Is it some kind of spray foam?

[C101972]

What does the factory put on the inside of the cab corners? Looks like some kind of spray foam. Thanks Chuck
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[Palf70Step]

Personally I have never seen anything in the cab corners of an original truck. Only time I have seen spray foan is when someone is trying to make a cheap backing for a bondo repair on one.

[C101972]

I have had two trucks’68 & ‘72. 68 had 75000 miles on when I purchased. And 72 was in the low 40000. And they both had the same type of spray foam material in corners?
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[CG]

This is weird, sort of ... I swear I just posted an answer here and when I looked again my post was gone?

Then I see the same question was posted in the builds area ... Ok Im not crazy lol.

[C101972]

I wanted to post it here first but it was in project section yesterday, but had no responses. So decided to give it a try here? Sorry for the confusion.
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[indymachinist]

Pretty sure any foam you are seeing there is rust repair as was stated above.

[C101972]

Like I said that my 72 was low mileage and I was second owner, and didn’t have a spec of rust on it.
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[cj847]

I've had 2 of these trucks and both had something in the corners that looked like globs of dried up seam sealer. It wasn't attached to anything. Both had original corners.
I suppose it could have fallen from above or was part of some type of seal between the cab corner and the rocker?

[68 C10 Driver]

My 68 C10 had the original cab corners when I got it, and the only thing on the inside of the cab corners was the original green paint.

[mikeshome]

Maybe some one has added it for sound purpose.

[special-K]

Got pictures to help us understand what you are seeing? Are you seeing just a blob? Could be excess seam sealer, but would be hard and smooth texture. Nothing like spray foam. I can certainly say GM put no sort of spray foam in the corners. Not a little and not a lot

[AllGoNoShow]

I have it on my truck…just looks like a large glob of seam sealer.
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[Jason Banks]

I've seen what is described. It's not like the modern spray foams. I almost seems like some type of rubbery foam. Definitely not seam sealer. When I have seen it, you could just take your finger and rub it off. It's pretty crumbly.

[Redneck Rydes]

I worked at GM assembly for 30 years,when the guys on the line were applying sealer,some of them would clean out the guns by shooting the sealer in areas nobody would see, cab corners, lower trunk areas by the 1/4 s,so when moisture would get in that would be the first place to rust,so having said that,it was not part of the build process to put sealer in there,actually if you look deep into those areas, there was a small relief to let out comdensation so it would not build up with water

[C101972]

My’72 is in the frame off process, I removed the big globe out of the cab corners. So I don’t have any pictures of what it was, now that being said I wish that I would have taken pictures. I was just wondering if it was supposed to be there. Thanks everyone for all of your responses. Chuck
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[72c20customcamper]

My 72 had a big glob on the passenger side . Dug out 90% of it no rust at all on the corners also found a socket bit buried in the middle of it

[jumpsoffrock]

I believe they simply used the same seam sealer as the rest of the parts of the cab. The application was generous; similar to how they did it on my '71 Camaro throughout the cab and even on my '56 F100 in it's cab corners. All vehicles seam sealers are very fragile, and am sure that is due to 1) their initial composition, and 2) age(obviously). The Fords corners were full of loose chunks, and so is the rotten GMC cab I'm removing for my project.

I have two '72 cabs that appear to be original and I'll take pictures today, since one of my chores today happens to be cleaning out my new cab.

[71CHEVYSHORTBED402]

If you mean rear lower corners and wall, yeah glob of seam sealer of some type as Jumpsoffrock says.