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1972 280se 4.5 w108 and 1984 280sel w126 euro
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41 Posts
Discussion Starter #1
Hello W123 forum. I have a m110 engine in my w126 1984. I have a kind of harmonic low level oscillating hum that I hear from the engine when I go over 65 miles per hour. I feel the vibration oscillation on the gas pedal so I think it's the engine. Has anyone experienced this? Also my transmission has me at 3500 rpms when at 65mph. Is that ok for the engine? And lastly. I want to change the plugs, wires, distributor cap and rotor myself. Any suggestions where to buy this stuff and how to get these items for the engine that I have.

Thanks for your help.


Dan
 

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'73 450SL, '83 300CD, '01 E320 4matic
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2,446 Posts
autohausaz dot com is a good place to look for parts.

As for your noise/vibration issue... The first thing to check is that it is in fact the engine. These cars (especially the 126) is well known for some quirks in the suspension and/or chassis. An out of balance prop shaft for example could cause the problem, or a flex disk, center bearing etc.

Check your wheel bearings also. They will certainly cause a low frequency hum/rumble if they're loose.

If it does turn out to be the engine that is the source of the noise, check the exhaust mounting- the rubber 'donuts' that attach the exhaust can fail. It may also be touching the body some place. Remember that at speed the vehicle twists, and at 3000+ RPMs the engine itself can be slightly 'moved' from where it sits at an idle. There should be good clearance around everything.

The engine and transmission mounts should also be inspected, they are well known to deteriorate. Replacing them is fairly simple.

I'm not sure if the M110 engine has a crankshaft balancer with an isolated rubber pulley or not, but I imagine it does, so you may want to check that as well.

A low frequency oscillation at high speeds is unlikely to be the engine, as it's rotating pretty quickly up there, so any engine related vibration would likely be a high frequency, and harmonics thereof.

I would definitely suggest inspecting rubber mounts (really anything made of rubber at this stage) and the condition of the driveline and exhaust.
 

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Registered
1972 280se 4.5 w108 and 1984 280sel w126 euro
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41 Posts
Discussion Starter #3
Thank you so much for your information Aaron. I am thinking engine since when I take some pressure off the gas pedal the hum changes or if I increase the gas pedal it kind of goes away/changes as well. Taking my foot off completely at 65mph makes the sound go completely away. So I ruled out wheel bearings. I am going to check out the rubber mounts next.


Dan
 

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1980 280ce
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135 Posts
Also, I agree with Akimball442. I really don't think it's the engine if it's a low frequency noise. Since it responds to the gas pedal it would be something in the path affected by the throttle. That would be: transmission, driveshaft, rear end, cv joints, and rear wheels. All spin at a much lower rpm than the engine which could cause the low freq. noise.

And of course check the motor and transmission mounts. If they're broken or worn out the engine/tranny can move around a little which may have something to do with it.

Maybe drive with your windows down and see if you can hear where it's coming from.
 

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1980 280e
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670 Posts
Not sure why people are so gung ho about autohausaz.com, a cap at autohausaz for the m110 is basically $50+s/h they are about $15+s/h on ebay (make sure you know what your part # is they have different versions)

autohausaz.com =http://www.autohausaz.com/search/product.aspx?sid=45awsdinwilvslbh2acmxk55&[email protected]&[email protected]&year=1980&[email protected] Parts&[email protected] Cap
ebay = http://shop.ebay.com/i.html?_nkw=m110+cap&_sacat=0&_odkw=m110+rotor&_osacat=0&_trksid=p3286.c0.m270.l1313

edit: It looks like only one or two caps are $15+$10 s/h, the rest are $12+$30 s/h from china, if you can handle non-bosch parts then I guess there is a savings, but if you insist on bosch parts then autohaus is about as cheap as anyone else it looks like, good deals show up on ebay every now and then thou, I got my bosch cap+rotor brand new for $25 from a person not business on ebay. Basically there are deals out there if you have patience, people don't have to spend astronomical amounts on their benz if they don't want too.
 
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