Mercedes ML350 front end noise

mercedes-benz
m-class

#1

OK, so this is a 2012 ML350 Blue-tech with around 31,000 miles on it. Lately when it is warm (either by driving for 30 minutes or more, or by outside temperature of 80 plus), it has been making the strangest front end groaning noise when coming to a stop and when pulling away. It sounds like the front end suspension is “groaning”. It does’t have to be a hard stop, gentle will do just fine. The car comes to a halt, the front end dips slightly - “groooaaan” (perhaps more on the rebound than the initial dip). You start up again, the front end unloads, and “groooaaan”.

Very disconcerting on a car as smart as this. Tom and Ray know this car - this is the one with the “smart radio” (switches channels at voice command…)

The dealer is stumped. They have the car for the third time now and even though both a mechanic and the shop foreman have been shown the problem (taken for a test drive ), they have been unable to come up with either a diagnosis or a fix. They replaced the front sway bar links once to no avail.

Any thoughts?


#2

sway bar links tend to make a clunk or a rumble, NOT groan


#3

The vehicle is a bit young for this but have they not considered the sway bar bushings that mount it to the frame or subframe as the case may be?

No idea why they would think an end link would groan.


#4

I think it is the entire sway bar linkage (including the bushings of course) they replaced, but that didn’t get rid of the groans…

I suggested that perhaps it is a premature strut failure, but they insisted that that would result in more “knocking” type noises and the front end would be noticeably bouncier…


#5

I was thinking struts too. When the wheels stop, the rest of the car wants to keep going forward, so that inertial force tips the front of the car downward . Sort of like if you trip, you fall down and forward. Stopping definitely compress the front struts. Same on accel, only in that case the rear of the car goes down, and the font goes up (just like Herbie in Disney’s The Love Bug movie).

Has anybody stood on the fender and jumped up and down? You might not want to be there when it happens. But it could provide a clue anyway. May just be a sample defect with the struts or some other suspension component.


#6

I’m afraid that I can’t be of much help on this problem. The sway bar bushings are usually the prime suspect and seeing as how that’s been done that angle has been eliminated.

Things such as a dry suspension or steering component (ball joint, tie rod end, or even the strut itself could be responsible for this but I have no way of knowing.

I do note there are several service bulletins for noise but one is related to a hiss sound which may require replacement of one or both struts.
The other references a groan noise caused by an axle.

One would hope those bulletins have been taken into consideration when they were looking the car over.