alyshehata

Hi guys,

I am wondering if this is normal on a W205 where I am experiencing a slight shake in the steering wheel and brake pedal when braking lightly on comfort or eco mode. The shudder only happens for about a second after the downshift from 4th gear to 3rd gear. It is interesting that I do not notice any vibration when applying the same braking on Sport+ mode. I'm wondering if this is normal and if anyone else noticed the same thing. All other downshifts are pretty smooth (although a bit of a jerk forward but no vibrations).

ManiacGT

Something like this would usually be warped rotors (discs).

alyshehata

That's what I originally though about, but it only happens in the instant the downshift occurs from 4th to 3rd gear. It doesn't happen anytime else, and it doesn't happen on S+ when applying the same amount of braking. My guess is it's tranny related.

Hapa88

I'm a little confused by your description, so help me understand. You refer to both braking and downshifting (4th to 3rd) which implies "engine braking". Do the problems you experience happen when you are braking (as in using the brake pedal)? Or do you feel the problems when you're engine braking (as in lifting off the accelerator and letting the car coast and reduce speed by using the engine torque)?

Based on what you describe, the only thing I can think of would apply to the ECO mode and its disengagement and reengagement of the transmission from the drivetrain during coasting.

Hapa88

Note that "warped" rotors are a myth. 99.9% of the time it is uneven brake pad deposits left of on the rotors that cause vibration. See this white paper by Stoptech for more info:

http://www.stoptech.com/technical-su...nd-other-myths

alyshehata

Thanks for your reply. I'll go ahead and clarify exactly what I mean. Basically as I approach a traffic light for example, I'll start to lightly hit the brake. I feel a little jolt every time the car downshifts but that is normal engine braking since it is switching to a lower gear. However, from 4th to 3rd gear, in addition to the engine braking feeling, I feel a vibration in the brake pedal as well as the steering wheel for about a second. It kind of feels as if it takes the car that long to finally get into the 3rd gear. So in summary, the vibration only occurs when the transmission shifts from 4th to 3rd if I'm braking lightly to come to a stop. It does not happen in S+ and I do not feel the vibration if I brake a little bit harder than I would like.

alyshehata

Just reset transmission adaptation and drove around for a bit.. It seems to be still happening. I do not recall the loaners I had exhibited this issue so I feel like it might be something wrong with the transmission. It is really minor, but definitely bugs me when going through stop and go traffic.

Shadwell

It's likely uneven deposition on the rotors..

Obtain some ferrous iron cleaner (eg carpro iron-X)
spray a mist of the product onto the wheels face, barrels, calliper and discs... Move the car forward to cover the whole disc..

allow it it to dwell for a minute or two, things will turn purple.. That's normal...

use ser a wheel cleaning brush to get everything agitated.. Then rinse first with a lot of water ( the purple solution will rinse away. ) then wash with car shampoo as normal...

If if you have a leaf blower dry the wheels, discs and rotors..

Take for for a drive and check again....

alyshehata

Thanks for your reply. However, do you think this will help mitigate the issue given that it is only caused in the instant the car downshifts from 4th to 3rd gear?

Shadwell

It's a process of elimination...

the he transmission has no connection to the front wheels (not 4wd right? Pls confirm )
So IF it's brake elated that's an easy elimination at little to no cost which I have experienced as a notable contributor to the brake judder through the steering sensation...

If if after doing this it's no different then of course that then points to the drivetrain which I imagine you are unable to action at home...

Without being in in front of the car and observing the issue the process of elimination is the next best approach....

Hapa88

My thought is it could be the transmission ECU programming. I thought I remember reading somewhere that people have had their transmission programming updated at the dealership. Have you had it done at all?
Read this thread. People mention the TCU (Transmission Control Unit) update.
https://mbworld.org/forums/c-class-w...ift-issue.html

Paul Davidson

I have exactly the same problem
I have had the discs cleaned and new sets on front and rear and it is still happening .So annoying for a top end car
Forums in the states suggest that the design of the discs are faulty and overheat therefore expanding whilst driving causing the juddering .
others suggest that the is a software issue that causes the system to brake lightly thinking that the discs are wet from rain . Therefore over heating them .
I have spent out a lot of money trying to solve the issue but I am now taking car in under warranty to try and solve the problem

CJG

I tend to agree. Sounds like tranny ECU needs to be updated or simply reinstalled. I had a similar problem in my W204 and this solved it.

alexasa

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