Underbody Tunnel Insulator

[Jim F.]

I am restoring a 1966, built in December of 1965. The tunnel insulator I removed had been installed with yellow 3M adhesive and was much longer (from close to the firewall and further rearward) than the replacement ones I find. Supposedly the replacement shorty's are as the original ones.
Does anyone have any information on what is correct regarding the tunnel insulation?

[Gene M.]

Re: Underbody Tunnel Insulator

Repro C2 insulation was same size as original in my case. The attachment was sheet metal aluminum riveted to underbody with pointed prongs bent over after pierced thru the insulation.

[Jim D.]

Re: Underbody Tunnel Insulator

GM used cement (3 oz. per the A.I.M.) as well as the bent over prongs to retain the insulator.

[Jim F.]

Re: Underbody Tunnel Insulator

Thanks for the reply. Gene -- Was the original insulator on your car also attached with adhesive?

[Joe R.]

Re: Underbody Tunnel Insulator

Jim,

All the C-2's I have ever restored have had thin sheet metal (steel) retainers with two prongs that pierce thru the insulator and are bent back to secure the insulator in place. Also, some type of yellow contact cement was used to adhere the insulator to the fiberglass belly pan.

JR

[Richard M.]

Re: Underbody Tunnel Insulator

Also..... just for further informatio. St Louis applied the adhesive when the floor pan was upside down. So you may see some drips and sags pointing towards the sky with the car in normal "face down" position.

Before removal. Note some of the tabs are bent opposite of AIM instructions. I believe it to be original as the body was never removed from the frame until I did.
P8100015.jpgP8100016.jpgP8100017.jpgP8100018.jpgP8100019.jpg

Reproduction. Recently installed on the above '67.
P8100012.jpgP8100013.jpgP8100014.jpgP9070061.jpg
P9070062.jpgP9070063.jpgP9070064.jpg

[Michael A.]

[Richard G.]

Re: Underbody Tunnel Insulator

Some pictures of a NOS insulator. Wish I would have taken measurements.

[Joe R.]

Re: Underbody Tunnel Insulator

NOS refers to NEW OLD STOCK!

Was that not removed from a production vehicle?

NEW???????

[Richard G.]

Re: Underbody Tunnel Insulator

It was purchased from GM in the late 70's or early 80's
The blue tag with the GM part number fell off right before the pictures were taken.

It admit it does look like it may have been installed.
If it was I didn't know about it. I doesn't have any holes from the retaining steel tabs.
You can see the GM part number spray painted on it.

Posting the pictures "for what is is worth".
Obviously a GM part. May be a good comparison to judge the aftermarket replacements.
I haven't seen any that even came close to the original design.

Unsure why GM would paint it partially black.
However the GM exhaust system I purchased new in 1978 had black paint on the mufflers.
Similar to the mitted undercoating the car had installed when new.
Seems like an extra step that would have been omitted in all but the one ones used in the assembly process. Go figure.
Rick

[David L.]

Re: Underbody Tunnel Insulator

Rick,

I also have a NOS Insulator, GM # 3912670, that I purchased from my local Chevrolet dealer back in the very early 1980's. I agree with you with the looks of it, much like yours. It has been stored in a box in my garage attic since I bought it. The original part number for the 64-67 insulator was 3834984 as shown in my 1966 AIM and my vintage Chevrolet parts catalogs. GM # 3834984 was replaced by GM # 3912670 in Jan. 1971 as per Chevrolet Parts History for service parts. I'm not sure what the difference is between the 3834984 insulator and the 3912670 insulator but I really do not care as I can not stand fiberglass insulation of any kind even just look at it. I would like to get rid of it as I will never use it. As I remember the 1963 did not have an insulator so why do I need one on my 1966.

Dave

[Michael L.]

[Richard G.]

Re: Underbody Tunnel Insulator

The JM states starting on the first of December 1962 the 63 Corvette used the insulator.
My car was built on the 21 of December and it had the insulator factory installed.

[Richard M.]

Re: Underbody Tunnel Insulator

Mike, Sorry for the late reply as I've been away from 'easy' internet access for about a month......

Here is a link to a post that may help and some photos of the original I replaced on a '67. I seem to recall there was glue on the sides only. As far as a air gap goes, that insulation is not a highly accurate part so it seems that it would be difficult to ensure that a gap between the body exists.

https://www.forums.ncrs.org/showthre...ion#post751402

Also, while searching for my own post, I found another below. Note "glue drip direction".
https://www.forums.ncrs.org/showthre...ion#post753675

Also a '66 I restored and some photos of the insulation area and appears glue on only the sides....
https://www.forums.ncrs.org/showthre...ion#post781025

Rich

[Michael A.]