Hello.
I'm the owner of the beautiful C300 RWD Estate with airmatic suspension (I took the car at 11.2015 from dealer).

The car is amazing, but I have some problems with it.

After I think 1-2 months (I'm not sure if the problem exist since beggining) I observe strange problems with traction.

I will try to describe it. Let say I'm driving an ideal flat road about 100km/h and take off the leg from the accelerator pedal, set up the steering weel that car is driving straight. After few seconds next when I will put the accelerator (for example medium dynamic set) the car starts moving to the left. When I stop accelerating, the car stops moving to the left. When I accelerate again, the car moves to the left again. (it looks like the car changes its position on the road, like the rear axis moves to the right and set up front of the car to the left).

I went to the dealer which sold me the car, they have checked everything, geo is ideal, nothing to catch. So I decided not to escalate the problem and drive the car. But after few weeks I can still feel that the car is annoying moving to the left during accelerating. I went back to the dealer, and they said that it is strange and they will call for the technican. I'm waiting since 2 months and no answer - I decided to go to another dealer. They took the car and said that really I can precade other cars during accelerating. The second service check everything again and again nothing you can catch that is bad. So we have changed from winter tires into summer tires - the same effect (but the wheel service told me that the rear right wheel has a litle more used tread - is it normal?).

Next they check suspension again, and the master of the service said that some rubber next to right rear wheel need to be changed - strange, because the car has 8k kilometers done ?!?;-(.

I'm going to the service to change that broken rubber next week, but I think that it is not the real casue with moving car during accelerating.

Is it possible that the car can change the traction during acceleration?
Can the weight of the engine changes the traction of the car because of careen to the left during acceleration?

 

The rubber is likely the cause. When accelerating or decelerating a malformed or broken suspension bushing (rubber) can mean the geometry changes. I have first hand experience of this on an old car.

I'm quite envious you have a C300 estate, here in the UK they only sell the C200.

 

Hello.
The C300 is accessible in Poland since the second half of the 2015.

I will come back here after changing the rubbers(next week), I really wonder if it was a cause of my problems ;-(.

 

Hello.
I got back my star after two days in service. They have changed broken rubbers and the car drive properly ;-).

BUT...I still can feel a little strange experience. Before the change of course car was unstable on the road and had traction problems (I felt that the rear of the car was trying to leave the road ;-) - now it is ok).

Now I still can feel a little that when acelerating the car has a trend to move to the center od the road (to the left). I can feel it when accelerating medium or really hard.

So I have took three NEW Mercedes Benz cars from the saloon:

- C180 RWD
- C250 RWD
- C300 Coupe RWD

* the experience can be felt more with the growing the power of the engine

ALL this cars have the same behavior. Is that because of the RWD or some kind of physics rules?

I talked with the master of the service and they agree with mee that they can feel the same, but said to me that I'm 1/100 clients which can feel it.

What is your feeling?
Regards.

 

If geometry is correct this could be tyre pressures or road camber.

 

Hello.
All these tests I made having few days or hours for each car.
I did tests on the flat high way roads, also on simple but flat roads.

ALL the cars have the same effect...

I think that it is the effect of the RWD system with bended road to the right.
In consequence the rear axle slips a little on the bended road during hard acceleration and set up the front of the car to the left.

Best regards.

 

Ah there's a bend? In that case yes without an LSD under full power you will experience some torque steer on a bend.

 

Hello.
Not exactly. With medium accelerating I can feel the same behavior (of course with ESP system).

You can reproduce that in a simple way:
- go to the high way
- set up about 130 km/h using tempomat
- set up the steering wheel that the car drives generally straight
- get out your hands from the steering wheel
- next release the tempomat using tempomat BUTTON(do not touch the steering wheel!)
- wait 2-3 seconds to allow the engine to move back to its normal position
- next then the car will start moving do the right, all cars which I tested (four NEW MB cars) do the same

That is the proof that when having a torgue on the rear the car has a trend to go left. When you removed the torgue, the car will 'go back' to the right.

Regards.

 

Thinking....
With subframes mounted on rubber bushes (to isolate cabin from driveline and road NVH) it is foreseeable that under torque there will be an alignment change (albeit minor).
After all if some movement is allowed for NVH then of course same movement coud alter geometry..


Agree, ideal would be isolation of NVH planes of movement from driveline load forces..


To reduce driveline movement in this design would neccesitate a more robust isolation media, and likely increase NVH.. removal woudl eliminate movement but create worst scenario for NVH... as an example the new BMW M2 had direct mounted rear subframe.. it causes appreciably more transmission of NVH to the cabin, but creates for very high drive feedback transmission..

 

Hello.
Thank you for extended reply. Now I understand the reasons.

But in my opinion, each notsunday driver can feel that behavior and it is not ok to a premium class car.

Best regards.