Soundproofing a w108? - PeachParts Mercedes-Benz Forum

TroutMD · #1 11-19-2016, 07:29 PM

Well, everything on my 280SE 4.5 is working perfectly now so I am getting a bit bored

I am thinking of a worthwhile winter project and I thought of soundproofing... Anyone have any experience with this undertaking? What is worth doing and what material to use?

My car has the original hood pad in very good condition save for a grapefruit size hole right in center of hood.

fonzi · #2 11-19-2016, 08:38 PM

It would be interesting to read what everyone thinks are the most intrusive noise makers in a w108. I had mine up to about 90 mph for the first time (and the passenger front was down a little because of the stripped window regulator) and think I heard significant wind noise from the triangle window or maybe the driver door mirror?

If it's the window making noise, I guess it's my seals I should look at.

What kind of sound proofing are you thinking of?
Floor pan metal?
Engine noise?
Drive shaft and differential?
Suspension?

There are a lot of ways to look at sound proofing.

JMela · #3 11-19-2016, 08:55 PM

You could pull out carpet and dynamat the floors before replacing. That would quiet things down.

Idle · #4 11-19-2016, 09:45 PM

Quote:

Originally Posted by JMela

You could pull out carpet and dynamat the floors before replacing. That would quiet things down.

To expand upon this....

Sound is vibration. To limit the sound you must limit the vibration.

When this car was new the hot set-up was undercoating. This has proven to be a great way to trap water under your car and rust out the floors. So if you car is not undercoated then don't even consider it.

Dynamat on the floors, the inside of the door (against the door skin) and in the rear seat bulkhead area will do a great deal to stop vibration and therefore noise. This has to be applied with a wooden roller and is not a slap-dash sort of thing but it really works. Dynamat will have more details on their web-site.

One odd place to apply this stuff is under your doors. Some cars can't take this because there is not enough room to apply it and still let your doors close. But if it fits it will make things tone down. This has to do with where your ears are in relation to the bottom of your doors. The doors vibrate just a bit and the sound is directed right at where your ears are located.

I have tried to go cheap by tearing some insulation out of a 123 or 126, from behind the rear seat. It damps things down a bit but not really enough to notice. This type of stuff acts as a barrier between the vibration of the metal and your ears. Dynamat stops the vibration at the source.

JMela · #5 11-19-2016, 10:45 PM

Quote:

I had mine up to about 90 mph for the first time (and the passenger front was down a little because of the stripped window regulator) and think I heard significant wind noise from the triangle window...

If time and pressure have compressed your wing window seals such that they no longer seal tightly, you can adjust the lever mechanism a bit more tightly and get a better seal.

After pulling the door skin, clean and lube the ball & cup lever mechanism while tightening slightly.

If you've got the $, new seals would be the best option but prices are ridiculous.

TroutMD · #6 11-20-2016, 11:59 AM

OK, thanks everyone. My door seals are good, so I think will try the Dynamat route first. Any advice on what Dynamat product/thickness to get?

Jub · #7 11-20-2016, 03:35 PM

I did this to my floors, doors, kickpanels, and under dash cardboards. It works great! Also replaced door seals with that cheap URO crap (have to slam doors hard everytime...live and learn).

Also, for under hood what I did was go to junk yard and look under random cars for liner that would fit (pulled one from Volvo circa 1990's; cut to fit).

The only place not covered is the metal behind rear seats-between trunk and seats. Never got around to this, although I hear that noise comes from this via rear wheels?

Interestingly enough, the only wind noise I hear comes from the triangle windows (nothing major).

Can't remember what I used, but I bought on ebay (is had silver part with black rubbery part underside with adhesive built in).

Jub

nicknack280 · #8 11-21-2016, 12:50 AM

I had a thread about this topic a while back as well. http://www.peachparts.com/shopforum/vintage-mercedes/369517-w108-interior-sound-proofing.html

Stretch · #9 11-21-2016, 05:41 AM

If you have old or original door seals then the chances are quite high they are a source of noise in the cabin. Try taping the door gaps with masking tape and see if that makes a difference.

(I'm not suggesting you leave the tape there for ever - this is just to test the effectiveness)

nicknack280 · #10 11-21-2016, 07:23 AM

Quote:

Originally Posted by Stretch

If you have old or original door seals then the chances are quite high they are a source of noise in the cabin. Try taping the door gaps with masking tape and see if that makes a difference.

(I'm not suggesting you leave the tape there for ever - this is just to test the effectiveness)

I've put brand new door seals on my w108 4.5. Didn't seem to help much to be honest.

So far the biggest difference that i've seen in reducing noise transmitting into the cabin was changing my motor mounts and sub frame mounts (which were completely obliterated)

nicknack280 · #11 11-21-2016, 07:43 AM

Quote:

Originally Posted by TroutMD

OK, thanks everyone. My door seals are good, so I think will try the Dynamat route first. Any advice on what Dynamat product/thickness to get?

read this before you fork out the dough sound deadening material.
https://www.sounddeadenershowdown.com/

Great writeup on this guy's obsession with perfecting sound deadening.
One thing that stood out(which is also a method that I've seen on multiple sites and youtube videos) is that dynamatting an entire floor pan is not necessary. It's the law of diminishing returns. They all say about 25% coverage of dynamat or other CLD is all that is needed to cut 99% of vibration of the resonance of sheetmetal. Any more than 25% is just added labor, weight, and cost of materials. The real sound blocking comes from the layering of decoupling material and MLV, Mass Loaded Vinyl. MLV is a dense vinyl sheet. When sound waves hits the dense vinyl sheet it turns that energy into heat.

Give it a read. It's pretty interesting. This the method I plan on using when I tackle the same project on my w108.

Here's another project writeup I came across.
http://legacygt.com/forums/showthread.php/mass-loaded-vinyl-soundproofing-very-satisfied-133782.html?

ejboyd5 · #12 11-21-2016, 08:22 AM

My 1972 280 SE 4.5 is quiet as a clam with no need for aftermarket soundproofing. Of course, it has been garage kept for its entire life and has rolled only 58K miles which probably helps to keep the noise at factory levels.

nicknack280 · #13 11-21-2016, 11:44 AM

Quote:

Originally Posted by ejboyd5

My 1972 280 SE 4.5 is quiet as a clam with no need for aftermarket soundproofing. Of course, it has been garage kept for its entire life and has rolled only 58K miles which probably helps to keep the noise at factory levels.

damn i wish you lived in Cali. I'd love to hear what a new 108 sounds from inside the cabin at freeway speeds. i have yet to ride in a vintage mercedes in mint condition at freeway speeds so i don't know what to compare mine to.

ejboyd5 · #14 11-21-2016, 01:47 PM

Think of the sound produced by a mouse urinating on cotton.

TroutMD · #15 11-21-2016, 04:32 PM

Quote:

Originally Posted by ejboyd5

My 1972 280 SE 4.5 is quiet as a clam with no need for aftermarket soundproofing. Of course, it has been garage kept for its entire life and has rolled only 58K miles which probably helps to keep the noise at factory levels.

Huh. .

Mine is also a very low milage garage queen, but I still think it is quite loud comparatively speaking to let's say w126 eight cylinder S-class. I would actually compare it more to 80s model diesel in terms of decibels heard in the cabin.