hibino

I just traded in my half year old GL350 with a same equipped GL350 but with the active curve system due to the old GL is rolling too much. I have to say the active curve is amazing but I found that I can hear/feel the car is making some sort of machine parts moving sound(like the sound of a robot moving its arm up and down in a movie) when turning left/right in a sharp angle(like 90 degree in a traffic cross) at about 20-30km/h, but I can't hear/feel the sound on high speeds or small curved roads.


My old GL doesn't make any kind of sound when cornering and it only happens in sharp corners so I guess the sound is coming from the active curve system.


I am not too sure if this is normal since I googled around and can't find anything about that active curve system will make noises when acting, so I am wondering if anyone do hear/feel the sound like me? Thanks.

jacobsung

That sounds like your airmatic suspensions.

My 2013 GL350 with Active Curve System makes no noise during turns. However while driving once in a while, it makes a hissing noise by airmatic suspensions. Especially, when I park and get out, it makes this big hissing noise like when a school bus (or a dump truck) stops, and also air pump noise even ignition is off.

When I drove 2015 GL450 (without ACS), I did hear more like your "robotic" servo noise instead.

hibino

Yes I get the hissing noise when parked after a drive for both GLs since they are all air suspensions. Both GLs are equipped with air suspension and same wheels/tyres so the only difference they got is the active curve system.


From your two GLs I guess the robotic sound when turning is not from the active curve but more like a different build quality thing?

hibino

It is late night here and I just drove my car out and did some tests. I found a wide road with no cars around and made the car keep going in a circle(360 degrees).


There was no noise when the car is circling in a constant speed. But when I hit the accelerate pedal there is another sound other than the engine like I described above that is constantly on when the car starts accelerating, but will disappear after I release the accelerate pedal.


The sound is clearer when I circling clockwise but smaller when I circling anti-clockwise, I guess it is because I am driving at the RHS and the mechanism is doing more on the right wheel when going clockwise.


So, I am still not sure what the sound is but I feel it is the active curve trying to balance the car when speed changes, but still, I don't know whether the active curve should make any sound or not...

Count Laszlo

Are you sure that's not the turbos spooling?

jacobsung

http://techcenter.mercedes-benz.com/...em/detail.html

hibino

No, it sounds different than the turbo and only happens in a sharp turn.


Yes I've checked this page before I go for the active curve but there is no information regarding whether the active curve will make some machine moving sound on the internet...

Teemu

Had to register just for this topic; YES, I have the same strange sound coming and going but mostly noticable when turning to right. I have tried lowering and rising the car and it does not make any difference.

I also have it with low speed, could it be somehow related to pressing brakes just before turning the wheels?

43221B

It's been a while since I've read the tech specs on Active Curve, but what it sounds like you are hearing is a solenoid valve closing when you start to make your turn. Basically, hydraulic fluid can pass through the valve when you are driving in a straight line allowing the wheels to travel up and down independently. When you start to corner, the valve closes and locks the sway bars making it so that the wheels on both sides of the car must travel up or down in unison.

If it is annoying you, I would ask the dealership to address it.

Teemu

Thanks for your reply, 43221B, that is something to start working with. I took the dealer for a ride few weeks ago, naturally car was silent as a mouse in every corner, as we all know when trying to present the problem to dealers.

I have only limited warranty with the car ( 2013 model and I live in Europe) if this is something else than a "feature".

Great forum!!

hibino

Thanks, Since there is not much info about the active curve system on internet so I googled a lot on the active anti-roll bars few days ago and come up a page explaining the BMW's Active Roll Stabilization which is a nearly same solution as the Active Curve System. So since there are machine controlled parts for this feature there will be sound coming from it.


I took one of the mechanic from my car dealer for a short drive today see if he can hear the sound. He said he can and said the sound is normal since the car is adjusting it's level to keep car body flat, and the sound is from the active curve system.


I guess I just have a very sensitive ear that hears a lot more than normal people, because there is no one talking about the sound from active curve system before. Also, There is a very tiny squeak sound when I turning my steering wheel to the right, I can hear it very clearly no matter on driver's seat or passenger's seat, but when I went to the dealer, the car sales, their service manager, and the mechanic himself sitting on the driver's seat and keep turning the steering wheel but none of them can hear it, at last the mechanic has to take the whole steering wheel out in their workshop in order to hear the noise.


Anyway, so the active curve system does make a sound when adjusting the body level, it is just whether you can hear it or not...

Elric99

My 2014 w/ active curve does make a slight sort of "humming" noise, sometimes when turning right. And typically only audible at lower speeds like you described. On mine it sounds from the driver seat as if it comes from the rear of car. I've asked the shop to look into it a couple of times, they can't seem to replicate it or fix it.

jacobsung

Active Curve System is such a wonder option. You won't know what you are missing until you have one.

hibino

Count Laszlo posted a TSB in his post https://mbworld.org/forums/gl-class-...unk-video.html


The LI33.20-P-054920 says:

I think this might be the problem I have on my GL since it specified "turning corners". But my dealer can not hear it so I guess I have to wait when it becomes more obvious.


Well, it turns out the sound might not from Active Curve System at all...