C63 BS soft brake pedal
03-11-2015, 09:22 PM
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C63 Black Series
C63 BS soft brake pedal
Hello. I got a full service for my BS in dec which includes a full brake fluid flush but 2 weeks ago the brake pedal started to be extremely soft. Previously, the brake pedal was nice and firm at the top. But now the ABS kicks in when I brake slightly harder than casual braking which is a bit alarming.
The car has only 15,000km on the clock and never been on to the track. I brought the car to a workshop and got them to rebleed and check for leaks but all is good. The brake pedal still remains soft with all the power at the bottom of the travel.
What should I do.. sigh
The car has only 15,000km on the clock and never been on to the track. I brought the car to a workshop and got them to rebleed and check for leaks but all is good. The brake pedal still remains soft with all the power at the bottom of the travel.
What should I do.. sigh
Last edited by prodigue; 03-11-2015 at 09:24 PM.
03-11-2015, 10:52 PM
#2
I have Motiv bleeder but I prefer to flush/bleed regularly with a full L of fluid via the gravity bleeding method. I tap each caliper with a rubber hammer and get even the tiniest bubble out. That done, the pedal is never as firm and high as I expect or hope for. Generally, I'd characterize the brake feel as only acceptable, nothing better than that.
03-13-2015, 07:15 AM
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W204 C63 Coupe, W166 ML350 BlueTEC, 928GT, C5 Z06 & IS300 race cars, EQE 4Matic+ on order
Had the same experience after a brake flush on my C63 coupe. Initially I also thought there was a bubble or two in the system, but then I myself went through another two liters of brake fluid - that's more than enough for a full flush - bleeding all four calipers looking for the culprit (been doing it on my track cars for 15 years) and there wasn't a trace of air anywhere. Apparenty the fresh MB brake fluid they use has a somewhat lower specific gravity at first so it takes less pedal pressure for the calipers to exert the same clamping force on the rotors (the ABS kicking in on your car confirms that you are in fact braking with full force). The pedal feel gets slightly stiffer over time. Shop foreman - a die-hard racer, not just a track junkie - confirmed this. In other words, the brake system works perfectly - it's just the pedal feel that has changed, and it will get stiffer again once it absorbs some moisture. Give it another couple of weeks.
BTW, the MB brake fluid is excellent in all regards - it has a higher boiling point than ATE SuperBlue, Type 200 or the MOTUL stuff and is way less hygroscopic. I - and half of the PCA track junkies - am/are now running MB DOT4 brake fluid in our track cars.
BTW, the MB brake fluid is excellent in all regards - it has a higher boiling point than ATE SuperBlue, Type 200 or the MOTUL stuff and is way less hygroscopic. I - and half of the PCA track junkies - am/are now running MB DOT4 brake fluid in our track cars.
03-16-2015, 02:21 AM
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Diablolis, thanks for the interesting insight.
It has been >3 months since the brake fluid was changed at the dealer so there has been more than enough time for the system to "absorb moisture" according to your explanation. And the situation only got worse the past 2 weeks.
Tapping to brake at low speeds is acceptable, but you can really feel the pedal sink down with less than adequate braking power while stepping on it to slow down at higher speeds (>80kmh).
It has been >3 months since the brake fluid was changed at the dealer so there has been more than enough time for the system to "absorb moisture" according to your explanation. And the situation only got worse the past 2 weeks.
Tapping to brake at low speeds is acceptable, but you can really feel the pedal sink down with less than adequate braking power while stepping on it to slow down at higher speeds (>80kmh).
Had the same experience after a brake flush on my C63 coupe. Initially I also thought there was a bubble or two in the system, but then I myself went through another two liters of brake fluid - that's more than enough for a full flush - bleeding all four calipers looking for the culprit (been doing it on my track cars for 15 years) and there wasn't a trace of air anywhere. Apparenty the fresh MB brake fluid they use has a somewhat lower specific gravity at first so it takes less pedal pressure for the calipers to exert the same clamping force on the rotors (the ABS kicking in on your car confirms that you are in fact braking with full force). The pedal feel gets slightly stiffer over time. Shop foreman - a die-hard racer, not just a track junkie - confirmed this. In other words, the brake system works perfectly - it's just the pedal feel that has changed, and it will get stiffer again once it absorbs some moisture. Give it another couple of weeks.
BTW, the MB brake fluid is excellent in all regards - it has a higher boiling point than ATE SuperBlue, Type 200 or the MOTUL stuff and is way less hygroscopic. I - and half of the PCA track junkies - am/are now running MB DOT4 brake fluid in our track cars.
BTW, the MB brake fluid is excellent in all regards - it has a higher boiling point than ATE SuperBlue, Type 200 or the MOTUL stuff and is way less hygroscopic. I - and half of the PCA track junkies - am/are now running MB DOT4 brake fluid in our track cars.
03-16-2015, 03:49 AM
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W204 C63 Coupe, W166 ML350 BlueTEC, 928GT, C5 Z06 & IS300 race cars, EQE 4Matic+ on order
Diablolis, thanks for the interesting insight.
It has been >3 months since the brake fluid was changed at the dealer so there has been more than enough time for the system to "absorb moisture" according to your explanation. And the situation only got worse the past 2 weeks.
Tapping to brake at low speeds is acceptable, but you can really feel the pedal sink down with less than adequate braking power while stepping on it to slow down at higher speeds (>80kmh).
It has been >3 months since the brake fluid was changed at the dealer so there has been more than enough time for the system to "absorb moisture" according to your explanation. And the situation only got worse the past 2 weeks.
Tapping to brake at low speeds is acceptable, but you can really feel the pedal sink down with less than adequate braking power while stepping on it to slow down at higher speeds (>80kmh).
In that case you may have an air bubble, you may have bolied the fluid (unlikely without VERY aggressive and repetitive braking, i.e. at a track), one of your brake lines could be damaged or you could be slowly losing fluid so when you press on the pedal some of it leaks out instead of maintaining constant pressure. I would get it checked out and posibly flushed again just to be on the safe side. Generally speaking, the dealers will do right by you and redo it at no charge if you had it done there before. There's obviously somethign wrong if the pedal went soft in three months without you boiling the fluid.
03-16-2015, 03:57 AM
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The car is at the dealer now as I type this so we shall see. Hope I don't get the dreaded "everything is normal" result.
Car is never tracked and I'm gentle on the brakes.
Car is never tracked and I'm gentle on the brakes.
In that case you may have an air bubble, you may have bolied the fluid (unlikely without VERY aggressive and repetitive braking, i.e. at a track), one of your brake lines could be damaged or you could be slowly losing fluid so when you press on the pedal some of it leaks out instead of maintaining constant pressure. I would get it checked out and posibly flushed again just to be on the safe side. Generally speaking, the dealers will do right by you and redo it at no charge if you had it done there before. There's obviously somethign wrong if the pedal went soft in three months without you boiling the fluid.
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03-17-2015, 07:59 AM
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Just got the car back and the brake pedal now feels like a million bucks - extremely firm at the top with minimal engagement to feel the pads squeezing onto the rotors, no heavy sink in on off braking like before
I don't know the exact details of what they did but the service advisor briefly told me over the phone that they did a full rebleed and checked the lines and brake servo.
Very happy with the result and hope it stays this way. Does that mean they did a botched job on the last brake fluid change? Because this day and night difference confirms that I'm not just kicking up a fuss.
I don't know the exact details of what they did but the service advisor briefly told me over the phone that they did a full rebleed and checked the lines and brake servo.
Very happy with the result and hope it stays this way. Does that mean they did a botched job on the last brake fluid change? Because this day and night difference confirms that I'm not just kicking up a fuss.
03-17-2015, 08:02 AM
#10
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Just got the car back and the brake pedal now feels like a million bucks - extremely firm at the top with minimal engagement to feel the pads squeezing onto the rotors, no heavy sink in on off braking like before
I don't know the exact details of what they did but the service advisor briefly told me over the phone that they did a full rebleed and checked the lines and brake servo.
Very happy with the result and hope it stays this way. Does that mean they did a botched job on the last brake fluid change? Because this day and night difference confirms that I'm not just kicking up a fuss.
I don't know the exact details of what they did but the service advisor briefly told me over the phone that they did a full rebleed and checked the lines and brake servo.
Very happy with the result and hope it stays this way. Does that mean they did a botched job on the last brake fluid change? Because this day and night difference confirms that I'm not just kicking up a fuss.
Yes, it sounds as if they left air in the brake system during the first service.
