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2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by TimC300
I have a washer on the smooth pulley, its on the inside between the pulley and the engine. Strange that I do not see this washer on any parts diagrams though.
In typical Mercedes fashion, you probably have to buy the entire engine to get the washer. (Or maybe just the pulley.)
I wont have my car until Monday so I cant check mine. But from my photos it does look like there is a small space between the front face of the belt and the front leg of the smooth pulley. You can remove your smooth pulley and look for any abnormal wear on the inside face. On my old smooth pulley i did not notice any abnormal wear. But then again i do have that washer installed on the back of the pulley.
Where does your tensioner marks line up? Maybe take a photo, like i posted of mine above. It should be within the two guide marks.
What exactly do you have installed for the grooved pulley? because you mentioned some spacer in a tsb.
Post #5 you mention black paint rubbed off the smooth pulley, do you mean its worn off on the smooth surface that the belt rides on? Because that is normal, can see the pain worn on my old pulley as well.
Here is the picture of markings on my tensioner. It is in the middle of the two markings. I installed a 1 mm spacer behind the lower guide pulley just like the TSB states but upon startup it was constantly squeeling. I had to remove it again. I don’t understand the issue with my car.
"Here is the picture of markings on my tensioner. It is in the middle of the two markings. I installed a 1 mm spacer behind the lower guide pulley just like the TSB states but upon startup it was constantly squeeling. I had to remove it again. I don’t understand the issue with my car."
Then you have a lateral belt lineup issue. The belt must be running against a pully shoulder. The edges if the belt should not be worn or it is out of "track".
It is possible that the alternator clutch pully was replaced with the wrong part and hence the wrong offset.
In the photo above I notice some lines on the smooth side of the belt, I dont see the same when I look at the photo way above of my belt and ive had mine installed well over a year now. Are those wear marks, frays? I cant tell.
I just finally opened up that TSB to see what it said. It says to basically look at the pulley on the belt tensioner and use that as a guide to set the idler pulleys, if a shim is needed. On my smooth pulley i have a regular washer back there, its not a recommended shim, id say my washer is 3mm. Then I look at my photo of the tensioner pulley and I can see the wear marks and my belt looks to be running a bit too forward, but ive had it like this without issue to im not going to touch it.
When I zoom in on the photo above of the belt tensioner it looks to me that the belt is in the correct position, or maybe a little forward. It does not look like it needs a shim on the smooth pulley at least.
In the photo above I notice some lines on the smooth side of the belt, I dont see the same when I look at the photo way above of my belt and ive had mine installed well over a year now. Are those wear marks, frays? I cant tell.
I just finally opened up that TSB to see what it said. It says to basically look at the pulley on the belt tensioner and use that as a guide to set the idler pulleys, if a shim is needed. On my smooth pulley i have a regular washer back there, its not a recommended shim, id say my washer is 3mm. Then I look at my photo of the tensioner pulley and I can see the wear marks and my belt looks to be running a bit too forward, but ive had it like this without issue to im not going to touch it.
When I zoom in on the photo above of the belt tensioner it looks to me that the belt is in the correct position, or maybe a little forward. It does not look like it needs a shim on the smooth pulley at least.
The white marking you see on the edge of the belt is the white lacing or whatever you call it. Everything seems like it’s in line but I do see the belt wobbling around. Let me see if I can record a video of it. Do you need a picture of the grooved idler pulley?
Your belt is wobbling? I had changed my belt and tensioner because the belt looked like it was bouncing, then i looked at the tensioner and the arm looked like it was going up and down, like it was riding on the belt then dropping back into place. Replacing the tensioner solved that issue.
a worn/bad harmonic balancer would made sense. Take some close up photos of it and look at them on the computer. Thats how i usually look at things to see better.
I went out and looked at mine again, it looks like my belt is right where it should be as far as lining up on the tensioner pulley. Can see the wear marks on the outsides of the pulley and they look even, belt is riding in the middle. I recently had my car worked on and not sure if they had removed the smooth idler pulley, if they messed with the washer.
I also checked the back side of the belt and do not see any abnormal wear.
a worn/bad harmonic balancer would made sense. Take some close up photos of it and look at them on the computer. Thats how i usually look at things to see better.
I went out and looked at mine again, it looks like my belt is right where it should be as far as lining up on the tensioner pulley. Can see the wear marks on the outsides of the pulley and they look even, belt is riding in the middle. I recently had my car worked on and not sure if they had removed the smooth idler pulley, if they messed with the washer.
I also checked the back side of the belt and do not see any abnormal wear.
I attached a video of my belt having a slight side to side movement. I don’t know if that is normal. I also have not tried putting the 1mm spacer behind the grooves pulley after installing this new tensioner. What I don’t understand it that if I put a brand new belt on, then there is no belt chirp or any noise until the belt wears down a little bit with around 1000 miles. Were there more tsbs released to address this issue by Mercedes?
Try this. Get one of your old belts out that isn't worn on the edges. Using white paint, paint a thin border on top of the belt to leave a line/border (maybe 1/8 inch wide) on the upper flat side of the belt right on the edge.
Install and run the engine. Then you'll be able to visually detect any component that's possibly out of alignment as you'll see the white line move as it passes each component. It's important that the white line is consistent so use some tape to mark it and keep the paint out of the grooves on the underside.
Hope this helps.
Last edited by BlackML550; Nov 8, 2024 at 07:36 AM.
Has me screaming at the video to stop moving. I tried to focus in on one pulley at a time but the camera keeps moving around.
Above you mention having a shim at the GROOVED pulley? The notice for the shim refers to the SMOOTH pulley only.
Have you gone through the procedures outlines in the bulletin, measure the location of the belt on the tensioner pulley?
What I was able to notice is the tensioner appears to be really moving up and down. I dont think mine is like that, I think mine is smooth with hardly any movement. Ill have to double check. I tried to focus in on the crankshaft pulley to see if that is wobbling, couldnt really tell.
I also noticed the belt wear marking is all the way near the end, at the line that shows it should be replaced? What size belt do you have on there?
Has me screaming at the video to stop moving. I tried to focus in on one pulley at a time but the camera keeps moving around.
Above you mention having a shim at the GROOVED pulley? The notice for the shim refers to the SMOOTH pulley only.
Have you gone through the procedures outlines in the bulletin, measure the location of the belt on the tensioner pulley?
What I was able to notice is the tensioner appears to be really moving up and down. I dont think mine is like that, I think mine is smooth with hardly any movement. Ill have to double check. I tried to focus in on the crankshaft pulley to see if that is wobbling, couldnt really tell.
I also noticed the belt wear marking is all the way near the end, at the line that shows it should be replaced? What size belt do you have on there?
thanks for the reply. I installed the shim on the smooth pulley but the belt squeals like crazy when the engine is running so I am forced to removed it. I have tried the shim on the grooved pulley with the old tensioner and it was doing the same thing. I have not tried it after installing this new tensioner. The belt was changed over the summer and it has less than 5,000 miles on it. I have the 2397mm Mercedes belt installed on it. Again, brand new belt fixes the problem for like a short period of time.
The marking on the tensioner is at the center of the two lines when the engine is off. I have noticed that it’s all the forward when engine is running until you pointed that out.
Since you see the tensioner peg to one line when running. See if that line is for full tension or no tension. I dunno the direction but you would have to exercise the tensioner to see.
Another question would be when you put the belt on does it fit easily on our do you barely have enough room to get it on?
I ask because maybe the belt can be replaced with one smaller or larger if the tensioner is pegged out. You can get belts just based off the length. It isn't ideal but you have tried so much already this crossed my mind because I made many trips to get slightly longer belts to fit my race car.
Since you see the tensioner peg to one line when running. See if that line is for full tension or no tension. I dunno the direction but you would have to exercise the tensioner to see.
Another question would be when you put the belt on does it fit easily on our do you barely have enough room to get it on?
I ask because maybe the belt can be replaced with one smaller or larger if the tensioner is pegged out. You can get belts just based off the length. It isn't ideal but you have tried so much already this crossed my mind because I made many trips to get slightly longer belts to fit my race car.
I have tried the Mercedes 2390mm on my car but it still had the issue but that was with my old tensioner. I haven’t tried that belt again with the new tensioner.
Since you see the tensioner peg to one line when running. See if that line is for full tension or no tension. I dunno the direction but you would have to exercise the tensioner to see.
Another question would be when you put the belt on does it fit easily on our do you barely have enough room to get it on?
I ask because maybe the belt can be replaced with one smaller or larger if the tensioner is pegged out. You can get belts just based off the length. It isn't ideal but you have tried so much already this crossed my mind because I made many trips to get slightly longer belts to fit my race car.
I tried everything you recommended. The line to the right on the tensioner is full tension and the one to the left is no tension. The picture you with marking I posted earlier was with the Mercedes 2397mm belt installed. I removed that belt and installed the Mercedes 2390mm belt. It was fine for a day or so and then after the car sat outside for 10 hours with temps around 30 degrees, upon startup the belt was making so much sound. The belt will not quiet down until engine reaches operating temp whereas before it would stop like 2 minutes after start. I looked at the markings while the engine was running and the marking was all the way to the left now. I don’t understand how a small belt is loose on the pulleys while the bigger belt has better tension. I exercised the tensioner as well.
I was curious how much my tensioner moved with the engine running so just went out to check. The marking on the tensioner doesnt seem to move much with the engine running.
I was curious how much my tensioner moved with the engine running so just went out to check. The marking on the tensioner doesnt seem to move much with the engine running.
engine not running:
Engine running:
the markings don’t move much either on my car regardless of the engine is running or not. Right now what I found is that putting a smaller belt is loose and making so much noise compared to the 2397mm
The tensioner only moves on excel or decel so revving the engine it will move some.
Makes no sense why a smaller belt would make more nose unless we're not dealing with a belt squeal and a bearing squeal instead.
But I know you've checked all that so I'm at a miss what to try next.
The tensioner only moves on excel or decel so revving the engine it will move some.
Makes no sense why a smaller belt would make more nose unless we're not dealing with a belt squeal and a bearing squeal instead.
But I know you've checked all that so I'm at a miss what to try next.
yeah I don’t know what to do either. What size belt do you have on there in mm. I have a 2404 mm continental belt that I might try but for now I’m just gonna install the 2397 mm belt back on since true belt quiets down after couple minutes compared to this one that just noisy and embarrassing.
Hi all, I just stumbled on this thread and believe I am experiencing the same issue with my 2010 X204 GLK 350. Have you found a resolution to this yet?
I replaced both idler pulleys, the tensioner, and the belt. No issues after installation, but about 1k miles later a nasty squeak manifested from the lower (smooth) idler pulley (brand was OEM INA from FCP Euro, so not Genuine Mercedes). Along with the squeak, I also noticed the same belt side to side alignment issue when spinning (not sure if it's the pulley runout, alignment, or belt). Thinking it may have been a defective pulley, I requested a replacement part. Lo and behold, a different sounding clunking noise was still there with the pulley. I've documented my issue in the thread below in the X204 forums.
Would be interested as I replaced my belt and 1.5 months later it squeaks in cold weather like 0 Celsius or 32F
You need another new belt and this time include a new tensioner.
Test every accessory pulley during sce. One may be failing (ALT, PMP, A/C, ...)
Squeaking is the advanced phase of slipperiness. Friction heats up belt that gets hot and shreads then engine overheats with stopped cooling... Tow truck + head gasket job is the wrong way towards savings.
HK/CN cross border plates: luxury S320 under powdered
Last edited by CaliBenzDriver; Nov 24, 2025 at 05:03 AM.
You need another new belt and this time include a new tensioner.
Test every accessory pulley during sce. One may be failing (ALT, PMP, A/C, ...)
Squeaking is the advanced phase of slipperiness. Friction heats up belt that gets hot and shreads then engine overheats with stopped cooling... Tow truck + head gasket job is the wrong way towards savings.
HK/CN cross border plates: luxury S320 under powdered
Squeal ONLY when engine is cold 0 Celsius or 32F. Not the temperature you would expect in HK or north of HK. Not squeak when engine hot say after 10-15minute driving.
Last edited by petaling; Nov 24, 2025 at 07:22 AM.
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