How to further reduce cabin noise? - PeachParts Mercedes-Benz Forum

goldstone · #1 12-11-2002, 07:39 PM

As is frequently noted on these boards, the cabin of the W126 is very quiet. Nonetheless, it seems to me that my '89 420SEL is noisier inside today than it was years ago (wind & road noise). Is this my imagination? Or are there tricks to improve the car's noise reduction ability? (FYI: I've always used Michelin MXV4's, so I don't think the increased noise is attributable to the tires.) Would replacing/reconditioning the door seals help?

Again, this could all be in my head, but I'd be interested in any suggestions.

PS: You guys are making me dangerous: Besides successfully repairing the long-malfunctioning fuel sender using the sage wisdom I found in this forum, I just changed my transmission fluid/filter/seal for the first time on my own. (I realize these are not "big-deal jobs for many of you; but for me, they are.) I'm enjoying my Benz (202,000 original miles!) more than ever. THANKS!!!

tkd_M119 · #2 12-11-2002, 07:53 PM

Ear plugs?

Maybe ad dyanamat to doors and floors. I know there is already some noise abatement material in there but more does help.

Try quieter tires. I used to use MXV4s and was surprised at how much quieter other makes of tires are. Yokohama dbs are reputed to be extrodinarly quiet. Your gaskets around the doors maybe worn as well. You'll notice this as increased wind noise.

goldstone · #3 12-11-2002, 10:29 PM

Thanks for the ideas, tkd_M119! Your gasket suggestion is useful given my desire to simply restore "as new" condition.

Your other two recommendations--adding "Dynamat" (by the way, what is it and how would one apply/install it were one so inclined?) and/or using different tires--modify the original design and are less appealing to me--though others may want to give these ideas a try.

For the record, as regards tires, I have tried other brands over the years (Continentals and Dunlops, though not Yokohamas) and have returned to the MXV4's. The Michelins simply provide a level of winter handling the others I tried did not.

As for gaskets, can my existing ones be treated/reconditioned, or is replacement the only way to go?

Thanks again for any help or additional suggestions.

Ali Al-Chalabi · #4 12-11-2002, 10:54 PM

Dynamat is a sound insulation material. It is sold on a roll. If you want to go this route, just stick it underneath the carpeting or wherever you want to add more sound insulation. It is a good material, however, it is a bit pricey.

blackmercedes · #5 12-12-2002, 12:07 AM

Dynamat is used by car stereo nuts to damp body resonance and stop the high frequencies from bouncing. Of course, glass is bad for this, but dynamat helps in other areas.

As a side effect it blocks road noise. You'll need to pull up the carpets and lay it down. Fitting the carpets again can be a headache, but MB carpets fit pretty well, and their molding is robust.

Some people also undercoat the car to deaden road noise, but I don't recommend it. Most of that tar stuff will end up trapping in some moisture and you'll get rusty floors down the road somewhere...

haasman · #6 12-12-2002, 01:34 AM

Trying to find out where the noise is coming from is a good idea.

I have a friend who did this by using a piece of garden hose. He held one end to his ear while putting it around doors and window areas while someone drove the car for him.

Additionally, it could be that your door striker plates could use an adjustment so they close tighter against the doorframe. It is actually not too hard to do. You'll need a hex socket that fits into the striker plate. Word to the wise, make sure it is a new socket (actually the hex end) and be sure it is FULLY seated into the hex head bolts. Just a little adjustment goes a real long way.

Another tip, this one from a refrigerator repairman: Put a dollar into the door jam and close the door on it. If you can easily slide the bill out it needs to be adjusted.

Haasman

tkd_M119 · #7 12-12-2002, 01:48 AM

Goldstone, it's most helpful if you start with the inside of the door panels. I used to have a Miata - talk about noise! I noticed a major improvement in NHV reduction and also gained an added bonus of real nice THUNK upon closing the doors. I found that it also helps to have more than just one layer. I don't know where diminishing returns are with this approach though.

I reccomend the door panels because it's the easiest, most noticable place to start. It also help to add dyanmat to the floor panels/firewall, the area under the rear seats and the trunk lid and walls (quite a bit of noise/resonance can come from here. If/when I have more time I'm going to try this with my w124 400e. I have come accustomed to the low NHV of my old Q45 and I find my E to be a bit noisy. Though a bit pricy, I think I'll be using Dyanamt "Super" - its their most HD product and does not require heat for proper adhesion.

If you really are ambitious you can fill your rocker panels and possibly A pillars with structual foam. Don't know if you might run into long term rust problems by blocking water passages. I do know this also helps greatly reduce NHV. My former (now wifes) Q45 has foam in the A pilars and I think some parts of the rockers as well. I read an article in SSC (Sport Compact Car) in which they did this to a late model 300zx, mainly to try an stiffen the structure - the found that there was a major reduction in NHV. The actually used foam that was for a Q45.

keithed · #8 12-12-2002, 12:18 PM

Dynamat is good stuff. But another option is to find a industrial/commercial insulation shop and ask them if they will sell you a couple of sheets of Armstrong (Armoflex rubber insulation). They come in 4' by 8' sheets and thickness of half inch up to one and a half inch. Not only will it dampen the noise, but the insulation of the heat and cold are unmatched in you auto application. The best part it should be cheaper than the dynamat and ask for a pint can (which is more than enough) of Armstrong 520 adhesive. Use cheap throw away brush to apply glue to insulation and surface to be applied to. Only a one to two inch circle in different spots is all thats needed. Dont glue whole thing, not necessary. It bends and twist easily and will lay flat for easy installation.

I have seen whole vans and vehicles insulated with the foam (Ureathane). Its is so comfortable as far as the A/C and heater go but the biggest problem is the noise and squeakin from the movement of the metal. I would never put any of the spray foam in any cracks or creavess because of sound issues, in any of my vehicles.

Just my two cents worth, and working with insulation for 27 years.

Keith

haasman · #9 12-12-2002, 12:58 PM

keithed

what about the spray foam that one can use to fill-in cracks around say a sink? When this stuff drys it seems to be quite firm. Is it your experience that this will generate sqeaks as well?

Does the Armstrong mat you spoke of come any thinner? Great tip.

Haasman

jsmith · #10 12-12-2002, 01:53 PM

i was messing around with this after i put on a "free flow" muffler to try and reduce some low end resonance. i used sound absorbing padding that is used for laminate flooring. i covered the spare tire well and added a layer under the trunk mat and behind the gas tank. i also placed some under the rear seat. i thought i could hear an appreciable difference - not enough for what i wanted though, because i wound up reverting to a stock muffler. the stuff i have is 1/4" of dense rubber material with a fabric backing made from recycled tires. they usually sell this as an "upgrade" to the regular padding that they install.

sixto · #11 12-12-2002, 03:14 PM

Does you car have plastic panels under the engine and transmission? If not, maybe you can 'borrow' a set of encapsulation panels from a 300SDL or 350SD/L. It shouldn't affect engine cooling.

Sixto
91 300SE
87 300SDL
83 300SD

timreid · #12 12-12-2002, 03:49 PM

goldstone
I'm working on the same question of how to reduce noise in my 400E.

It's best to combined a damping material (such as Dynamat) and a sound absorbing material, such as foam with a rubber backing, fiberglass or some still use jute. The damping materials reduces the resonant vibration which reduces the high resonant noises that enters into the car cabin. This is applied normally to metal structure of the car, and helps reduce the transferring vibration (noise) to other structures in your car.

The composite materials or the sound absorption materials are used over the damping materials. I personally selected a damping material with the adhesive backing, and where possible I'm going to use a self-adhesive composite sound absorbing material. One of the most interesting materials I found is a composite consisting of foam with a urethane facing that has lead sandwich between the foam layers.

If you decide to add sound materials, you may want to try to do all sections of your car (trunk, floor doors, etc.). If you do just your floor, you may notice more noise being transmitted from your doors, it sort of like opening a window.
When doing the floors or other areas cut the material in the largest section as you can and tape the seams, you'll want to avoid cracks were sound can enter. I believe most of the noise we are trying to eliminate in our Mercedes is road noise, so I would use some damping material and use more absorbing composite materials.
I notice on my car a lot of this noise comes from the door area, door post, rocker panels (as mentioned, with good corrective suggestions), this is a difficult area to add any sound absorption material to. I'm going to remove a door panel and try various material thickness to see what fits best, if you are going to do your doors, I'll let you how thick of material I used.

All sound materials usually work, the thickness is important for sound and fit, cover all areas possible, tape seams, fill all cracks.
Enjoy the quietness, hard to find today.
timreid

goldstone · #13 12-12-2002, 04:20 PM

GREAT recommendations. Thanks for giving me my next project for the 420SEL.

Cheers!

keithed · #14 12-12-2002, 04:26 PM

hassman

Yes I beleive it does come as thin as a quarter inch in thickness. And you can add to any thickness by gluing multiple layers. It is the tightest cellular rubber on the market that I am aware of. And it can be painted, or sealed etc, but you wouldn't need to in the floors, door panels, trunk etc.

However most of the commercial shops will probably only have half inch or above. But you never know, its worth a shot.

Keith

mhingram · #15 12-12-2002, 04:29 PM

Goldstone,
I use silcon grease for all my rubber seals whenever I do the 15 thousand mile service. Just put some on thumb and forefinger and knead it into the rubber on all the doors and the trunk seal. My ears still feel the door shut so they are sealing well. Also works well with the sunroof rubber.
m