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  #16  
Old 12-19-2011, 11:28 PM
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Scientific wild assed guess: Worn crankshaft main bearings. May not have anything to do with these cars whatsoever, but when I was a tech with VW in the air cooled days, they'd develop this resonance noise that sounded like repeated notes on a bass organ at certain speeds and RPMs under load. When I read your post, this was the first thing it sounded like to me- that old VW noise, from many years ago.

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1968 230S Automatic, Elfenbein
1975 O309D Executive Westfalia Camper Bus, Blau/ Weiss
1972 280SEL 4,5 Dunkelrot
1966 VW Type 34 "Grosser" Karmann-Ghia
1963 VW 1500 Variant Pearlweiss
1969 VW Variant Automatic, Perugruen
1971 VW Squareback Automatic, Clementine Orange
2001 E320 4Matic Wagon- Our belated welcome to the 21st century! Polar White
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  #17  
Old 12-20-2011, 12:23 AM
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It's a new engine but it is beginning to resemble the sound my diesel makes when I drive too slow in 4th . it is still pulling but it drums . I shift down a gear and it's fine.
I suspect that the 5th gear is pulling hard at a speed range that is wrong for the engines dynamics . The only cure might be a lower ratio diff. The 5 speed cars from Mercedes always a lower ratio diff than the four speed cars.
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  #18  
Old 12-20-2011, 05:52 AM
GGR GGR is offline
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Thanks all for your input.

Cth350: my 4th is 1:1 and 5th is .875. Noise is not affected by turns or lane changes. The car was on a dyno last Saturday (see my other post in the “outlaws” thread), it’s a shame we didn’t think of tracing the noise. I was not the one operating the car and the guy stayed in 4th. But I’m sure the noise would have been there in 5th at 80mph.

Sjefke: Yes, engine power causes changes in volume but not frequency, but only in 5th and at 80mph. I’ve tried to determine if something in the trans could cause that, but I don’t really see. All bearings are in motion in all gears. If it was a main shaft bearing the noise would be there each time the engine reaches 3000 rpm, in any gear. If it was a secondary shaft bearing the noise would be there at 80mph whatever gear. The only elements that could cause the noise are the 5th gear pinions, but that doesn’t resemble a gear noise? Wouldn’t the noise be there all the time, like a whine with amplitude variations related to rpm while in 5th? I will move my hand along the tunnel and feel whether I sense changes in vibration moving back and forth over the tunnel. But I already noticed I can feel a vibration in the back of the trans tunnel on the passenger side. It’s right behind the flex disc (which is new, genuine MB, big size like on the 560s). I will need to see if that vibration increases when I’m in 5th at 80 mph, and compare with other places on the tunnel.

Tram: a “resonance noise that sounded like repeated notes on a bass organ at certain speeds and RPMs under load”. Yes, this could be a good definition of what’s happening. But if it were related to crankshaft bearings, I guess it would also make the noise under load in 4th, which is not the case.

Mercmad: my rear diff is a 3.27. In 5th it’s equivalent to a 2.85, like on a 6.3. Originally that engine was coupled with a 2.72 rear end, and some 5.0 were even fitted with a 2.24 on some W126s. So I don’t think my rear end ratio is a problem here.

I think Sjefke is putting us on the right track: “if your noise (frequency) is there either way, but worse going uphill and less downhill, then the volume (amplitude) is proportionally to strain/power”. What could cause a frequency to be there in all cases, with an amplitude proportional to strain/power, only in 5th at 3000 rpm and 80mph?

I know engines develop some resonance noise at 3000 rpm. When I was a kid, I’ve seen old school mechanics checking time advance at 3000 rpm just by the sound of the engine, like woom woom woom. This is very easy to do on L6s, but I guess other engines do the same. The noise I’m having in the car is exactly that resonance noise engines do at 3000 rpm, and it is indeed happening at 3000 rpm. But why only in 5th?

Thanks all again for the help.

Last edited by GGR; 12-20-2011 at 06:09 AM.
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  #19  
Old 12-20-2011, 07:02 AM
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I hate to say this but you are pushing too high a gear in 5th and what you are hearing is the engine laboring at point in it's torque curve .
I didn't realise you were running a .875 gear in 5th with a 3.27 diff.


5 Speed equipped mercedes have always run lower ratio diffs for this very reason.
Unless you change the rear end ratio for a lower one,you will always have this resonance.
Because a mercedes engine will live to 6000 RPM without a problem your only option is use 4th until you are hitting 4000 RPM then changing to 5th to avoid the resonance period.
Yes i know 500's run a 2.47 etc diff but they are also using cams which have a lower torque rating and 6.3's have a far longer stoke and bore and can push the 2.82 diff .
You have altered your cam profiles so the torque curve is completely different. AMG 500 stage 1 engines i have driven are hopeless in 4th around town with the same resonance you describe but on the open road at speeds above 100MPH,they come into their own.
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  #20  
Old 12-20-2011, 07:42 AM
GGR GGR is offline
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Quote:
Originally Posted by mercmad6.3 View Post
I hate to say this but you are pushing too high a gear in 5th and what you are hearing is the engine laboring at point in it's torque curve .
I didn't realise you were running a .875 gear in 5th with a 3.27 diff.


5 Speed equipped mercedes have always run lower ratio diffs for this very reason.
Unless you change the rear end ratio for a lower one,you will always have this resonance.
Because a mercedes engine will live to 6000 RPM without a problem your only option is use 4th until you are hitting 4000 RPM then changing to 5th to avoid the resonance period.
Yes i know 500's run a 2.47 etc diff but they are also using cams which have a lower torque rating and 6.3's have a far longer stoke and bore and can push the 2.82 diff .
You have altered your cam profiles so the torque curve is completely different. AMG 500 stage 1 engines i have driven are hopeless in 4th around town with the same resonance you describe but on the open road at speeds above 100MPH,they come into their own.

Hmmm... There may be a bit of this. In the meantime I did a google research with "3000 rpm resonance" and all comments I found incriminate the exhaust system. On a Porsche site they say that if noise amplitude varies with engine load then it is exhaust related. On a BMW 2002 site they say this happens when the exhaust bracket at the transmission is not adjusted correctly, and one has to make sure the rubber isolation bushings are OK so that there is no direct metal/metal contact between the pipebracket and the trans bracket and be sure there is no distortion or preload when you tighten everything.

Now guess what? I did put some preload on these brackets as the back of the downpipes were too low (lifted them in place with a jack to be able to fix the brackets) and I didn't fit rubber isolation bushings between the pipe brackets and the trans brackets as I assumed the Trans mount would isoltate the whole assy from the cabin anyway. And that's also where I feel the vibration on the trans tunnel.

I think I should start by taking the pipe brackets off and drive around like that and see if there is any improvement. But if that's the problem I don't see why this would happen only in fifth as on the mentioned websites they say it would happen in all gears.
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  #21  
Old 12-20-2011, 11:02 AM
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If you think it is exhaust then you could put in another muffler - generally speaking for (human) audible resonances they will be a function of the length of the exhaust and / or the distances between each muffler. Put in another muffler and you'll shorten the distances - "pushing" the resonances to higher frequencies... I can do some calculations on this if needed but I can't regurgitate anything before the end of this year.
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  #22  
Old 12-20-2011, 07:39 PM
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Quote:
Originally Posted by GGR View Post
Thanks all for your input.

Cth350: my 4th is 1:1 and 5th is .875. Noise is not affected by turns or lane changes. The car was on a dyno last Saturday (see my other post in the “outlaws” thread), it’s a shame we didn’t think of tracing the noise. I was not the one operating the car and the guy stayed in 4th. But I’m sure the noise would have been there in 5th at 80mph.

Sjefke: Yes, engine power causes changes in volume but not frequency, but only in 5th and at 80mph. I’ve tried to determine if something in the trans could cause that, but I don’t really see. All bearings are in motion in all gears. If it was a main shaft bearing the noise would be there each time the engine reaches 3000 rpm, in any gear. If it was a secondary shaft bearing the noise would be there at 80mph whatever gear. The only elements that could cause the noise are the 5th gear pinions, but that doesn’t resemble a gear noise? Wouldn’t the noise be there all the time, like a whine with amplitude variations related to rpm while in 5th? I will move my hand along the tunnel and feel whether I sense changes in vibration moving back and forth over the tunnel. But I already noticed I can feel a vibration in the back of the trans tunnel on the passenger side. It’s right behind the flex disc (which is new, genuine MB, big size like on the 560s). I will need to see if that vibration increases when I’m in 5th at 80 mph, and compare with other places on the tunnel.

Tram: a “resonance noise that sounded like repeated notes on a bass organ at certain speeds and RPMs under load”. Yes, this could be a good definition of what’s happening. But if it were related to crankshaft bearings, I guess it would also make the noise under load in 4th, which is not the case.

Mercmad: my rear diff is a 3.27. In 5th it’s equivalent to a 2.85, like on a 6.3. Originally that engine was coupled with a 2.72 rear end, and some 5.0 were even fitted with a 2.24 on some W126s. So I don’t think my rear end ratio is a problem here.

I think Sjefke is putting us on the right track: “if your noise (frequency) is there either way, but worse going uphill and less downhill, then the volume (amplitude) is proportionally to strain/power”. What could cause a frequency to be there in all cases, with an amplitude proportional to strain/power, only in 5th at 3000 rpm and 80mph?

I know engines develop some resonance noise at 3000 rpm. When I was a kid, I’ve seen old school mechanics checking time advance at 3000 rpm just by the sound of the engine, like woom woom woom. This is very easy to do on L6s, but I guess other engines do the same. The noise I’m having in the car is exactly that resonance noise engines do at 3000 rpm, and it is indeed happening at 3000 rpm. But why only in 5th?

Thanks all again for the help.
Just a note to what you wrote above: The VW noise would only show up at a certain steady highway speed in 4th- usually around 60- 70 MPH depending on the individual case... no other gears, and no other speeds. It seemed to have to do with the exact type of load under very precise circumstances. In other words, a couple MPH more or less would eliminate it. This in no way meant immediate catastrophic death for the engine, but it was damned annoying.
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1968 230S Automatic, Elfenbein
1975 O309D Executive Westfalia Camper Bus, Blau/ Weiss
1972 280SEL 4,5 Dunkelrot
1966 VW Type 34 "Grosser" Karmann-Ghia
1963 VW 1500 Variant Pearlweiss
1969 VW Variant Automatic, Perugruen
1971 VW Squareback Automatic, Clementine Orange
2001 E320 4Matic Wagon- Our belated welcome to the 21st century! Polar White
1973 280SEL 4,5 Sliding Roof "The Bomb", Dunkelblau.
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  #23  
Old 12-21-2011, 11:08 AM
GGR GGR is offline
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So, I took those brackets that were holding the downpipes to the trans out yesterday evening and took a drive on the highway. Things are MUCH improved. The car is much quieter in general, much less vibrations transmiitted into the cabin.

The woom woom noise is still there but much less, at 75mph and is not related to engine load anymore. in fact it's even a bit noisier when coasting, but all in all it is now very bearable. I think that direct link to the exhaust was having the latter amplify the noise with more or less amplitude depending on engine load.

Given the overall lower level of noise, I now noticed that woom noise at around 1500 rpm in fifth. I think it is more of a prop shaft or rear axle noise, it is not depending on engine rev.

5th is also a bit noisier than other gears, but not that much.

I will check engine/trans/prop-shaft/rear axle alignment next time the car is on a lift. I may also declare it normal, keeping in mind that the car is now bare of any sound proofing. I think things will be much improved when I work on that. I need to find the right compromise between damping sound and adding weight. But it's another chapter.
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  #24  
Old 12-21-2011, 01:24 PM
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What model W111 do you have? Out of curiosity, why didn't you use a stock exhaust instead of configurations from a R107 and W109? I also wanted to add that worn or broken sub frame mounts can resonate a lot of noise into the interior (and vibration).
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  #25  
Old 12-21-2011, 01:57 PM
GGR GGR is offline
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Quote:
Originally Posted by JPMOSE View Post
What model W111 do you have? Out of curiosity, why didn't you use a stock exhaust instead of configurations from a R107 and W109? I also wanted to add that worn or broken sub frame mounts can resonate a lot of noise into the interior (and vibration).
That's a a good question. It's a '62 W111 Coupe fitted with a euro 5.0 M117 out of a 450SLC 5.0 and a 5 speed manual transmission.
I used the r107 tri-y system manifolds and downpipes and then a W109 6.3 exhaust line for its pipe diameters. More here: http://www.peachparts.com/shopforum/vintage-mercedes/300989-my-62-mercedes-220se-coupe-5-0-videos.html

Front subframe mounts are new.
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  #26  
Old 12-21-2011, 04:37 PM
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Very cool! I love the color of the car as well!

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1970 280SE 3.5 Cabrio
1987 560SL
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