Monday, April 2, 2012

Firewall and Floor 1

With the dash panel and doors painted I could now focus on the interior details.  I want to install the dash components before I install the engine compartment parts like the brake master cylinder and the headlight and charging system harness because they basically rely upon the dash wiring harness, the pedal bracket, and some other under-dash support items.  So, in the cascading list of tasks that encompass the sequential assembly of a 68 Mustang, there lies the basic starting point of the humble firewall insulation pad.  This shouldn't be a big deal right?  It's just an ugly hunk of rubber coated jute padding.  They must be cheap and plentiful considering the simplicity of their makeup right?  Well, not quite.  A search of the various Mustang forums will net you hundreds of "These repro pads SUCK!" posts.  Evidently, even the most expensive molded reproductions are not quite up the task of being firewall pads.  They are either too smooth, not molded right, or basically just cut wrong requiring modification.  So, I chose to just forgo the drama and refurbish my original pad.  Sure, it's dirty, ugly, broken, and cracked but I learned from flying balsa model airplanes all those many years ago that if you keep all of the pieces, it can be made to fly again with enough patience... and glue.

So, I went out and gathered it up from the shed, laid it out on a plastic sheet and washed the rubber surface with soap and water.  This thoroughly soaked the padding requiring me to carefully turn it over and let the pad dry out for about 3 days.  After it had dried I laid it out rubber-side-up on a makeshift table, and set to work.  I first tried to use super glue to tack the splits together in preparation for a better glue but found that the rubber material absorbed it.  So, I moved on to 2-part epoxy.  This actually worked pretty well but it's application was tedious and the working time was pretty short.  Finally, I chose a product that was designed for binding rubber to rubber called "Shoo Goo" that sets up reasonably fast.  I've used this stuff for years and just happened to have a half tube of it in a drawer so I gave it a shot and it's like it was designed to repair firewall pads.  I had to strategically place blocks and such under the pad at various locations during the bonding of the various cracks to hold the crack closed until the Shoo Goo set up which really only takes about 20 minutes.  I also found that Shoo Goo fills missing sections of the original rubber and doesn't absorb into the padding so that's just icing on the cake so to speak.  I made sure to spread the glue along the crack after filling it to level it out so it would not be noticeable during the next phase which involved rubbing the newly repaired surface down with wax and grease remover and spraying it with very thin coats of 3M rubberized undercoating.  From the trials of others who have restored their firewall pads, it had become evident to me that coating the pad directly with a thick coat of undercoating would actually soften and attack the original rubber causing a poorly textured end result.   I believe this to be caused by the solvents in the undercoating sprays that keep the rubber compound in suspension to be sprayed and thus the first thing the solvents in theses sprays want to do is dissolve and suspend the original rubber coating of the pad itself.  So, this can be alleviated by spraying a LOT of very thin coats from about 1 - 2 feet above the pad until enough new rubber has been laid down to protect the original coating from the solvents.  Not to be completely negative, I also believe that these solvents help bind the new undercoating rubber to the original rubber if sprayed  sparingly.

In the beginning...

On the operating table.

All glued back together.

The first thin coats of undercoating.

Heavier coats, nearing completion


A close-up of the texture after restoration.
So, the firewall pad is ready to go back into the car but how the heck was it fastened there?  I had a couple of pictures from way back when I'd started disassembling and it looked like there were just 2 or 3 sheet metal screws through quarter-sized fender washers holding the pad on in addition to the washer pump, fuse box, and such.  I have no idea if this is how the car originally came from the factory but I decided to get the allegedly original-style firewall pins for 68 from CJ Pony Parts during one of their 20% off sales which was unfortunately out of stock so I moved on to other tasks.  One such task actually needs to be done before the firewall pad is installed and is not exactly concours.

I had done much research on modern sound deadener technology.  There's a LOT of data and threads out there regarding the various products and techniques.  Okay okay, I'll link you a couple like this VMF thread, this other VMF thread, and oh yeah, yet another VMF thread.  Then there are the comparisons of the many stick on and spreadable/sprayable coatings in the Sound Deadener Showdown web site (which also sells their own products).  Personally, I chose a product called RAAMmat due to price and specification.  Also, it has a very good reputation for not being asphalt-based and for remaining stuck on vertical surfaces even in extreme heat whereas other, cheaper alternatives (FatMat, eDead) are reported to drop off of roofs (if you do that) and the inside of doors and quarters during high heat.  Others have reported this to not be a problem if you prepare the surface correctly but I had read a high enough ratio of failure to success for those products so I chose to avoid them even though I am a cheap  b*****d by nature.

So, I ordered a 37 sq ft pack and received it within a week.  Just for your info, it takes about 80-120 sq. ft. to cover every square inch of an entire Mustang from firewall to tail panel (more for roof) in true "OverHaulin'" fashion but that was not my intent.  My intent is to use it sparingly everywhere except on the firewall where I wanted not only the acoustic properties but the insulation properties as well (in addition to the factory insulation).  The rest of the floor will be covered about 25% or less.  Just enough to dampen the harmonic resonance of a large, unsupported section of sheet metal (like the firewall for instance).  The box came with 20 sheets of an aluminum foil, butyl, wax paper sandwich material.  I used my metal sheers to cut it but a box knife would work.  I first placed a strip of masking paper over the area I wanted to cover and drew out a pattern on it.  Then I cut the pattern out and transferred it to the mat and cut out the mat with my sheers.  I was trying to use as much of each sheet with as little waste as possible rather than trying to make it pretty since it will be covered by dash pad and carpet.  After I cut it out, I pulled the wax paper off and stuck it to the firewall and then used a rubber roller to press it on.  I was surprised how sticky this stuff becomes on contact but I found it pretty easy to work with an not messy at all regardless.  I worked this way all the way across the firewall leaving the pedal bracket/steering column area bare as I didn't want to affect clearances.  The end result ain't pretty but I think it will help improve the cabin heat and noise.  I'll post a Part 2 when I finish up the floor toward the end of the restoration.

A box-o-RAAMmat.

Firewall before

Masking paper pattern layed out on a sheet.

After cut-out.

Pressed onto the firewall.

Holes cut out with a hobby scalpel.

Finished passenger side.

Finished driver side. Ready for the firewall pad.
The final thing I needed to do in preparation for heat shield and sound deadener was to install the floor plugs.  I first painted them with a coating of Rustoleum Stainless Steel and enamel clear coat.  Then I used NAPA black firm seam sealer (caulk gun variety) and squeezed out a bead around each hole.  The first hole was a learning experience of where to lay the bead and how much to lay down so it's not as pretty as the rest but after that one, the rest were better and more consistent.  The key was to lay about a 3/16" bead right around the ridge where the hole slopes down and then carefully lay the plug straight down (dome UP) while aligning the screw holes.  The sheet metal screws were then driven through the floor.

First attempt.  A little sloppy.

First attempt plug.  Slipped it back and forth a little.

Consecutive attempts.

Consecutive plugs.

View from below.

Plugged floor.
That's all I wanted to do in the passenger area before I get my firewall pad pins so I moved on to other tasks.


  1. Nice work on the original firewall pad! Another useful technique to put in the file for future reference. Mine was in shards and beyond recovery. So I'll end up getting one of those "suck" aftermarket pads. After you put the sound deadener on the firewall, will your pad go over the top of it? Keep the pix and info coming. I need all the help I can gather for my car's reassembly.

    1. Thanks Dennis. Yes, the firewall pad is going over the new sound deadener.

  2. That is an awesome series of techniques for firewall pad restoration. I have never seen that combo of products used that way but the results look fantastic! I am a HUGE Shoe Goo fan and have been for years! You're a man after my own heart Alex! Drive on!

    1. Thanks Sven! Yeah, the Shoo Goo bonded to the rubberized coating of the pad like it was made for just that purpose. I'm going to rename it "Mustang Firewall Insulation Pad Goo". Yeah, it's a long name but I'm confident that it will catch on eventually. :-P

  3. Amazing work! Shoe Goo as the icing on the cake! I'm totally blown away with your skills since you started this project 68 / Rusty.

  4. Man, I thought I had a far enough head start on you guys that I could at least coast through the summer but Alex just showed up in the rear view mirror - a la Steve McQueen in Bullitt. Keep the pressure on us Alex!!!


    1. LOL! Dude.. this thing is on the road this summer if I have to push it around my cul-de-sac. :-)