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Discussion Starter · #1 ·
Hi,

I have a 2014 CLA 45 AMG with about 48k miles with sadly no performance modifications. I hear a thumbing/clunk noise just before coming to a complete stop. Sometimes it sounds like it is from the back and other times it sounds like it is coming from the back and the front. Sounds and feel like a transmission issue.

I took the car to the local Mercedes and they report that it is "working as expected." The GLE 250 4matic they loaned me does not have the issue and I think the drivetrain is very similar if not exact. I explained this to the tech, but he just basically dismissed my comparison.

I lifted the car and unplugged the power to the rear differential solenoid and took the car for a test drive. The noise is completely gone.
The fluid in the rear dif. was changed about 2k miles ago but the problem was present before the fluid change and persists after the fluid change.

Any ideas? Suggest removing and inspecting/replacing the solenoid?


Thanks!
Aaron
 

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2021 AMG CLA 45 S Digital White w/Performance Package
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I was told by the Merc tech at my local dealership that the distinct 'thud' that is heard when slowing was a peculiarity of the 4-Matic system and was quite 'normal'. I had it in my 2016 CLA, and I still have it (although not as noticeable) in my 2021 AMG 45 S.
 

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Previous cases resulted in replaced diffs
If its just clumsy engagement well maybe let it go
But if mechanical klanking shows up it may be too late by the time you hear it
 

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Discussion Starter · #4 ·
I was told by the Merc tech at my local dealership that the distinct 'thud' that is heard when slowing was a peculiarity of the 4-Matic system and was quite 'normal'. I had it in my 2016 CLA, and I still have it (although not as noticeable) in my 2021 AMG 45 S.
Nice ride DrOzCLA, congrats. I came from a C350 (non 4matic) and did not experience any peculiarities so I am a little surprised by this. It does not explain why the GLA they loaned me does not have this.
 

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Discussion Starter · #5 ·
Previous cases resulted in replaced diffs
If its just clumsy engagement well maybe let it go
But if mechanical klanking shows up it may be too late by the time you hear it
Previous cases resulted in replaced diffs
If its just clumsy engagement well maybe let it go
But if mechanical klanking shows up it may be too late by the time you hear it
It is somewhere between clumsy engagement and klanking. Each time I come to a stop it is a little different. 48k is pretty low miles to be experiencing something like this. I am going to check if rebuilding this is an option. Thanks DrOzCLA and JMC.
 

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Could be software updates needed or could be the differential clutch slippage. The latter could be due to the incorrect fluid level or type of fluid used (which in your case , probably ruled out), or you may have to change out your rear differential.
My old 2000 Acura TL had the infamous Thunking sound when accelerating from stop and decelerating to a stop. Honda had then issued a recall on all vehicles with the affected transmission, and provided replacements with upgraded clutch pack and software. By that time, I was so fed up of it, I simply traded it for my 2002 BMW 330i M-sport (a beauty of a car).
 

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Hi,

I have a 2014 CLA 45 AMG with about 48k miles with sadly no performance modifications. I hear a thumbing/clunk noise just before coming to a complete stop. Sometimes it sounds like it is from the back and other times it sounds like it is coming from the back and the front. Sounds and feel like a transmission issue.

I took the car to the local Mercedes and they report that it is "working as expected." The GLE 250 4matic they loaned me does not have the issue and I think the drivetrain is very similar if not exact. I explained this to the tech, but he just basically dismissed my comparison.

I lifted the car and unplugged the power to the rear differential solenoid and took the car for a test drive. The noise is completely gone.
The fluid in the rear dif. was changed about 2k miles ago but the problem was present before the fluid change and persists after the fluid change.

Any ideas? Suggest removing and inspecting/replacing the solenoid?


Thanks!
Aaron
Thump is normal given the transmission. I thought someone hit me at a stop light when I first bought the car. I have rhe GLA45 but same trans. Weird I know but still does it and I only have 30k on it - it’s a 2015! And I drive it hard
 

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Discussion Starter · #9 ·
Thanks for the feedback everyone. Just to try, I removed the electrical connector to the rear differential and the noise went away. Confuses me why it would engage rear wheels just before coming to a stop though. oh well.
 

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Experiencing the same thing on my 2022 CLA45, it is so noticeable that the whole car would vibrate in addition to the "thud" when coming to a full stop. It seems to happen at the exact moment the gear drops from 2nd to 1st.

I took it in for the dealer to inspect and they did a transmission reprogramming. The issue was still there the day I picked up the car about a week ago, but it was a lot better yesterday when I went out for a drive. The "thud" wasn't as loud and the vibration wasn't as noticeable.
 
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