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Yesterday when driving running errand I heard a single thump from the rear of my car when turning. At first I thought I had something rolling around the trunk of the car but unfortunately not. What I hear is a single somewhat muted thump when I make a turn. It always happens turning right. I'd swear I heard it turning left but it does not do it every time so not sure. It is not loud and it happens only once during the turn. I do not notice any performance issues. The turn has to be fairly sharp like turning right from a stop sign or light. It does not happen driving down the road in a curve. It does not specifically seem to correspond to acceleration in that I accelerate to get moving but then coast a bit through the turn. It seems to me it happens more on the coast than on the acceleration.
This is a rear wheel drive car. Any idea what items I should be checking?
I would jack the rear end up, remove the wheels and have a look around. Inspect all the control arm attachment points on the subframe for rust/wear. Inspect the tire tread wear, see if its wearing evenly. May be a worn control arm bushing, but im just guessing at this point.
Took the right rear tire off and see a little more worn on the inside. Visually everything looks solid and no cracks in various boots. I am not sure how to inspect the subframe but I will look that up. It just seems odd to me that the noise happens only once during the turn and not at least somewhat continuously.
So unfortunately I can now get it to happen in general. I made this terrible video but hopefully it helps. Visually everything looks great but I have not started pulling anything apart yet.
Watching the video i see the passenger side axle appearing to rotate while the drivers side is not (its rotating just not consistently guess id say). When the noise happens it seems to coincide with the drivers side axles rotation.
is the noise coming from wheel assembly area, or is it coming from the differential?
It looks to me like when the thump occurs the drivers axle stops briefly. Like its getting bound up on something.
With both rear wheels off the ground and tires still on spin one of the wheels by hand, the opposite wheel should/will spin the opposite direction. Listen closely for any noise, see if the brakes are rubbing, or if you can hear anything coming from the differential. Take the wheel and spin it so the other wheel starts spinning then stop it quickly, see if theres any odd noises. Take the wheels off and do the same, may be able to feel where the noise is coming from.
I tried what you suggested and really did not hear what I think was 'the' noise. I have the car jacked up in a more permanent way today so I may try another video and get further under it. When I made the video it definitely seemed to me the noise was from the area of the differential. So if axle vs differential I suspect on the differential end. No idea how to determine which.
There is a little play between the differential and the shaft coming from the front of the car. As in, when I turn the wheel there is about a second before the the shaft turns and that make a small clunk. Maybe that is important and maybe it is not. I don't think the noise it made was concerning per se so much as possibly any play between starting turning the wheels and it turning the shaft.
Interestingly I can turn the wheels when the car is in park. So I think there is a potential brake issue there. I do think there is some rubbing from the brakes but it might be time to look at those anyway. I had to change the front brakes and lines a couple months ago.
With both wheels off the ground they should spin freely, opposite wheel spinning in the opposite direction. I dont know all the mechanics of a differential but its the same on my car. If you have only one wheel off the ground you shouldnt be able to spin the wheel, the other wheel on the ground prevents it from moving.
If the sound may be coming from the differential I would drain the fluid and inspect it for any metal. I used Febi 75W-85 since I can get it locally and it meets the MB specs. I think mine took 1.1 liters so I bought 2 bottles. Need a big H14 hex socket for the drain and fill plug.
So… brought my son out to listen to the noise to see if he agreed with me on the location. Jacked the rear up, he climbed under the car and I revved the engine to make noise which it did. Then we discussed and he asked about traction control being on. We turned it off and revved the engine, no noise. He wanted the hear the noise in general so we drove around for about 40 minutes. No noise with traction control off and on. Basically we could not replicate the original issue.
FWIW, I did go ahead and chains the oil in the differential and saw no metal on the drain plug.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Interesting. Traction control is usually a function of cutting power and applying the brakes to the wheel spinning the fastest. I didn't see if you said you had a Mercedes scanner to check for codes. Have you done that?
That I can handle. I'll read the post more carefully in a bit but that looks like what I really need. Thank you. Although I have to say that I'd prefer something that is not MB specific as I do have another non-MB car and my son uses it too. Though I guess I have the current one for those.
Last edited by jeiholzer; Sep 26, 2024 at 10:08 AM.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by jeiholzer
That I can handle. I'll read the post more carefully in a bit but that looks like what I really need. Thank you. Although I have to say that I'd prefer something that is not MB specific as I do have another non-MB car and my son uses it too. Though I guess I have the current one for those.
The first one is what you want (LAUNCH Creader Elite 2.0 BENZ). The rest of the thread is just more information.
I have tried more scanners than I care to admit, and the LAUNCH Creader is my keep-in-the-car, go-to scanner. I have the Autel MaxiDAS DS808, BlueDriver, iCarsoft MB II, iCarsoft MB v3, LAUNCH Creader Elite (1.0) BENZ, LAUNCH Creader Elite 2.0 BENZ, and SDS (XENTRY). XENTRY is the ultimate diagnostic tool, but doesn't fit in the glove box very easily (i.e., not at all). I keep my Creader in one of the side compartments in the trunk in my C350 and in the storage behind the driver's seat in my SL400. Yes, I keep one in each car.
That I can handle. I'll read the post more carefully in a bit but that looks like what I really need. Thank you. Although I have to say that I'd prefer something that is not MB specific as I do have another non-MB car and my son uses it too. Though I guess I have the current one for those.
You could rent for a month or a year other brands in their mall.
I read my operators manual on how traction control works and im still confused. From the way I read it if you turn the ESP off the ETS (Electronic Traction System) is still on which will apply the brake to spinning wheels.
From my Operators Manual:
"When you switch off the ESP,
* the engine output is not limited, which allows the drive wheels to spin and thus cut into surfaces for better grip.
* the ETS/4-ETS will still apply the brakes to a spinning wheel."
From the video I would have guessed the drivers side brake is coming on > drivers axle stops briefly > noise occurs.
With traction turned back on, and the drivers wheel off, i wonder if you can see the brake being applied?
Watching the video over and over it appears the passenger axle stops at second 3 and 7. The drive shaft looks like its moving right along. The drivers axle looks like its struggling to even move. What does this mean, no idea.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by TimC300
I read my operators manual on how traction control works and im still confused. From the way I read it if you turn the ESP off the ETS (Electronic Traction System) is still on which will apply the brake to spinning wheels.
From my Operators Manual:
"When you switch off the ESP,
* the engine output is not limited, which allows the drive wheels to spin and thus cut into surfaces for better grip.
* the ETS/4-ETS will still apply the brakes to a spinning wheel."
From the video I would have guessed the drivers side brake is coming on > drivers axle stops briefly > noise occurs.
With traction turned back on, and the drivers wheel off, i wonder if you can see the brake being applied?
Watching the video over and over it appears the passenger axle stops at second 3 and 7. The drive shaft looks like its moving right along. The drivers axle looks like its struggling to even move. What does this mean, no idea.
ESP is a vehicle stability and vehicle control function to bring the car in line with the direction of travel during a skid or such. This is accomplished by applying brakes individually and "modifying" engine output. ETS, on the other hand, appears to enhance traction on a slippery surface to move the car forward. Both use the brakes to control the car or wheelspin. I think that is why in the engineering menu there is a dyno mode since disabling ESP does not disable ETS. The dyno mode probably further disables ETS.
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