Cli63

So, my car was perfectly fine this morning, took it to the shop do an oil change this afternoon. I was present the whole time, and nothing else was touched apart from draining and filling the oil. On my way back home, noticed I have very little brake peddle feel. Also after i parked the car, the pedal would become very hard. The pedal would go completely mushy again when i start the car back up. The most recent brake work i had done was about 2-3 weeks ago. Changed brake pads, stainless lines and fluid. Did not have any trouble until today. Also checked the master cylinder and it was very full, definitely above the "max" line.

Anyone know the cause of this?? Will be taking the car straight back to the shop first thing tomorrow, but would like to narrow down the cause. Much appreciated for any ideas and clues.

tpliquid

maybe air in line. usually pedal gets hard when engine off thou.

Cli63

I know the pedal should get hard, but currently the pedal has no travel distance. Have to push fairly hard to just start the car. Just to double check, i went into my friend's bimmer and his brake peddle at least has some space to move.

Also my question is, if there is air in the line, does it usually take that long to get noticeable?

Diabolis

Pedal hard / mushy when car is off / on respectively is 100% normal. And, I suspect you checked the brake fluid reservoir level, not the master cylinder.

I am not sure what you mean by having no brake pedal feel... the "feel" is the amount of force you have to press with (i.e. the force it exerts back on your foot) to produce a certain level of braking. Are you saying that you have to stand on the pedal really hard but the car barely slows down? Or the other way around (you barely touch the brake and the car comes to screeching halt and your ABS kicks in)? Are you referring to the amount of pedal travel you have? An air bubble in the brake lines makes the brake pedal sink a lot further down than normal while the car is not braking as hard as it should. Is that what you're experiencing?

Cli63

Sorry, when i said master cylinder meant to say reservoir, got my term mixed up there. As for the engine stopping stuff, i guess it was just placebo on my end. Just never really noticed the pedal to be that hard.

And when i meant no feel, i mean the brake pedal had a lot of travel distance before i would get any feedback from the brakes. Had push the pedal about half way just to brake from 60, when usually it only takes quarter.

Anyhow, car fixed itself when i started her up this morning, just got back from the shop to double check everything. No signs of any problem. Do appreciate, the advice you've given.

Diabolis

Increased pedal travel to achieve the same braking force is not normal and could be very dangerous. I'd have it looked at if you ever feel that you have to press harder and/or that the pedal travels further down than it should for you to slow down from any given speed. If there's one thing I wouldn't take any chances with, it's the brakes.

The slowly sinking brake pedal when you step hard on the brake pedal with the car running but stationary in P is normal on the C63 - but it should NOT sink to the floor (i.e. it should eventually completely stop moving at a certian point before the pedal sinks to the floor).

Drive carefully for the next few weeks and see if you feel any changes. If you notice anything unusual, have it checked by the shop that did your brakes. Did you use the the OEM MB brake fluid? While it is very good performance-wise, the MB brake fluid has a lower viscosity than other DOT4 brake fluids, and the viscosity slowly increases as it ages and absorbs moisture, so new MB fluid will always result in a somewhat softer pedal feel, but NOT MORE PEDAL TRAVEL to acheive the same stopping power.

Cli63

No i didn't use the OEM brake fluid. I bought a brake package from Tal @ ACG, so i think it was motul 600 that came with the lines and pads. But yeah will definitely keep an eye on the brakes. Stopping a car is always the most important thing, don't want to take any chances here.

Diabolis

Motul RBF600 is very good stuff, but it is more viscous than the OEM MB fluid... so you'll have to press somewhat harder on the pedal than with OEM fluid to achieve the same stopping force.

hyunman

...halp

Short Version:
Not sure if it's just in my head or not, but my brake pedal travel seems slightly longer than before. Bothered me to the point of uploading this video.


Does this travel distance seem normal? I'm only pressing relatively lightly in the video, not slamming my foot at all, and the engine is on. Might be hard to make out from the video, but the brakes feel like they don't start engaging (I feel less resistance) until I get further down (about where my foot slows down in the video). Everything feels normal ONCE I reach this point - as far as braking ability and also feedback in my foot. But it just feels like the pedal needs to travel further down to reach that point. Am I just imagining this or does this travel distance seem longer than on all of your W204 C63's?

Long Version:
I did a brake fluid flush this weekend using the Motive bleeder and Castrol SRF, maintaining about 13 psi and sufficient fluid in the Motive tank and reservoir at all times. I didn't touch the brake pads at all. Everything seemingly went well, made sure I bled enough until I saw no more air. After bleeding all 6 ports (2 per front caliper and 1 per rear caliper), I released pressure from the Motive pump and then took the adaptor cap off the reservoir. The reservoir was full, so I took out the excess fluid from the reservoir using a syringe. I set the level to halfway between the Max and Min markers.

When I test drove, I immediately felt like the brake pedal had to be pressed deeper than I remember. I drove around town to see if it would feel better, but no. The braking of the car itself didn't feel affected at all, just took more pedal travel to get there.

Did some massive reading up that night, and concluded that I got air in the system and/or that it was because I didn't fully flush the ABS system using the STAR system like the dealer does (didn't know about the STAR/ABS deal before my DIY attempt). Out of panic, I scheduled my car to get a brake flush from a local MB dealer today. After picking the car up, the pedal felt the same as it did when I brought it in. I checked the reservoir and the level was now at the Max marker, which made me think that they probably did the flush. The nearest SA asked what was wrong and I explained. He then got in and tried it out himself. Came out saying "it feels absolutely normal to me."

Obviously, the SA has an incentive to say what he did, but I'm also starting to doubt myself. Sucks how this is so hard to quantify. But before I go back to get it reflushed again, could someone advise? Appreciate any input..

hyunman

Gentle bump...
Anyone?
Thanks in advance

zcct04

One of the risks of too much late-nite internetting is that the pieces can get jumbled. If I recall correctly, the STAR/ABS deal is a W211 problem and not an issue on our cars.

This too may be an artifact of too much late night web exposure, but I also recall reading that the Mercedes brake fluid becomes more viscous over time. A good system flush would replace everything with less viscous fluid and would in fact be quite likely to change the feel of the brake pedal.

My vote is with your SA - this sounds absolutely normal to me.

hyunman

Oh jeezzz...you're right. I just re-googled "DIY brake fluid flush C63" and clicked on the the first link from mbworld, where I saw the STAR/ABS deal mentioned, and it's not for the W204 like you said. It looks like I jumped the gun and assumed the very first result from mbworld would be for the C63. Thanks for your input about the fluid viscosity too zcct04...I feel much more at ease now...

Diabolis

Already answered - see (my) post #6 above. The pedal will almost always feel softer - which can be easily misinterpreted as being 'mushy' - with fresh brake fuild, but the actual pedal travel and braking performance should be the same. If you have to press the pedal HARDER or FURTHER DOWN than you used to in order to achieve the same braking performance, you could have an air bubble trapped in the system. If you simply don't have to press as hard with fresh fluid but the car still stops as it should, that's perfectly normal. If you had MB do the fluid flush, chances are it is 100% fine - and that they also flushed out your $80/liter SRF and put in fresh MB fluid (which has a lower viscosity than the SRF).

hyunman

Thanks Diabolis - yea I just wasn't sure if I was feeling a 'softer' feeling or a 'further down' feeling, or even both. Hard to know exactly without having a solid frame of reference of what it was like before all this. I never cared to pay special attention to the brake pedal feel and travel distance before this past weekend

I think I overlooked this viscosity factor and it makes sense now. After all, what I've been perceiving as 'more travel' is almost insignificant in terms of the actual distance when I review my video.

Anyway, between the SA and familiar forum names like you and zcct04, I'm am now at peace. Thanks guys

Sosyal08

Pardon me...
what us the "STAR/AND deal"? I just did a fluid change on my w211 2008 e350. I understand I don't have SBC, and have ABS brakes. I have a hard pedal with engine off now, and a longer than notmal travel before engagement of brake stopping-feel. I'm shot sure if it's just new fluid needing time to become more dense or more air in the line somewhere (I bled system twice now with Motive Pressure bleeder). Any guidance would be appreciated...
thanks