SL/R230: Single thunk after startup, not engine
Thread Starter
Senior Member
Joined: Jan 2009
Posts: 337
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From: Montrose, CA
2007 SL550
Single thunk after startup, not engine
Hi, folks, when I start my 2007 SL550 in the morning, it makes a single loud THUNK a couple of seconds after the engine catches. It sounds like it comes from behind me, not in front of me, so I don't think it's coming from the engine.
It was too sporadic for the dealer to hear it until today when I was driving on vacation (of course) and when I took it in to another place, they said it was a normal sound from an older transmission. (My car has 275,000 miles on it. I'm aiming for a million.) I find that hard to believe, as it sounds like someone whanged the underside of the car with a rubber mallet. It's startlingly loud.
Has anyone had a similar experience?
Thanks,
Michael
It was too sporadic for the dealer to hear it until today when I was driving on vacation (of course) and when I took it in to another place, they said it was a normal sound from an older transmission. (My car has 275,000 miles on it. I'm aiming for a million.) I find that hard to believe, as it sounds like someone whanged the underside of the car with a rubber mallet. It's startlingly loud.
Has anyone had a similar experience?
Thanks,
Michael
MBworld Guru
Joined: Dec 2009
Posts: 10,782
Likes: 1,011
NO LONGER ACTIVE
Wow, that's some serious miles on the R230! How has it been in terms of maintenance?
As for the sound, I don't have much to offer, but maybe it's exhaust related? At that mileage, your cats are likely dead.
As for the sound, I don't have much to offer, but maybe it's exhaust related? At that mileage, your cats are likely dead.
Thread Starter
Senior Member
Joined: Jan 2009
Posts: 337
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From: Montrose, CA
2007 SL550
I feel like I've been lucky. She's had the usual SL problems - replaced the ABC/steering pump a couple of times, had 3 hydraulic lines blow over that time, replaced both accumulators, a sensor here and there, countless tires ;-). But the engine and transmission are still purring nicely. No body rattles. Then again, this is kinda a love affair I've got, and what would be annoying in a stranger is endearing in the ones you love, so I may be forgetting some things.
Right now she's getting into uncharted territory. None of the techs have worked on an SL with this many miles. ;-) This noise has stumped them, too.
What worries me is that I've had two serious hydraulic issues seconds after this thunk, which has me wondering if one of the valves in the valve blocks is sticking. Thankfully the impacted parts were srill under warranty. But nobody is willing to open up those boxes on an off chance, and I can't really blame them.
Last edited by mlandis; Oct 6, 2016 at 01:28 PM. Reason: Adding color
Thread Starter
Senior Member
Joined: Jan 2009
Posts: 337
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From: Montrose, CA
2007 SL550
I'm pretty sure they're fine. The noise is only at startup, no other time, and doesn't seem tied to the actual engine startup. It was also quite inconsistent to begin with, only appearing every few days or once a week, but whenever it did happen, it was the same loudness. It's only recently that it's happening consistently. So it hasn't been a gradual increase in severity, or a sudden start of the issue, which is how I'd expect the flex discs to go.
Last edited by mlandis; Oct 6, 2016 at 01:20 PM. Reason: I was repeating myself
Senior Member
Joined: Mar 2010
Posts: 451
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2007 E350; 2018 GLE350
Lemme ask one more question, Mate: I'm assuming you go to your car, open the door, get seated, then start the engine ... and then you hear the clunk.
Have you tried just getting in the car and just sitting there ... not starting the engine ... to determine whether something in the suspension might be making the thunk sound?
Have you tried just getting in the car and just sitting there ... not starting the engine ... to determine whether something in the suspension might be making the thunk sound?
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Joined: Jun 2014
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From: Chandler, AZ
2003 SL500, 2016 ATS, 2016 CTS 2015 Volt
I wonder about that as well since as soon as you start the engine the ABC pump starts pumping and pressurizing the system. If you are still in park, no parts of the driveline will see any rotation or torque.
Last edited by next2pool; Oct 6, 2016 at 10:32 PM.
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Thread Starter
Senior Member
Joined: Jan 2009
Posts: 337
Likes: 0
From: Montrose, CA
2007 SL550
I haven't done a specific test, but I know I've done different things before starting - plugging my iPod in, settling in, and it's consistently 2 seconds after start.
Thread Starter
Senior Member
Joined: Jan 2009
Posts: 337
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From: Montrose, CA
2007 SL550
That's my thinking, too. The timing, plus the fact that it sounds like rubber against metal, not metal against metal or an explosion, makes me think a valve O-ring is sticking somewhere, then popped by the pressurizing of the system.
I'm hoping someone can say "Oh, yeah, that happened to me" that I can take back to the tech.
I'm hoping someone can say "Oh, yeah, that happened to me" that I can take back to the tech.
Last edited by mlandis; Oct 7, 2016 at 09:21 PM.
Senior Member
Joined: Mar 2010
Posts: 451
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2007 E350; 2018 GLE350
Have you tried turning off ABC at the console sometime while driving the car. Leave it off when you shut down the engine. Then see if there's any change the next morning when you start up and shift into gear. I'm now with Italian Joe ... it's something in the ABC, including the struts.
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Joined: May 2015
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From: Miami, FL
2003 CL 600
You can't "turn off" ABC, the pump is hydraulic and runs all the time when the engine runs.
I'd bet you have something in the rear valve block or pulsation damper that's failing.
On my CL, the suspension won't adjust until you move the car, I assume the SL is the same, so I don't think it releases the valves right away. But the system does pressurize as the motor starts, which sounds plausible in your situation.
I'd say have it on a lift when you start it and have someone try to localize the noise underneath.
I'd bet you have something in the rear valve block or pulsation damper that's failing.
On my CL, the suspension won't adjust until you move the car, I assume the SL is the same, so I don't think it releases the valves right away. But the system does pressurize as the motor starts, which sounds plausible in your situation.
I'd say have it on a lift when you start it and have someone try to localize the noise underneath.
Member
Joined: Jun 2014
Posts: 238
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From: Chandler, AZ
2003 SL500, 2016 ATS, 2016 CTS 2015 Volt
You can't "turn off" ABC, the pump is hydraulic and runs all the time when the engine runs.
I'd bet you have something in the rear valve block or pulsation damper that's failing.
On my CL, the suspension won't adjust until you move the car, I assume the SL is the same, so I don't think it releases the valves right away. But the system does pressurize as the motor starts, which sounds plausible in your situation.
I'd say have it on a lift when you start it and have someone try to localize the noise underneath.
I'd bet you have something in the rear valve block or pulsation damper that's failing.
On my CL, the suspension won't adjust until you move the car, I assume the SL is the same, so I don't think it releases the valves right away. But the system does pressurize as the motor starts, which sounds plausible in your situation.
I'd say have it on a lift when you start it and have someone try to localize the noise underneath.
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Joined: May 2015
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From: Miami, FL
2003 CL 600
Interesting, both of my '03 CLs and my friends '03 S600, if sagged down, will only pop back up to normal height if I put them in gear and move a couple inches. I guess the SL is different, I know a lot of the ABC system changes from the 215/220 to the 230 chassis.
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From: Tucson, AZ
'20 X5 M50i; '17 Ram 3500; Golf Cart; Bikes; Scooters
My SL does the same, it levels after moving a few inches, so I'd say the behavior is the same as the CL.
Member
Joined: Jul 2008
Posts: 213
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From: SW Florida
1995 SL500 - 2017 AMG GLC 43
I believe Italian Joe is correct. The rear ABC components are located inside the left wheel-well and suspended with a rubber mount. My car was making a similar (although not as loud) until I changed the Air Reservoir. It only takes a few minutes to remove the wheel-well liner. You can then have someone listen and feel for the clunk. Good luck.
MBWorld Fanatic!
Joined: May 2015
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From: Miami, FL
2003 CL 600
The accumulator? The round black ball?
That would be my guess, it's got air trapped somewhere and as soon as it pressurizes the system, it pops back into there.
As above, gotta gain access and start it with someone checking back there, if it's a loud, repeatable noise, should be simple enough to track down.
That would be my guess, it's got air trapped somewhere and as soon as it pressurizes the system, it pops back into there.
As above, gotta gain access and start it with someone checking back there, if it's a loud, repeatable noise, should be simple enough to track down.
Newbie
Joined: Oct 2018
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2008 CL65
Right, before I shift gears.
That's my thinking, too. The timing, plus the fact that it sounds like rubber against metal, not metal against metal or an explosion, makes me think a valve O-ring is sticking somewhere, then popped by the pressurizing of the system.
I'm hoping someone can say "Oh, yeah, that happened to me" that I can take back to the tech.
I'm hoping someone can say "Oh, yeah, that happened to me" that I can take back to the tech.
Joined: Oct 2019
Posts: 1
Likes: 0
mb c220
Hi, folks, when I start my 2007 SL550 in the morning, it makes a single loud THUNK a couple of seconds after the engine catches. It sounds like it comes from behind me, not in front of me, so I don't think it's coming from the engine.
It was too sporadic for the dealer to hear it until today when I was driving on vacation (of course) and when I took it in to another place, they said it was a normal sound from an older transmission. (My car has 275,000 miles on it. I'm aiming for a million.) I find that hard to believe, as it sounds like someone whanged the underside of the car with a rubber mallet. It's startlingly loud.
Has anyone had a similar experience?
Thanks,
Michael
It was too sporadic for the dealer to hear it until today when I was driving on vacation (of course) and when I took it in to another place, they said it was a normal sound from an older transmission. (My car has 275,000 miles on it. I'm aiming for a million.) I find that hard to believe, as it sounds like someone whanged the underside of the car with a rubber mallet. It's startlingly loud.
Has anyone had a similar experience?
Thanks,
Michael
but i have no clue , never seen anything like it
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Joined: Apr 2006
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From: 33004
2017 X166 GLS550 & (R230) SL550 2007 & 2012 S550
?
The accumulator? The round black ball?
That would be my guess, it's got air trapped somewhere and as soon as it pressurizes the system, it pops back into there.
As above, gotta gain access and start it with someone checking back there, if it's a loud, repeatable noise, should be simple enough to track down.
That would be my guess, it's got air trapped somewhere and as soon as it pressurizes the system, it pops back into there.
As above, gotta gain access and start it with someone checking back there, if it's a loud, repeatable noise, should be simple enough to track down.
I'm pretty sure it is in the ABC system rear driver's side a second or 2 after engine start, without touching the shifter, just sitting in Park.
Last edited by poptopclk; Nov 13, 2024 at 12:18 AM. Reason: add
