[O'Man]

I am replacing the firewall insulation mat that is on the passengers side of the firewall. I found a "hole" that does not have a gromet / plug.

To give you a reference as to the location of the hole let me give you some information. Looking from the passengers compartment thru toward the engine there is a lage hole with a rubber gromet in it. That hole must be 2 inchs in diameter. I believe that gromet is for the speedo cable to pass thru. The car has an electronic speedo so I am assuming that the 2 inch gromet is fo the cable that is no longer needed.

Looking at that speedo cable hole from inside the car and thinking of it as a clock face there is a SQUARE hole in the firewall that is located on the upper side of the clock face...say around the 10 or11 oclock position. The hole is nicely cut so I think it is original but I have no idea what it does or what is supposed to be in there.

Clearly I don't want to leave this open...heat and nosie can get thru there even when the insulation blanket is on the firewall.

Does anyone have a picture of a clean firewall and / or does anyone know what the heck that square hole is for? If there is some odd ball gromet that goes in there I can order it but right now I have no idea what to look for / ask for / order.

 

[shadowgray396]

Look at this post and see if the hole is on it. Look at #9 in it.

http://www.chevelles.com/forums/showthread.php?t=287239&highlight=Firewall+holes

 

[Bryan59EC]

I'm thinking the fusebox bulkhead disconnect.

Square hole to the left & down of the master cylinder? (from inside the car)

 

[O'Man]

I'm thinking the fusebox bulkhead disconnect.

Square hole to the left & down of the master cylinder? (from inside the car)

No no I did not say anything about the master cylinder. This hole is located at the 11 oclock position as you look at the hole the speedo cable goes thru. This is looking from the inside of the car toward the engine. Being at the 11 oclock position relative to the speedo hole places it above and to the left of that speedo hole not below and to the left.

I did say this "That hole must be 2 inchs in diameter. The 2 inch hole is the speedo gromet hole. At least I believe that gromet is for the speedo cable to pass thru. Not a good job on my part as far as giving directions I guess. The speedo hole is 2 inches ...I measured the gromet that goes in it after my post.

The hole I am talking about is small...3/4 x 3/4 possibly even 1/2 x 1/2 and it is adjacent to the speedo gromet hole.. Might be that someone cut it out but it is nicely cut and by no means a hack job. I think it is factory because it is square. I cannot see somene cutting a nice square hole in a difficult position like that hole is in. I would think ya would just drill a hole and be done with it if ya needed another hole for something.

If you look at the firewall mentioned in a referenced post the speedo hole is way down below where the hole the steering column goes thru. The hole I am talking about would be at the 1 OClock position relative to that speedo hole when you look at the firewall from the engine side. The speedo hole is not labeled in the referenced post. Also the firewall pictured is a 1970...the car I am working on is a 72. While I cannot be sure I think they were adding all sorts of junk between 1970 and 1972 and I assume the 1972 f-wall would have more holes. I don't have any way of knowing for sure that a 1970 firewall is the same as a 1972 firwall assuming each car in question had the same options installed.