W213 E220 - Creeping forward when in P

[alt]

Hi all,
I have a 2017 W213 E220 Premium Plus, still under warranty.

I went to the dealer with this issue and they say they can't replicate it, so thought i'd ask here incase anyone can shed light, or whether it's normal (I doubt it).

This is an intermittent issue that happens, usually when the car has been brought for a short run but is still cold. Let me give you an example...

I drive off in the morning and complete a 3 mile run. So the engine is still cold.

I put the car into P (note that the parking brake is not activated) on a level ground and leave the engine running.

SOMETIMES, after a few minutes, the car will give approx. 5 'nudges' forward. The total distance it nudges forward may only be half an inch, but if you're in the car you can feel it.

The only way I can describe this, is imagine you're at traffic lights when your foot on the brake, but still in D. You ever so slightly let off the brake and you can feel the car trying to move forward. Well imagine 5 bursts of this. It's not violent or anything, more just like the car is trying to still go forward and something stops it, and this happens approx. 5 times.

After this, all is good.

This is a weird one... it's as if the brakes have been applied when I put it into P, but it's still in gear, and the car is trying to go forward before being stopped.

Over to the floor....

 

[whitenemesis]

Even without the parking brake applied when in P the transmission parking pawl will be engaged, the transmission is locked.
It's possible for the car to rock back and forth due to the small amount of play between the pawl and teeth.

 

[CaptainChaos]

But, but, but.... on a new Merc like the one mentioned when you press P on the gear stalk that applies the parking brake. Or you can even just turn the engine off and open the door. That does the same thing and you will hear the parking brake motors wind on.

It isn't P on the transmission selector and then apply the parking brake separately like on older cars.

 

[CaptainChaos]

Just a thought - the handbook for mine advises that the parking brake can make adjustments after being applied. I wonder if this is what you are hearing?

Cars with conventional cable operated parking brakes and rear disks used to suffer from rolling away if they weren't left in gear. What happens is the rear disks are hot from use, the parking brake is applied and the owner leaves the car. As the brakes cool (and contract) the parking brake is no longer as tightly applied as it once was and the car can roll. An electronic parking brake can wind itself on further to allow for this.

 

[whitenemesis]

Cars with conventional cable operated parking brakes and rear disks

Don't these cars usually have a small drum parking brake within the disk mounting bell? My S203 and the W219 did and my RC does. So as the brakes cool the drum shrinks onto the parking brake shoes. But then rear brake rarely get warm enough for it to be an issue

 

[Germgh0st]

I think my W205 does indeed have separate parking brakes and foot brakes, because if I put my foot on the brake, engage the parking brake and then take my foot of the brake the car nudges forward a little as it comes off of the main brakes and settles on the parking brake.

 

[markmifsud]

Looking at EPC, the 213 is only fitted with a caliper brake.

 

[CaptainChaos]

Don't these cars usually have a small drum parking brake within the disk mounting bell? My S203 and the W219 did and my RC does. So as the brakes cool the drum shrinks onto the parking brake shoes. But then rear brake rarely get warm enough for it to be an issue

That's often known as a "top hat" disk and it is a better solution, but is more expensive and complicated, so it isn't always used.

 

[E55BOF]

That's often known as a "top hat" disk and it is a better solution, but is more expensive and complicated, so it isn't always used.

Sign of the times, I suppose; in the mass market, which is where MB now largely is, cheaper but adequate will do.