TECH TIP Technical Index

Interior Upgrades Ė Tech Article #1

by Mike C. -

Sound Deadening

I donít know about you, but I am particularly bad about going overboard in the projects that I do. I particularly like to see how I can get the car built with some of the up-to-date techniques that the new car manufacturers use. These techniques include fit and finish, engine and drive-train power and smoothness, and the NVH thing you read about in Car and Driver magazines (noise, vibration, and harshness). I like the challenge of taking an old VW and making it rival some of the new cars of today in terms of NVH. There are a lot of VW owners want to keep the charm and magic of the different kinds of noises created by the air-cooled Beetles, Busses, and Ghias. However, there are some who may want to step up to the challenge of being able to hold a nice, quiet conversation in their old VW while going 65 mph down the interstate. In this article, Iíll show you how to turn your VW into a Lincoln in terms of applying sound deadening techniques.

Iím going to assume here that you are already in the process of restoring your VW or you are at least redoing the interior anyhow.

  1. Everything needs to be completely stripped out of the passenger compartment, including the seats, headliner, and carpet. Make sure that any old insulation padding is not left on the roof or any side panels inside the car. Also strip all the tar boards off the floor pans and make sure the pans and other sheet metal are as clean and free of dirt and oil as you can practically get them. If you had to put in new floor pans or you refinished your old ones to like-new condition, then your job will be much easier.
  2. Remove the engine so you can have full access to the firewall.
  3. Take off the old insulation from the engine compartment and clean all the sheet metal thoroughly.

For the job, you will need:

  • 5 rolls of Ĺ" jute padding that has an aluminum facing on one side
  • 10 rolls of asphalt-based sound deadening sheets
  • 2cans of 3M high-temperature spray adhesive
  • Pair of heavy duty scissors
  • Box cutter
  • Heat gun or hair dryer.

The jute padding will be used in between sheets of the asphalt-based material. All of this sound deadening can be purchased through J.C. Whitney for a pretty reasonable price. Both types of material come in 48" x 72" rolls. Use the heat gun for softening the asphalt sheets so the sheets will easily conform to the irregularities in the sheet metal stampings, especially in the floor pans. I realize this is a lot of material, and you can do this project in steps as time and money permit. Once you start laying the rolls, you will find out how quickly they get used up.

  1. Start with the firewall. This is where 75% of the noise comes from. If you keep the old insulation handy, you can use it as a template to make the new insulation. Otherwise, cut the insulation to fit the area of interest. The asphalt sheets are adhesive-backed, so you will not need the spray adhesive to stick them on the sheet metal. If the piece of asphalt sheet that you cut is too big to handle without tearing or wrinkling, cut it in half.
  2. Lightly stick it on the firewall. Get out the heat gun and heat up the sheet, pressing it into the corrugated sheet metal, and make it conform to the shape. The better you can make it conform, the better the insulation will perform. Keeping the flat expanses of sheet metal from vibrating is the key to good sound deadening.
  3. After you have the firewall covered with the asphalt sheet, you are ready for the jute padding. Cut a piece to completely cover the firewall the same way as you did the asphalt sheet.
  4. Spray some glue on the asphalt sheet you just stuck to the firewall and stick the jute padding to it, doing your best to make it conform like you did the asphalt sheet, except donít use the heat gun here.
  5. Now cut one more piece of the asphalt sheet, again, the same shape as the firewall pieces, and stick it to the jute padding on top.
  6. Do all the same as above, where the firewall sheetmetal breaks and goes horizontal under the car, except only use a layer of asphalt sheet on the sheet metal and a layer of jute padding. Donít sandwich the jute padding here.
  7. If you want to get really trick, you can get one of those stainless steel firewall covers to finish it off and help reflect heat away from the passenger compartment. Now you are through outside.

  8. Go inside the car and do the firewall on this side. As in the engine compartment, make a sandwich of asphalt sheet, jute padding, then asphalt sheet. Do this on both the vertical and horizontal surfaces of the luggage compartment floor and firewall.

Once you get the firewall completely covered in this manner, hardly any heat or noise will come through here. The difference will be nothing short of dramatic. If you keep your valves adjusted regularly and the distributor drive is not worn (see Bill Conkelís solution Ė excellent article), you will hardly hear the engine run compared to before.

Since this is obviously going to take more space than the newsletter will allow, I will need to do this article in two parts. Besides, itís time to get a bratwurst hot dog after all that work!

Your VW Maniac and tech specialist,

Mike C.