w108 Interior Sound Proofing
 

w108 Interior Noise at freeway speed is pretty loud. Now I know I can't sound proof the car but I know there are modern products that restorers and rodders use to hush the interior of an old car.

Has anyone out there tried to hush the noise in the cabin of your old benz?

I regularly drive freeway speeds upwards of 70mph. I know these aren't modern benzes.

I did notice that on the later w108s they took effort to hush the noise coming from the floor pans. there is quite a thick amount of moulded acoustic foam under the carpets.

My question is, is the noise coming from the drive train tunnel? i have a feeling that has weak sound insulation. I'm also guessing the firewall?

My front hood doesn't have a hood pad. Does that really make a huge difference in noise entering the cabin?

Any help is greatly appreciated. thanks!

Hi Nick,

I can tell you what I did but there is a catch to it though, I had no idea how loud it was before I did this.
During the resto of my 108 I stripped the interior down to bare metal, no seats...no carpet, nothing. I even scraped out all the old nasty "sound proofing" along the floor.
From there I painted the entire area with Rust Bullet then laid Dynamat EVERYWHERE from under the dash to up the rear seat back and the hat shelf. I went as far to put in on the roof, doors, A&C pillars and trunk.
After that I put 1/4 thick Dynamat sound proofing foam on the floors, front and back.

I probably over did it but whatever. Its pretty nice and quiet going down the freeway.
I have yet to do new door seals so I assume after I do that it will be that much better.

http://i67.photobucket.com/albums/h2...ps3ep4i8xi.jpg

http://i67.photobucket.com/albums/h2...psiy543h1v.jpg

http://i67.photobucket.com/albums/h2...pscikupqzm.jpg

WOW. Very impressive. I'm more than sure that the results from your efforts paid off.

I've been doing research on sound proofing a car. I found some good info on Welcome to Sound Deadener Showdown | Sound Deadener Showdown

Basically this guy got obsessed with his sound proofing research and posted his results. I think I'm going to take the route of placing smaller pieces of dynamat in key resonant areas and then block the noise with acoustic MLV vinyl.

I'm probably going to do the doors and ceiling insulation last.

You mentioned doing the door seals. I went ahead an replaced my seals when i got my car painted. I got oem, shipped from a supplier in germany. It was the best value i can find on the web. don't expect drastic wind noise reduction. i still hear a good amount of wind noise, but at least the seals keeps the wet out. i'm tempted to put an extra aftermarket seal along the door jamb but i imagine the purists will poop their pants if i did that.

I'll keep you posted on what i decide to do.
2 questions for you

Do you have a front hood pad to dampen engine noise?
How high up the firewall did you go? did you go behind the dashboard?

[QUOTE=n10;3490263]Hi Nick,

I can tell you what I did but there is a catch to it though, I had no idea how loud it was before I did this.
During the resto of my 108 I stripped the interior down to bare metal, no seats...no carpet, nothing. I even scraped out all the old nasty "sound proofing" along the floor.
From there I painted the entire area with Rust Bullet then laid Dynamat EVERYWHERE from under the dash to up the rear seat back and the hat shelf. I went as far to put in on the roof, doors, A&C pillars and trunk.
After that I put 1/4 thick Dynamat sound proofing foam on the floors, front and back.

I probably over did it but whatever. Its pretty nice and quiet going down the freeway.
I have yet to do new door seals so I assume after I do that it will be that much better.

Thanks, It was a total pain to do! Next time I wont go that crazy :)

Lots of good info on that website...talk about dedication!

I don't have a hood pad. I looked into an aftermarket option but was concerned about the amount of heat and the ability of the adhesive to keep it there. Though it would probably make a good dent in noise.

With the firewall, I went up as high as I could reach without cutting my arms on the underside. I recall it all the way up to the wiper motor.

Gotcha. ya. i imagine engine noise is making its way through the fresh air cowl and directly into the cabin. so i imagine putting a hood pad helps. if mercedes put a factory foam hood paid, i'm sure they did it for a reason.

I'll probably put a modern hood pad that's meant specifically for heat and sound dampening.

My 1987 300D turbo is silent compared to my 280se. So i get irritated every time i switch back to driving my 280 on the freeway. It's not that relaxing.

btw. this is where i got my door seals. MB Classics

Haha!

n10, notice any difference in terms of heat transferred to cabin with the Dynamat in place?

Well being in Seattle it doesn't get too hot but the last few days have been rough for our standards. :o
Parked...In the driveway at home on "hot" days its warm inside but not like you would expect. I park underground at work so theres no time for it to bake all day

Driving...I do still get some heat from the engine bay on the freeway so I gotta hike up my pants from time to time

I suggest trying Don's system: Welcome to Sound Deadener Showdown | Sound Deadener Showdown I did (partially, still work in progress).

The resonance panels are identical to the high-end cars, and a roll of MLV is not too bad price wise. I've driven in cars with the Dynomatt vs. the little I did, and his system works.

On mine the windnoise from the vent window is the loudest. It makes a buffeting sound. Is this common?

With my vent windows, I pulled the door panel and tightened up the linkage one turn. This pressed the window deeper into the old, compressed window seal and eliminated some noise. Worth a shot - lube the mechanism while you're in there.

I did the same thing, as n10, to my 68 280 se coupe last year. I also put dynamite inside the doors and behind the front kick panels (inside the fenders). At the same time I replaced the all of the carpet and the floor pads. The interior looks great the outside noise has been reduced. Most importantly my 300 watt Kenwood with front and back 6 inch speakers and 8 inch sub-woofer sound amazing. The work was well worth it.

My Approach
 

I've been doing a ton of research on other drivers experiences and methods using sound deadening. I want to take a cost effective approach but splurge on some of the obvious areas such as under the hood and around the drive train tunnel and firewall.

I'm going to start at the biggest source of noise. that 4.5 V8. I bought Dynamat Hoodliner. It's 3/4 thick and I've been reading some really good success stories when it comes to hushing noise. Plus it will be the easiest noise suppressor to install. I'll try to test noise suppression using my iphone DB meter app. Relax, I know it's not super scientific but i'll keep the environmental factors equal to try and A/B test as clean as possible. It's better than no measurement at all.

I will use the leftover material to insulate the transmission tunnel, then layer it with MLV acoustic vinyl. I'll probably sandwich a layer of closed cell foam then put another MLV layer to make sure the tunnel is soundproof. I will do the same + dynamat with the rear hat shelf because i know the trunk is a big noise source.

From my research, from a weight saving and cost savings standpoint, I don't have to completely cover every square inch to metal with dynamat. I can cut it into squares and place it in key areas were the metal resonates. I can see there is some factory deadening so i can supplement around that. I don't have a kickin stereo anyway, so i'm not worried about subwoofer vibrations

Behind the rear seat will use more dynamat over the wheel wells and do the same layering with ccf and MLV. My 300D has 2 layers of 1/2 thick acoustic batting. I got the 2nd layer from another mercedes at a junk yard for super cheap, so i may just pick up more of that stuff since it's easy to get.

I'm going to do 1 major area at a time, and I'll do my best to measure my results with the DB meter so I can share with you if I had success, or just wasted my time. Ultimately what matters is how it sounds to me. I've got a really good ear and I get really annoyed at road noise, so I'll know if my efforts made a difference regardless of what the db meter says.


This guy had an interesting write-up of his sound deadening efforts. Cool Read overall.
Infiniti qx70rs - 1000+ hp luxury hybrid suv project


WISH ME LUCK!!!!

If there are any w108 owners on this forum that live in Los Angeles, i'd love to go for a ride in your car. I've only driven in MY w108 so I have no comparison of how quiet/smooth a w108 should be.