Noise Diagnosis

[Richard01]

Hi All,

I'm running my pride and joy, a 2017 C43 Premium Black Edition. It's recently started to "thump" or "clunk" whilst changing down from 3rd to 2nd whilst breaking. Scenario would be approaching a give way or stop sign / roundabout. Only happens under breaking load! Originally the thump was only from 3-2 but I'm now experiencing odd noises in other gears. Mercedes advised another gearbox service is needed to be done either tho a gearbox service had been completed just a few months prior and again just before Christmas to try and diagnose the issue but this comes at a large cost and I'm not totally convinced its the fluids that are at fault. My thoughts are a mechanical issue but gears are smooth on the upshift and only noisy on the downshift.

Mercedes just want me to throw money after money whilst they guess at the issue changing parts with no real conclusion to the issue, money that I just do not have!

Can anyone help with ideas to try or know of any issues with this car. For reference it is the 9 speed.

Thanks in advance.
Rich

 

[Bobby Dazzler]

Hi All,

I'm running my pride and joy, a 2017 C43 Premium Black Edition. It's recently started to "thump" or "clunk" whilst changing down from 3rd to 2nd whilst breaking. Scenario would be approaching a give way or stop sign / roundabout. Only happens under breaking load! Originally the thump was only from 3-2 but I'm now experiencing odd noises in other gears. Mercedes advised another gearbox service is needed to be done either tho a gearbox service had been completed just a few months prior and again just before Christmas to try and diagnose the issue but this comes at a large cost and I'm not totally convinced its the fluids that are at fault. My thoughts are a mechanical issue but gears are smooth on the upshift and only noisy on the downshift.

Mercedes just want me to throw money after money whilst they guess at the issue changing parts with no real conclusion to the issue, money that I just do not have!

Can anyone help with ideas to try or know of any issues with this car. For reference it is the 9 speed.

Thanks in advance.
Rich

Rich, sorry to hear of your problems.

Three gearbox services ina few months doesn’t sound right to me - who did the last two gearbox services? If it wasn’t Mercedes then they may be saying it needs to be done again to make sure it’s done right and the levels are correct:

When did the kicking start relative to the previous gearbox services?

 

[MrGreedy]

Do you by any chance have any warranty remaining, or have purchased the car within the past 6 months? I only ask because it has been known (common practice?) for cars sales companies to use what are basically cheap stalling tactics so that when it eventually becomes apparent the issue is something major, they are very sorry but you are now out of warranty. What rotten luck on the customer.

Not saying that is the case here, but it has been known. Make your complaint in writing, with the details and send it recorded mail to the supplying dealer to ensure the facts and timelines is fully captured maybe?

 

[Richard01]

Rich, sorry to hear of your problems.

Three gearbox services ina few months doesn’t sound right to me - who did the last two gearbox services? If it wasn’t Mercedes then they may be saying it needs to be done again to make sure it’s done right and the levels are correct:

When did the kicking start relative to the previous gearbox services?

First Gearbox service was from a reputable garage (not Mercedes) but using all Mercedes parts and oils, second Gearbox service was done via Mercedes as they said they could not guarantee the work undertaken by the other garage. Clunking noise has been happening for approximately one year now but the issue is getting steadily worse and now not just 3rd to 2nd gear.

 

[Teego]

Before you go throwing a mountain of cash at MB, I'd see if these people can help. They were often reccommended by Honest John in his newspaper column.
FEDERATION OF AUTOMATIC TRANSMISSION ENGINEERS

 

[Bobby Dazzler]

First Gearbox service was from a reputable garage (not Mercedes) but using all Mercedes parts and oils, second Gearbox service was done via Mercedes as they said they could not guarantee the work undertaken by the other garage. Clunking noise has been happening for approximately one year now but the issue is getting steadily worse and now not just 3rd to 2nd gear.

To be clear though, the clunking happened before the first gearbox service? Would you have had the gearbox service done anyway or was it because of the clunking?

If the transmission has been serviced properly, at least twice in recent months, then I can’t see a third service making a difference, and makes me suspicious.

If the last place to service is was the same Mercedes dealer then it makes me think that they suspect they haven’t done something right and they want you to pay for it.

Maybe time to seek an automatic transmission specialist. Whereabouts are you?

 

[Bellow]

Hard shifts can be caused by factors external to the gearbox eg, I had hard up-shifts (4L 80E) when the MAF wasn't giving a reading (missing fuse) and the controlling ECU defaulted to WOT (maximum) line pressure.
Obviously different in that it's down-shifts that are your problem but if there is a particular strategy for say, the FBW throttle that controls engine braking during over-run/braking that has gone awry, then engine braking could be prevalent where it shouldn't be resulting in clumsy down-shifts.
Has the car been scanned (STAR) for any malfunctioning sensors/actuators?

 

[Larkone]

Would it not be worth checking the rear gearbox mount before going down more complicated investigations? Check the engine mounts while your at it.

 

[Bayleaf]

And propshaft drive shafts and wheels.

 

[Bellow]

General slop in the drivetrain should be apparent when the throttle is first closed - ie, without a down-shift. If this is occurring then the drivetrain components (including all mounts) are suspect but that isn't (yet) what the OP is reporting.

 

[Bayleaf]

I take your point, but as with anything it's always worth checking the basics first as it doesn't cost anything.

 

[Muckypaps]

Try manual shifting between the said gear change continuously for a stretch on a road, as the gearbox should self learn.
If you drive in auto it doesn’t get much chance, but if you do the changes manually repeatedly, it will give it a chance to adjust those changes with the problem faster,