacing trans fluid. Cold starts are still slipping after trans was serviced and yes was done by MB dealer. They filled it properly and people have stated that slipping on cold start went away after wet clutch was replaced but wanted to confirm this. If that's the case in my opinion its NOT normal for cold start slips unless replacing wet clutch doesn't fix this.

I know the rear brakes are dragging because they get hot after driving and is hotter than front rotors. Also, in neutral the car stops rolling freely on a slight hill and yes rotors are taking a beating. Glazed slightly and driver side is now producing an outer lip due to excessive dragging. I'm suspecting caliper is seizing under heat which is most likely scenario at this point.

Sliding pins are NOT supposed to be over lubed as this can cause pressure between the sliding pin and the end of bracket bore. Excessive lubricant will cause the pins not to move all the way down and prevent them from moving freely. So again, don't over lubricate sliding pins as its well-known this isn't good for full range of motion of pins. If you get away with it fine but it's not recommended to over lubricate slide pins as it can prevent full caliper movement or cause pins to back out slightly. Yes, I use Permatex silicone extreme brake parts lubricant, and I suggest you use the same.

Lastly to bleed the brakes or open the bleeder screw you do not have to remove the parking brake actuator. You need to retract the parking brake using a scan tool or follow diagnostic brake pad replacement window (hold and press ok and home on steering wheel). This will retract the parking brake and allow the caliper piston to be pushed in. If there is pressure in the system due to faulty abs valves, master cylinder or brake house theoretically due to possible residual pressure will be present and indicates an up-stream issue than localized in brake area. I have never tried this myself. Also, you should never have to get under the car for such a thing and not sure what you're describing. There is no reason to get under the car for something like this. Especially in the manner in which you described. Your description of working under a car is an unsafe way of doing so and unnecessary.

I do appreciate your "concern" lol but please if I said anything you disagree with, I'm willing to hear you out. Also, I will post a picture of the dash speedometer for you to see. Can't do it on my phone because picture is over 10 mb.

Also, if you have any recommendations to an extended warranty. Thank you

 

Sounds like you've got it all covered.

It sounds like you are asserting that Mercedes Benz / AMG removed the 180moh "governor" (for "S" cars) when they built your car and put in a special / different speedometer as some kind of "Easter egg" pointing to that special feature. That would be unique and interesting.

I would never suggest running the caliper pins dry, but I would definitely suggest more than a skim coating of grease. There are flat spots on the caliber pins that allow any excess grease in the end of the bore to squish over the end and fill the void that the flat spots create, not to mention there being room for excess grease to spill out into the dust boot. Most mechanics work the pin in and out and twist it around a little prior to assembly to evenly distribute the grease on the pin and bore and remove any excess. But, you do you though.

I wasn't suggesting removing the parking brake actuator motor. Just put the car in neutral and release the parking brake so the caliper piston isn't pushing on the pads so as to release any line pressure. You do it your way... Xentry, service menu, or whatever. The caliper piston would just have be in its resting, not-applied, position to test the theory you are chasing.

Not sure how you are going to get to the brake bleeder without basically being under the car. I suppose you could jack it up, remove the wheel, put the brakes in service mode, and then access the bleeder... That seems like it would take a little time though and not necessarily be the "hot test" you mentioned.

If you have a caliper piston stuck in the bore something went wrong, like excess water in the brake fluid caused rust, or someone over tightened the banjo bolt on the brake line connection causing the copper washers to crush and the banjo bolt to bottom out on the piston. Or I suppose you could have an ABS malfunction (kind of unlikely without a code coming up though) or a damaged hard line that's just dented / tight enough to not allow fluid pressure to bleed back when you let off the brake pedal.

I wish you good luck in figuring out your brake drag, that's not a very common issue across any brand.

 

Build sheet on my car states governor was removed. It was a special ordered/built and delivered to the customer. Speedometer is indeed 220 mph and not sure if this is stock or not, but it almost certainly looks like it.
I agree with most of what you're saying. Yes, wheel should be taken off before opening bleeder for multiple reasons and brake actuator doesn't need to be retracted to bleed brakes. Also, if you don't take off the wheel you risk brake fluid stripping paint on calipers and inside of rim if not cleaned with water properly. I drive the car very aggressively so I'm assuming I overheated the rear brakes or caliper sticking became worse after heat cycles. Over lubricating pins is just my opinion and should have a good amount just not too much.

Hot test theory is just to see if pressure is in the line after it drags and if caliper loosens after if any pressure is released. Just trying to localize the issue. Does anyone know how to test the brake actuator being an issue?

I appreciate all your advice. Thanks for the good luck.

below is the picture of the speedometer


220 mph on dash

 

So, I called my MB dealer and got quotes for parking brake actuator and brake caliper. Even with my %15 off they were asking for $700 a caliper and $400 an actuator. I found it for half the price online through a wholesale Mercedes parts dealer. Part number for brake caliper is a-2314230381 and 0481 for other side. Actuator is 1669065401 priced at $277 a side. Guy in parts mentioned that rear brake calipers are rarely ever replaced and the brake actuators are normally the issue.

Question: how to test brake actuator vs caliper? Is there anything I should know when replacing the brake actuator? Piston on caliper can get compressed and actuator does seem to be working. I'm having trouble knowing which one is most likely failing without guessing through symptoms.