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#1
12-18-2013, 10:33 PM
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Shaky idle - w108
When I am stopped at a stoplight the whole car shakes a little, enough for me to feel it while sitting in the driver's seat.
The engine mounts looked ok last winter, and I don't remember about the subframe mounts. What should I look on either? I don't think either are horrible bad/falling apart, or anything like that. But obviously some/all are transmitting too many vibrations. What brands are recommended? I know to stay away from URO. Thanks,
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Csaba 1972 280SEL 4.5, silver 
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#2
12-19-2013, 08:53 AM
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If any of the mounts you metioned are original, they should be replaced.There are also a couple of vibration dampers (they look like "mini" shock absorbers) attached to the engine and the frame that are probaly "perished". Then there is the question of whether or not all ignition/ fuel injection components are up to specifications in all (and there are many) respects. Are the trigger points free of oil? Is the fuel pressure regulator properly adjusted? Are the fuel injectors clean and producing a got spray pattern? Ignition wires/plugs/points reasonably new and properly adjusted? Are there any vacuum leaks? Ignition timing correct?
Even when all these things are up to snuff, it's difficult to get these V8's to idle PERFECTLY.
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Berfinroy in CT Present vehicles: 1973 300 SEL 4.5 1959 Rolls Royce Silver Cloud I 1959 Ford Thunderbird convertible/430 Past vehicles; 1958 Bentley S 1 1976 ex-Max Hoffman 6.9 1970 300SEL 2.8 1958 Jaguar MK IX 1961 Jaguar MK IX 1963 Jaguar E-type factory special roadster 1948 Plymouth woody 1955 Morgan plus 4 1966 Shelby GT350H Mustang
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#3
12-19-2013, 12:43 PM
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i had a similar issue on my w211, but once it warmed up the shaking went away. turned out that the plugs needed to be changed and was causing that shake at idle.
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W211 '03 E320 | W108 '72 280SEL 4.5 http://i66.photobucket.com/albums/h2...ps9b542eaa.jpg http://i66.photobucket.com/albums/h2...ps5723c50f.jpg
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#4
12-19-2013, 10:50 PM
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The engine was rebuilt this spring and I went through everything ignition/FI related, but I will double check the idle mixture. I am pretty sure the 'mini shocks' are there to absorb engine torque reaction at high power settings, so I don't think they'd cause a vibration issue.
I'm pretty sure the subframe mounts are original, so it looks like I have a project for next year. Thanks,
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Csaba 1972 280SEL 4.5, silver
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#5
12-20-2013, 07:33 AM
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I worked on an early 450SL that had the same problem. It turned out to be rock hard motor mounts.
If you leave the car in gear at idle, open the hood, and listen carefully, you should be able to tell if the shaking is coming from a rough idle. Of course, be sure to secure the car so it won't move.
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Chuck Taylor Falls Church VA '66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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#6
12-20-2013, 08:55 PM
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Csaba
I suspect that it's a missing cylinder. Maybe a clogged or poorly connected injector or weak spark.
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With best regards Al Last edited by alabbasi; 12-20-2013 at 10:18 PM.
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#8
12-20-2013, 10:19 PM
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Maybe the electrical connections to the injectors. Those D-Jet connectors do not clamp on as well as the L Jet and later connectors.
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With best regards Al
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#9
12-21-2013, 11:44 AM
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I agree with the other two who said spark plugs, I had this very issue 3-weeks ago on my W111 and one spark plug was fouled and not firing. I should say that any of the proposed issues could be your, but this is cheapest and easiest to check and remedy first.
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1962 220SE W111 Coupe, 2nd owner http://img.photobucket.com/albums/v3.../SideSmall.jpg The Coupe Group (W111/112 coupes and cabs) official website The Coupe Group on Facebook MotoArigato: Roadworthy News & Humor
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#10
12-22-2013, 08:58 AM
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These engine are very heavy and the have a lot of torque. Consequently they are very hard on motor mounts. They get compressed and lose their ability to isolate engine vibration. This gets worse when you are stopped in gear.
You can tell is the engine is missing by putting your hand on it or simply listening to the exhaust while it's idling in gear.
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Chuck Taylor Falls Church VA '66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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