Insulating of the Dually Crew Cab firewall is fairly straightforward.   First, let’s look at the original Chrysler installed insulation in both trucks…

The `93 D-250's insulation was a pressed rubber/foam composite panel glued and screwed to the cowl and firewall. The glue is green and appeared to have been slathered onto the truck using a paintbrush. There were large gaps and areas where insulation was not tight around holes and parts.

The Dually still had some insulation left over from the OEM in `82. It consisted of pressed felt padding glued to the cowl (no foil), and black paperboard with pink fiberglass over the firewall. The paperboard/fiberglass was held to the firewall with metal tabs folded over.

Another photo of the `82 firewall with insulation.

The goals are as follows:

• Sound Deadening better than the factory version
• Improved thermal insuation for higher overall HVAC system efficiency (the crew cab is a larger volume for the truck to heat and cool)
• Addition of the reflective foil to hold heat in (winter) and keep unwanted heat out.
• Cover as much square area as possible, leaving minimal uncovered firewall/cowl areas around passthroughs, holes and fixtures.

There are only three products required to accomplish the insulating job, and they are items which I recommend to keep on hand:

• JC Whitney Foil Backed Insulation Roll (24ft or 48ft or available in smaller sections)
• 3M brand Super 77 Spray Adhesive (best spray adhesive you will find, like ACME glue in a spray can)
• Aluminum Foil tape (a specialty tape found at Lowe’s or Home Depot, in the tape section or in the duct section.  Not mastic tape)

A photo of the Insulation and Aluminum tape. The insulation is felt-based, not spongy foam (not like house carpet padding). The tape is adhesive but has a paper backing that has to be torn off (it is fairly thin stuff).

3M Super 77 Multipurpose Spray Adhesive

PREP WORK
Remove everything you can from the area to be insulated.  Try and mark (or be aware of) areas you do not want to insulate (example; around firewall holes where wires protrude or around the HVAC unit).

This photo shows the firewall before I cleaned it and had removed everything. I even removed the pedals to prevent any obstructions during the process.

Clean the firewall or floorboards by removing dust, dirt, rust, grease or other foreign materials.

The finished Insulation job.

Mask off the windshield and any other areas where glue would be bad (any spray adhesive is difficult to remove and will require chemicals for cleanup; the oversprayed adhesive will collect dirt if not removed from undesired areas).

Example of insulation around the accelerator pedal cable passthrough. I cut a square around the clip, then used the foil tape to prevent the insulation from coming loose and obstructing acceleration. The blue silicone on the tip of the pedal was used to repair the rubber isolator at the cable end - after 297k miles, it had seen some wear and degredation.

The general instruction here is to pre-cut and fit the insulation, then  spray adhesive on the insulation or firewall.   WATCH YOUR OVERSPRAY!

You can always cut big, attach, then trim back the insulation to the areas where it is needed.  Some difficult to shape contours are best done this way; however, be advised that a very sharp utility knife is needed to cut this stuff.  Multiple slices across the material are required to get pieces to separate, so do as much trimming as you can using sharp scissors or other tools before the insulation is attached.

A photo taken from the passenger side of the cab, showing finished insulation.

After all areas are covered and trimmed as desired, go back and cover the seams, corners and unwanted holes with the foil tape.  The aluminum tape commonly has a matte finish; with light rubbing using a cloth during installation, the tape will polish up to a chrome-like finish, just like the insulation.  It will look like a one-piece job unless you look very carefully for the tape edge lines. (Use a cloth you don’t mind getting dirty, the aluminum foil tape will turn it black).

Because I had carefully trimmed the insulation around the HVAC mounting area, I did not have any issues with insulation being caught between the HVAC box and the firewall.

Future plans (after the truck is running) are to insulate most of the rest of the cab with this material – primarily under the floor and on the back wall, but also potentially on the doors, pillars and even the roof if I really wanted to.  The reflective foil will help immensely with heat control during any season.

Copyright Kris Wickstead ©2009.  Always use good sense, the proper safety procedures, PPE and safe equipment.  Follow all manufacturers instructions.  For informational purposes only.  Not a guarantee of any kind.  Use information at your own risk.