Description: Fastback Trunk/Backseat Transition Underlayment
Model: Mustang, Shelby, BOSS
Model Options: Fastback (Sportsroof)
Factory: San Jose, Dearborn, Metuchen
Manufacture: Dead Nuts On
Accuracy Rating: 9
Best Repro Available: YES
All fastback (Sportsroof) models came from the factory with this piece of underlayment for sound deadening that covered the back of the trunk and rear of the back seat. It was made of asphalt tar with paper on one side and shiny plastic on the other. It was installed as shown in the pictures with the paper side up (most common) or the plastic side up. We have seen it installed both ways in original survivor cars so either way is correct.
We made our dies from several original surviving examples we have documented over the years including low mileage 22,000 mile BOSS 302. This unusual design is unique to the fastback.
Q: Will your underlayment crack and fall apart like the originals did?
A: No, we used binders in the tar that hold it together so you can put it in and out without it ever breaking apart.
Q: My original underlayment is a lot darker than some of your pictures. What gives?
A: The darkness of the paper varied in our original examples from very light to almost black. Our experience is that slight changes in the tar and the our shops ambient temperature during manufacturing effects the final color. Cooler temps will make the paper lighter and hotter temps will make the paper darker. Take a look a the last picture showing the two extremes in color variances. We shoot for the somewhere in the middle but you could get a piece that is closer to one of the extremes. Good news is all are correct.
Q: My original underlayment seems thicker than your reproduction. Are you making it the correct thickness?
A: Bob Perkins said the same thing when he first got his first piece of underlayment. If you look at an edges of original pieces they are swollen at the edges from years of heat cycles so they look thicker but when you cut down the middle of it you will find ours is the same approximate thickness.
Q: Wow, thats a lot of money for a piece of tar. Why does it cost so much?
A: Yes, we totally agree it's expensive but its not cheap to make. We make it ourselves in California with our own custom production equipment in small runs. The materials are not inexpensive and our partially automated manufacturing process is labor intensive. The size of the die and the equipment to die cut it out is another reason. If we could source the material itself from a mass production manufacture it would be a whole lot less but its just not available.