Hello everyone,

I have a 2009 S450 4MATIC and recently experienced several issues that all appeared on the same day.

Here’s what’s happening:

• Shuddering during slow turns, both in reverse and forward. This happens around a 3/4 steering turn, not at full lock.
  
• While driving straight, the car feels like it has a slight “humping” sensation. This becomes worse as speed increases and turns into a vibration past 50 mph. It’s not violent, but the rhythm feels tied to wheel rotation, almost like a tire flat spot.
  
• Every time the car shudders during slow turns, the brake pad wear warning comes on immediately. Scanning shows the right rear pad sensor. Visually, the inner side of the right rear rotor is rusted.
  
• There are no abnormal noises at any time — no humming, squeaking, clicking, or grinding.
  

I brought the car to a shop, and the two mechanics there had different opinions.

• Mechanic #1 believes the right rear rotor is rusted and that the parking brake may not be releasing properly, causing the wheel to bind during slow turns.
  
• Mechanic #2 disagrees. He pointed out that the rear wheels don’t steer, and if the pad sensor were truly bad, it should trigger consistently — not only during turns and shuddering. He’s more suspicious of a rear differential issue.
  

To test further, they tried to recreate the shudder by shifting the car into Neutral and letting it roll. The car still shuddered while in Neutral, so they believe it’s unlikely to be the transfer case or transmission, since those should be disengaged in Neutral (though I’m not fully clear on what exactly is disengaged).

Has anyone experienced something similar?

I know many people have reported low-speed shuddering issues, but I haven’t found any cases that also include the brake warning behavior and vibration symptoms I’m seeing — especially with everything happening all on the same day.

One more thing worth mentioning: during a few extremely cold days last week, the humping sensation completely disappeared, and the shuddering was almost nonexistent when temperatures were very low.

Any insight or similar experiences would be greatly appreciated.

 

Did any of them read out any current or stored wheel speed sensor code?

 

They told me they only find the right rear brake sensor code but nothing else. and visually inspect the right rear inner surface of rotor is badly rusted, mechanic 1 say it could be rubbing due to the rusted rotor and suggest new pads and rotors, and mechanic 2 does not really agree because he thinks the rear wheel don't turn and if the rusted or seized rear brakes are grabbing it it should grab all the time why only at turning. Also, the brake pedal did not have any ABS trigger feeling when the shudder happens.

 

Well, in this case, you need to let them slap four new discs and pad sets on the car and see if the problem follows. Sounds like it’s time for a brake job anyway.

 

Rusty brake rotor surface means the pad is not even touching the rotor so there may be some bigger issue with the brakes.

You likely have separate issues with brakes and the rest of your story.

You need better mechanics. The rusty brake rotor should have told them what I just said. What comes to letting car to roll on neutral your transmission still turns with the wheels turning against the road surface. It is not disconnected, it just is not transmitting power, but there are a whole bunch of parts rotating.

For me it sounds you have the familiar transfer case problem and the brake issue is separate from that.

 

At this point, they’re suggesting replacing the rear rotors and pads and doing a rear differential fluid change. We already did a full front brake replacement last week ( rotors, pads, caliper, fluid flush)

Both mechanics test-drove the car and don’t believe it’s the transfer case. The car drives perfectly fine overall—shifts smoothly, no shuddering at any speed, and no vibration or noise on the highway. They even took it up to nearly 100 mph on a stretch of highway and said it was completely stable.

The only issue is the “flat tire spot” feeling. They explained that this sensation matches wheel rotation rather than a transfer case issue. According to them, if the transfer case were failing, the shuddering would be much more violent and would show up more consistently, especially at low speeds. They also mentioned that components inside the transfer case (gears or clutch packs) rotate faster than the wheels, so a fault there wouldn’t feel subtle or intermittent like this.

They still also cannot figure out why the right rear pad wear sensor light comes on every time it shudder at slow turns, is really unrelated but the car make us thinking is somehow related.

I’m not very knowledgeable when it comes to mechanical details, so I’m relying on their explanation. Both mechanics are Mercedes-Benz certified and previously worked at the local MB dealer before opening their own shop, the mechanic that suggest is the rear diff is the master mechanic there. so I’m not sure where else I could realistically go for another opinion.

 

propshaft centre bearing

I have suggested the groans could be the diff but no idea about 4x4 rubbish

 

I like this answer

 

You said in your original post it happens at low speed turns. Turning the car makes difference between front and rear axles meaning you have speed difference what the center differential has to allow between the axles. Otherwise you would have the problem that some old 4-Wheel driven cars have where the front and rear axles fight and make one axle slip. This is why 4-wheel cars should never be driven with 4-wheel drive engaged on dry pavement. The transfer case or other drive line components could break especially if car has plenty of load.

Mercedes $Matic is an All-Wheel drive system with built-in center differential that allows speed difference between front and rear axles so the axles don't fight under the turn that generates the speed difference. This construction also includes a lock that allows one axle to pull the car forward when other is on slippery surface. This lock, at leasi in some models, is a spring loaded clutch and this clutch can experience a "Stick-Sliop" condition especially during slow speed turns where the clutch tries to hold but then releases, which causes the "jerking" of the car as the transmission componentrs are steel and act as springs under load.

I do not know what type your center differential lock is but if it is about the "SAtick-Slip" you could perhaps help it by "cleaning" the friction surfaces by just driving the car for a few minutes in a circle on an empty parking lot or similar open space and see if it helps. This does not cause anything.

You definitely need brake job, but ask them star mechanics why the brake rotor on one side is rusty? This means the pad is not coming toi contact with the rotor surface and this should not be just a pad/rotor issue.

Be careful with your mechanics that they don't fool you to do some expensive repair you don't need. They learned that game well if they indeed were working for MB dealership in the past.

 

Not the car to speculate or throw parts at. There are a ton of electronic systems and nanny controls to keep these things functional. Like an F-16 or any other advanced fighter jet, they're all fly-by-wire (as these cars are drive-by-wire), and so without the computer systems the planes couldn't even fly. These cars have so many electronic systems you really have to pull codes before anything else. These cars even have electronic braking interventions that occur when the car senses cross-wind, and will apply light braking to the opposite side to counter the wind force keeping the vehicle tracking straight. Yes, these are old cars now, but the tech was about ten years ahead of everyone else at the time and is still nuts.

If it's visually obvious, however, such as your rusty rotor, then obviously you don't need a computer to tell you it needs regular maintenance.

 

To be honest I would love to have a RWD but where I live it has been snowing basically every single day for the past two months and I also live on a hill I have owned several RWD cars before and in these conditions they are pretty much undrivable even with a good set of winter tires

The two mechanics are solid and I do not have any trust issues with them Realistically I only use the car to go to and from work so if it starts turning into a money pit I will probably just drive it as is until it is done Right now the car is still good overall aside from the shuddering

I am going to do the brakes for sure and I will also do the front and rear differential fluid at the same time I am not really keen on spending another 800 right now on a transmission and transfer case service so I am hoping either the brakes or the diff fluid takes care of it

The front CV axles were replaced last year so I can pretty much rule that out It may need engine mounts as well I have read they are a pain to change on a 4MATIC but I do not think engine mounts would cause these symptoms unless they were completely collapsed If that were the case I would expect vibration throughout the entire drive not just what I am experiencing now?

 

If the disc is rusty on one side then you have at least one frozen piston on that side of that caliper.

Pull the pads and check and replace what you find. If you do need a caliper, replace the brake hose too.

Just been through this on my 133k mile 2006 S500. Went to push the pistons in to fit the new pads and one pistons was frozen solid. Zero sign of any issues under normal use. New calipers and hoses in addition to the disc and pad change.

You may find the noise is the result of lateral loads forcing the disc into the pad. The light will be on for a reason and if the inner face of the disc is rusty it won't run smoothly over the pad so could be the cause of the jerkiness.

Start with a brake service before you get stuck into the trans or diffs.

 

Go drive a circle in an open area to clean the center differential lock disk surfaces as this could very well be the source for vibration you feel. This is free troubleshooting step and has helped others with the issue.

Some people have done this by jacking up one front wheel and then running the car with that one wheel spinning, which forces the center differential lock to rotate disk surface but this is a very harsh method. A better/safer one is just to drive the car in a circle.

 

I actually did that last week for around 3 to 4 minutes and didnt help, only to trigger the brake pad wear light again.

 

brake pad warning light is nothing - its just a basic connection of a bit of wire rubbing on the pads it means almost nothing

seized brake pistons in merc calipers is a modern speciality most brand employ,

rusty inside faces of front discs is an attribute of V engines parked out side - and I can image also an indicator at the rear of a hot disc sweating from a seized claiper

Limited slip diff groan all day long

 

OP you have been inundated with various advice here - go do a brake job and see if the issue persists.

 

Yup I booked a full rear brake job and front rear diff fluid change this coming week, hopefully it will sort it.

Another question is about the diff fluid I know the rear uses 85W90 according to the manual but how about the front? I found many instruction on how to change it but nobody mention if it uses the same fluid as the rear.

 

The W164/251 suggests different MB specs, but the gear oil is the same.

The viscosity you give above is different to the W164, but the principle is probably the same...

 

Yeah the W164 has different spec, I am just wondering if the front and rear uses the same spec since nowhere on the manual or tutorials say about it, so I assume I can use the same for the front diff as the rear does?

 

That was the point I was trying to make... That both diffs probably use the same fluid, not that it should be the same spec as the W164😉

The ONLY reason they might use different fluids would be if the rear is limited slip and the front is not...

Actually looks like it's the same fluid and the spec you gave is wrong.

https://operatingfluids.mercedes-benz.com/sheet/231.1

Rear axle is 235.7, front is 235.74. Both use 75w85. Which is in fact the same as the W164... Fuchs Titan Sintopoid FE 75w85.

https://operatingfluids.mercedes-benz.com/sheet/235.7

 

[QUOTE=msiumng;9268227]Hello everyone,

I have a 2009 S450 4MATIC and recently experienced several issues that all appeared on the same day.

Here’s what’s happening:

• Shuddering during slow turns, both in reverse and forward. This happens around a 3/4 steering turn, not at full lock.
  
• While driving straight, the car feels like it has a slight “humping” sensation. This becomes worse as speed increases and turns into a vibration past 50 mph. It’s not violent, but the rhythm feels tied to wheel rotation, almost like a tire flat spot.
  
• Every time the car shudders during slow turns, the brake pad wear warning comes on immediately. Scanning shows the right rear pad sensor. Visually, the inner side of the right rear rotor is rusted.
  
• There are no abnormal noises at any time — no humming, squeaking, clicking, or grinding.
  

I brought the car to a shop, and the two mechanics there had different opinions.

• Mechanic #1 believes the right rear rotor is rusted and that the parking brake may not be releasing properly, causing the wheel to bind during slow turns.
  
• Mechanic #2 disagrees. He pointed out that the rear wheels don’t steer, and if the pad sensor were truly bad, it should trigger consistently — not only during turns and shuddering. He’s more suspicious of a rear differential issue.
  

To test further, they tried to recreate the shudder by shifting the car into Neutral and letting it roll. The car still shuddered while in Neutral, so they believe it’s unlikely to be the transfer case or transmission, since those should be disengaged in Neutral (though I’m not fully clear on what exactly is disengaged).

Has anyone experienced something similar?

I know many people have reported low-speed shuddering issues, but I haven’t found any cases that also include the brake warning behavior and vibration symptoms I’m seeing — especially with everything happening all on the same day.

One more thing worth mentioning: during a few extremely cold days last week, the humping sensation completely disappeared, and the shuddering was almost nonexistent when temperatures were very low.

Any insight or similar experiences would be greatly appreciated.[/QUOTE
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DEJAVOUS! From Dec, 2024 to July 2025, I went through hell with the exact same shuddering with my 08 S550 4 MATTIC and spent $3500 with no resolution to shudder. Mercedes has a name for it, "Juddering". On cold days, especially snow, shudder was not there. Juddering is caused by tires scrubbing like an old American pickup truck with locking 4 wheel drive hubs going around corners.

Miss diagnosis' included: * flush front diff: * pull front left CV axle & intermediate axel to inspect bearing. * flush transfer case, * flush rear differential and finally replace rear axel.

I paid $15,000 for the car in 2022 and was so frustrateed at one point, I considered a Carvana offer to buy it for $2500. I live in Michigan and kissed a lot of frogs in 2022 before buying in Chicago from a master mechanic who trained and worked for 20 yrs in a Slavic county then and came to the US 8 yrs ago to open his own one-man shop in Chicago (3 hr drive from me). I tried to reach him during my frustration but he was in Europe for a month due to a family funeral. When he came back I spoke with him and he said to bring it to him. By then, I was afraid to drive it and paid to have it transported.

He determined it had the wrong transmission fluid (tranny and trasfer case use common fluid). It's supposed to have some stuff to make transfer case clutches work better. I didn't know it at the time but in 2022 it had a tiny trans drip from the trans pan gasket. This meant replacing the gasket and new (WRONG) fluid. It took till 2024 to develop the shudder. This wrong fluid had messed up the clutches in the transfer case and residue got into valve body and affected the TCU. (conductor plate).

He drained, cleaned valve body and flushed it several times and sent the conductor plate to one of the people who do module repair. He then drove (20 miles) it back and forth from home to shop for two weeks. I took a train to Chicago and drove it home July 3 and celebrated July 4th with no shudder. It's been fine since. Through all of this, was thoroughly pissed at multiple local shops that screwed me because they didn't know what they were doing. It would be nice to have someone good locally and suggessted to "Igor" he move his shop to Michigan but with family, etc it wouldm't work.

 

well I have no idea the spec is from the owners manual of my car

 

[QUOTE=EURO-JIM-121;9270576]Wow, thanks for the input. I still don’t know exactly what’s going on with mine yet, but over the past few days as the weather has gotten warmer the feeling seems a bit different. It doesn’t really feel like a shudder anymore. It’s more like a vibration that matches the wheel rotation.

The best way I can describe it is that it feels exactly like when a wheel is bent or a lug is loose and the car starts to wobble slightly. I have already checked the wheels and lug nuts though and everything looks fine.

The “humping” or wobbling sensation seems directly related to vehicle speed, almost like one of the wheels is not perfectly round. It is not violent at all and there is no rubbing sound or unusual noise. It is just that subtle vibration that increases with speed.

I have owned the car for about three years and driven roughly 20,000 miles without any issues like this. The problem only started about three weeks ago and seemed to appear all of a sudden.

So do you mind saying how much at the end the shop charge for the transmission work to get it back to life?

 

In that case either go with the manual or ask MB...🤷

Have you fixed the brakes yet?

 

I wasn't aware they might have done it wrong on other models - but a recent GLC 4 x4 has mega suspension / steering geometry issues -

basically Merc have no clue how to design a safe / roadworthy car - and thus some 4 x 4 models have seriously compromised steering geometry - because they never bothered to design the car for both LHD and RHD markets

BMW design all their 4x4s to drive correctly on both sides of the road - but Merc never bothered to think about it and thus can't have the correct geometry to make the Ackerman principle behave - so the wheels are misaligned and the tyres have to fight each other and skip / hop / judder to try and behave on large corners

the Merc issues flew around the internet and Mercs rush job technical solution was to offer a set of soft compound winter tyres so they can deform and judder more quietly !!!

this video provides plenty of footage about the issues for the driver - but all his attempts to flim the tyre dragging over the surface tearing the tread blocks to bits and the suspension trying to fall off as the whole set up judders are truly pathetic