Brake Shake??

[davidz68]

Well, it's winter here in Wisconsin and I'm driving this car in snow for the first time and am encountering something I haven't in any other car I've had.

When applying the brakes on wet/snowy road it seems the anti-lock kicks in and the brake pedal shudders really bad. I do stop but it just doesn't feel like it should do that.

I had anti-locks on my last car and it didn't do anything like this.

Any info would be appreciated. Happy Holidays!

99 C230 Kompressor. Stock cept awesome tint from Tinter101.

[adamsry]

Is the warning triangle coming up on the cluster when your breaking? Also do you have the trannie in the S or W mode?

[davidz68]

Hi. Thanks in advance.

Yeah, the light flashes when braking. I've tried both WS modes. I usually only use W if it's really wet and I can't get any traction. If my wheels spin that warning light will come on, but that's normal from what I've read. I'm not really alarmed by the fact I feel something because it is stopping quickly, it's just the fact of the severity of what I'm feeling vs. what I've felt on other cars.

[anf6789]

does that in mine too, kind like some ones shaking the brake pedal back and forth?

[Logic]

the anti lock brakes in my 2001 dodge intrepid does that same thing. scared me at the time since i wasn't used to anti lock but you hear this sound come in and out and from what i been told that is normal. as far as it in my c230k i don't drive it in the winter months so i m not sure but the way you explained it it sounds normal.

[JRE320]

How about your brake pads and rotors?
Did you replaced them? If not then it's time for you to replace the brake pads and have your rotors resurface.

[davidz68]

There's only 50,000 on the car so I doubt it's that. I am taking it in here for a service check and plan on mentioning the brake thing at that time so I'm sure they'll get looked at.

[JRE320]

Originally posted by davidz68
There's only 50,000 on the car so I doubt it's that. I am taking it in here for a service check and plan on mentioning the brake thing at that time so I'm sure they'll get looked at.

Even if the pads are still o'k but your rotors are warping. You still have to change the pads and resurface your rotors. ;)

[SLAMMED_C]

it sounds like a pulsation in the brake pedal from warped (out of round) rotors.
if they cant be machined (depending on severity of out of roundness) they will need to be replaced. id recommend replacing them. i have never had a set of warped rotors i could machine straight again.

[DynoXG]

Yeah, I'll agree too on warped rotors. Had that happen on one of my previous cars and it went away after replacing the rotors. They tried to resurface them first but the problem was still there a bit.

[adamsry]

It sounds to me like the BAS is kicking in prematurely. This is a brake assist program that is an active safty feature if the sensory i beleave it measures yaw ?? is bad then the car will think that your constantly in brake for emergency and then cause the ABS to pulsate. There are 4 sensors in the weel hubs and the yaw sensor. This is the MB Discription.

The Brake Assist System (BAS), an electronic system by Mercedes-Benz, interprets the braking behavior of the driver and initiates the full braking effect when it identifies an emergency situation. This reduces the braking distance substantially.


Here is the engineering foundation for BAS:



Conventional braking systems usually use engine vacuum to increase braking capability. Instead of relying solely on vacuum power to provide effective brakes, an electric pump pressurizes brake fluid to provide power assist for BAS and the necessary brake force for 4ETS.

The pressurized brake fluid is stored at about. 180 bar (2600 psi!) in a reservoir known as the accumulator. From the accumulator the high pressure brake fluid is supplied to the hydraulic operating cylinder in the master cylinder assembly. Commands to utilize the pressurized fluid comes from either 4ETS or BAS. When the brakes are applied and BAS deems it necessary, a lever connected to the brake pedal releases varying amounts of the high pressure fluid to assist in stopping the car.



Most drivers, under normal braking conditions as well as under emergency conditions, start out with little brake pressure and whenever necessary they will increase their pedal effort. In an emergency this behavior leads many times to a crash since the car could not be stopped in time. Those situations require maximum pedal pressure from the beginning - if necessary the effort can be reduced later in the process.



With other words most drivers do not use the ability of the brakes to their advantage - BAS automatically corrects that. The system recognizes emergency situations within milli seconds and releases pressurized brake fluid into the system as soon as the driver touches the brake pedal. As soon as the driver releases the brake pedal, BAS kicks back into a standby mode.



BAS creates a much higher stopping force for emergencies than most drivers are ever able to generate. By doing so BAS helps to prevent accidents
_



Just another good reason to drive a car made by Mercedes-Benz

[jnolte]

bas stops ur car so fast its gotten me rear ended

[Fizzle]

It is completely normal. I live in Chicago, so I am pretty used to the ABS kicking in. I just got new pads and rotors 1 week ago. On slippery roads and street my pedal would shudder when the ABS activated. It shuddered before and after the new rotors and pads. i know it feels really weird as it shakes your foot but its ok. Even my dads '02 S430 does it. if you don't like the feeling the best thing to do is slowdown in slippery conditions, and make sure your not still using your summer tires.

[lamf]

no worries it happens on all cars in the snow sometimes. i guess nobody is from new england here

[davidz68]

Thanks to all posting replies.

I think it is the BAS that was mentioned. I took the car in for a look at the brakes/rotors and were fine.

I was kind of hesitant on the rotor theory because under "normal" braking I didn't feel any such pulsations. But seeing a number thought it may be that, I thought it best to get it looked at.

Thanks for the great information. I really appreciate it.

Happy Holidays to everyone!

[C280_Spawrt]

im not sure if it is the BAS, this is my 3rd winter in NY and anytime i aplly moderate braking on slippery conditions the pedal shakes like that. Normal abs if u ask me