Sound Proofing a 126 - PeachParts Mercedes-Benz Forum

#1 05-26-2007, 01:17 PM

I have been looking for a way to make the interior of my 83 300SD just a bit quieter at speeds in the 80 mph range since I spend a considerable amount of time traveling at those speeds

. I have searched plenty before attempting this project but almost all searches ended up with no real information or half baked attempts due to lack of time, finance or both. Hopefully this post will answer a few questions for anyone wanting to attempt a similar project. The following is a list of what I have done so far.
Removed seats, carpet, console, rear shelf, all factory sound proofing that was loose and falling apart.
Installed butyl mats from secondskin audio http://www.secondskinaudio.com/ (damplifier pro) everywhere it was humanly possible to reach. "painted" over mats with a visco elastic ceramic impregnated vibration and sound proofing coating, also from 2nd skin (firewall). Removed factory hood pad and "painted" underside of hood with "firewall" coating, reinstalled pad.
This was a 3 day project and was very effective at almost eliminating all road noise but unfortanately has done almost nothing to control engine noise at these speeds.

It did however almost eliminate engine noise at 2000 rpm and below.
I have ordered a thick aluminized fiber based pad that is used called "the insulator" from Harold electric http://www.heco.net/noise.html. This stuff is used to quiet the noise from diesel buses and motor homes. I am planning in installing on the exterior of the firewall from the top of the firewall where it meets the hood down to and along the trans tunnel and attaching it via self tapping screws with fender washers. I have much higher hopes for this pad and will post results after completed.
I will post pics of entire project soon.

Kuhlrover · #2 05-26-2007, 01:48 PM

Your approach with the hood and firewall insulation would be the next step. Look at the fire wall and make sure there aren't any small holes and make sure the grommets completely seal around the wires and vacuum tubes that go through the firewall. Use a little RTV or putty to seal these if you see holes.

Check your motor mounts and trannmission mount is to make sure they are healthy. This will prevent the vibration of the engine from being transmitted from the engine to the body.

The last and most drastic step is add a belly pan under the engine and insulate it with the same stuff you used on the hood. The belly pan prevents the sound that comes off the engine from being reflected off the road surface and back into the car. I know this works because I drove around for a while with my wifes 2000 VW Beetle TDI without reattaching the pan. It makes a difference. Of course your car wasn't designed to have a belly pan. What shape, where will it attach, will the engine properly cool are all questions that will need to be engineered for.

Oh, one other thing I just thought of, I have seen insulated blankets for engines and turbos. That route my be worth some research.

TimK

#3 05-26-2007, 01:48 PM

More pics of sound proofing project

#4 05-26-2007, 01:51 PM

Just for an FYI. All engine and trans mounts are new. I also "painted" the whole undercarriage and in all wheelwells also.

#5 05-26-2007, 01:56 PM

here is the hood and undercarriage.

I will post pics of the insulator pad after installed.

sixto · #6 05-26-2007, 06:45 PM

How much heavier is your car now?

Sixto
93 300SD 3.0

dieseldan44 · #7 05-26-2007, 06:53 PM

Your road noise intrusion is very likely from an open hole somewhere in the firewall. A single 'direct path' can ruin a lot of well thought out soundproofing.

Nice job so far...Id like to do the same thing someday to my 123...

Austin85 · #8 05-26-2007, 11:52 PM

The best way I found over the years to deal with road noise is to get 4 really good aftermarket speakers........

and turn the music up real loud.!!!

...

#9 05-27-2007, 10:59 AM

The whole project so far has added roughly 60 lbs to the car......I am not too worried about it going any slower

and yes bigger speakers help as the pics will prove but after 8 plus hours on the road that is a bit much to deal with.
Thanks for all who added "check for holes". I have a few small ones that will be sealed.

vstech · #10 05-27-2007, 11:07 AM

how Much $$ on this project?
I noticed you did not remove the center console and completely cover the trans tunnel. while this would certainly push the job out of the 3 day completion time frame, I bet a ton of noise could easily be transmitted from there.
John

#11 05-27-2007, 12:31 PM

The console was removed completely out of the car.....I just did not take any pics during that phase

. The only place I did not apply the mat and paint was under the heater/AC assembly. I installed as far as I could get under. I did however remove the duct system that travels along the tunell and attaches to the AC housing via snap clamps. (once again no pics of this)

I have roughly $700 into the whole project....not including time

#12 06-11-2007, 11:13 AM

Just in case anyone is interested...here is the final update on the sound proofing job.
Installed the "insulator" pad along firewall using a combination of glue and self tapping screws, sealed all holes (wires, throttle, hoses, etc) penetrating firewall, installed 2 layers of Jute padding (purchased from Lowes in the flooring department, $42 for 100 sq/ft) over top of the 2nd skin products on floorboards, rear floor under seat and inner firewall.

Total cost for the whole job was roughly $800. Being that I routinely drive 1,000 miles per week this was not a bad investment.

Final verdict...........road noise has been almost eliminated, engine noise below 3,000 rpm has been reduced drastically, above 3,000 rpm it has been cut roughly in half.

If anyone would like any further details or info on what I used or how I did it please feel free to PM and ask.

arminski · #13 06-22-2007, 10:58 AM

Great advice! How much insulator did you use at the firewall and how much benefit do you estimate that gave? I am thinking of ordering and doing the firewall portion of your project!

probear · #14 06-22-2007, 11:21 AM

My biggest gripe with noise in my SDL is the wind noise from the door pillar. I've check the door seals, and conditioned them, but there still seems to be that wind noise. Unfortunately, since I'm tall, my seat is back and my head is right nest to the pillar.

Anyone have any suggestions to help with this?

vstech · #15 06-22-2007, 11:24 AM

Quote:

Originally Posted by probear

My biggest gripe with noise in my SDL is the wind noise from the door pillar. I've check the door seals, and conditioned them, but there still seems to be that wind noise. Unfortunately, since I'm tall, my seat is back and my head is right nest to the pillar.

Anyone have any suggestions to help with this?

this type of noise is usually caused by the huge gap between the door and the body of the car, getting some balloon style rubber and attaching it to the door to fill this gap, should remove that noise.