Firewall Openings Sealant

[Christopher R.]

I'm looking to better seal the passenger compartment on my '62 from the engine compartment. The AIM shows that p/n 3686628 "compound" was used on the grommets in the firewall where wires and other things passed through.

1. What is 3686628 compound? It doesn't seem to be adhesive cement. The AIM calls out 3695016 for that. I don't want to duplicate it. I want to know if Chevy was using a gasket sealer type goop like Permatex or "dum-dum" type stuff.

2. Whatever this stuff was, did it go on from the front (engine compartment, where it'd be easy to apply.)? Or, the back (passenger compartment, under the dash, where you'd need a midget contortionist to apply it.).

[John H.]

Re: Firewall Openings Sealant

I'm looking to better seal the passenger compartment on my '62 from the engine compartment. The AIM shows that p/n 3686628 "compound" was used on the grommets in the firewall where wires and other things passed through.

1. What is 3686628 compound? It doesn't seem to be adhesive cement. The AIM calls out 3695016 for that. I don't want to duplicate it. I want to know if Chevy was using a gasket sealer type goop like Permatex or "dum-dum" type stuff.

2. Whatever this stuff was, did it go on from the front (engine compartment, where it'd be easy to apply.)? Or, the back (passenger compartment, under the dash, where you'd need a midget contortionist to apply it.).

Chris -

I don't remember the specific chemistry, but the stuff was a black liquid sealer, applied on the engine compartment side; the same stuff was used on midyears on the line and as a water-test leak repair fix.

[Terry M.]

Re: Firewall Openings Sealant

Something like that was used on C3s also to seal the grommets in the dash panel. It is one of my standard deductions on "restored" Corvettes. No one likes that mess.

[Floyd B.]

Re: Firewall Openings Sealant

I've found a good replacement. I have been told that it is an asphalt goop so I just go to the nearest home improvement supply store and buy a can of roof patch cement - the black asphalt tar type. Mix it in a cup with mineral spirits or kerosene until it is a runny, goopy, messy consistency, then slop it on with a tung depressor and 1" paint brush. Use it to seal off all locations that have compromised the firewall (grommets, screws, plugs, etc.). Don't forget the wiper well below the windshield. My '73 had a thick layer of it covering the entire wiper mounts (i.e. not just the screws). I have also been told that it was meant to prevent intrusion of fumes into the cabin.

It looks like the factory orginal goop - to me anyhow.

[Stewart A.]

Re: Firewall Openings Sealant

Could you use Sika's black polyurethane. It's good with heat, seals and sticks to everything ? Stewy

[Barry H.]

Re: Firewall Openings Sealant

Chris, I usually pick up a couple of tubes of cheap asphalt roofing cement at hardware store, easy to apply with standard caulking gun. Easy clean-up with kerosene, seals well, & gets harder over time. Also looks very close to what GM used. I also use it to seal wiring grommets in firewall, & plugs that hold the firewall insulation on the inside. It is great for sealing against water if you plan to drive your baby. Barry Holmes