Underbody Mounting Plate Finishes for AOS Bodies

[Bob P.]

I have read through several post in the archives and haven't found a consistant opinion on the underbody mounting plates for 1966 AO Smith bodies. I doing a frame off resotoration and need help with identfying the finish or color of: inner and outer seat belt anchors, splash shield brackets, seat mounting plates - inside and out, front seat mount bracket. If I've missed a part please let me know and help identify the finish or color. Thanks for your help!

[Gene M.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Bob,
I think you will find the 4 seat belt braces are a very poor quality plated finish. It is so poor I can't tell if they are zinc, cad, or phosphate. Rear (4) seat mount thick plates were natural. Front seat brace and splash plate toe brackets were green zinc chromate paint. Shifter lower brace above tunnel insulation is also green zinc chromate paint. I think the firewall body mounts were green zinc chromate paint too but can't say for sure. Gas tank vertical hat section is green zinc chromate paint. Rear body mounts get black out from wheel well treatment. The entire bird cage as you know is also green zinc chromate paint. Rear valance nut plates are also green zinc chromate paint. I'm sure I left something out on the AO Smith body riveted pieces.

[Matt L.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

hi Bob,
i hope this pic helps you some. this is from my very original low milage 66. you can see some finishes and others have some patina. but this is the best i could get it cleaned.

take care,
matt
DSCF4887.jpg

[Bob P.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Thanks Matt, I forgot that you basically have the same car as mine. Picture is good enough. I have one question though. Would you say the splash plate toe brackets were green zinc chromate or black or natural. In your picture it looks like they are black. Any signs of green?

[Matt L.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

hi Bob,
i thought your name looked familar. you are more than welcome to come take a closer look at the car. here is a different shot. they look black to me in this pic. i would have to go look again with my own eyes to feel 100% comfortable though. i will keep digging for pics or if you need a specific one,let me know.

take care,
matt
DSCF4889.jpg

Thanks Matt, I forgot that you basically have the same car as mine. Picture is good enough. I have one question though. Would you say the splash plate toe brackets were green zinc chromate or black or natural. In your picture it looks like they are black. Any signs of green?

[Russ S.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Bob,
I think you will find the 4 seat belt braces are a very poor quality plated finish. It is so poor I can't tell if they are zinc, cad, or phosphate. Rear (4) seat mount thick plates were natural. Front seat brace and splash plate toe brackets were green zinc chromate paint. Shifter lower brace above tunnel insulation is also green zinc chromate paint. I think the firewall body mounts were green zinc chromate paint too but can't say for sure. Gas tank vertical hat section is green zinc chromate paint. Rear body mounts get black out from wheel well treatment. The entire bird cage as you know is also green zinc chromate paint. Rear valance nut plates are also green zinc chromate paint. I'm sure I left something out on the AO Smith body riveted pieces.

I am working on a very original A O Smith body that had undercoating on the vertical bracket just forward of the gas tank and it is black under the coating.


I should expand on this a bit so I don't mislead someone into thinking they had undercoating on theses brackets as a rule. It only had a small amount at the very top of the bracket. I wouldn't think that it got there from the factory but I don't know. The underside didn't have more than the normal amount that the factory put on.

[Gary B.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

I am working on a very original A O Smith body that had undercoating on the vertical bracket just forward of the gas tank and it is black under the coating.

Russ,

Can you clarify what you mean by the "vertical bracket just forward of the gas tank"? Do you have a photo or is there an item # you can refer to in the AIM?

Thanks,

Gary

[Scott S.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Russ,

Can you clarify what you mean by the "vertical bracket just forward of the gas tank"? Do you have a photo or is there an item # you can refer to in the AIM?

Thanks,

Gary

Gary,

I believe Russ is referring to the underbody reinforcement located in your 1966 AIM on UPC 1 Boltweld-B1, Item 10, "Reinforcement U/Body", GM 3850114.

It is the same part number from 1964-1967, and located on the same page (1Boltweld-B1) for 1964-1967, either Item 9 or Item 10, depending on the year.

[Russ S.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Russ,

Can you clarify what you mean by the "vertical bracket just forward of the gas tank"? Do you have a photo or is there an item # you can refer to in the AIM?

Thanks,

Gary

It is the 3-1/2 X 11-1/2 inch bracket riveted to the rear side of the luggage area back wall in the center of the car. You can see it thru the gas door hole if there is no gas door boot in place.

[Jim D.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

I am working on a very original A O Smith body that had undercoating on the vertical bracket just forward of the gas tank and it is black under the coating.

The one on my 65 A O Smith body is black as well, no undercoating. I posted a pic. in this thread - https://www.forums.ncrs.org/showthre...t-Mount-Plates

[Gary B.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Russ & Scott,

Thanks. I know which bracket you're talking about.

As an aside, there is a 2006 article by John Hinckley in the Corvette Enthusiast that has the best photo (attached) I know of that shows the underbody of a St. Louis car. In that photo the largish, seat belt reinforcement plates that wrap around the corners of the floor pan clearly look to be painted black. In fact, at least the inboard small rectangular, rear seat track reinforcement plates also look to be black. Most people think that all four of those small rear seat plates were natural, but that's not what John's photo suggests to me.

That same article has an image of an AO Smith underbody, but that image is cropped to show the shifter reinforcement bracket, the inboard ends of the long, front seat reinforcement brackets, each of which are clearly zinc chromate. It also shows one the pointy tunnel insulation clips, which is clearly black.

Gary

Corvette Enthusiast June 2006.png

[Scott S.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Russ & Scott,

Thanks. I know which bracket you're talking about.

As an aside, there is a 2006 article by John Hinckley in the Corvette Enthusiast that has the best photo (attached) I know of that shows the underbody of a St. Louis car. In that photo the largish, seat belt reinforcement plates that wrap around the corners of the floor pan clearly look to be painted black. In fact, at least the inboard small rectangular, rear seat track reinforcement plates also look to be black. Most people think that all four of those small rear seat plates were natural, but that's not what John's photo suggests to me.

That same article has an image of an AO Smith underbody, but that image is cropped to show the shifter reinforcement bracket, the inboard ends of the long, front seat reinforcement brackets, each of which are clearly zinc chromate. It also shows one the pointy tunnel insulation clips, which is clearly black.

Gary

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Gary,

I have wondered about that photo each time I see it. That is either an exceptionally well-preserved underbody, or the photo is of a restoration in progress. The green zinc-chromate on the rocker panel brackets and what appears to be black paint on the seat belt reinforcement brackets (and rear seat attachment plates) looks aaawwfully nice to be original. Also, if you blow the photo up 500-800% there appears to be some white overspray on the green zinc-chromate along the inboard side of the rocker panel brackets and on the outboard end of the black front seat reinforcement, I'm not sure why.

For the rear seat attachment plates, every example in Adams' book showing the undercarriages (one each model year) sure do look like plain or natural steel, as do other original GM factory photos (larger and better quality than the photos in Adams). In the three large black & white photo examples I've seen, two 1963s and one 1964, the outboard seat-belt reinforcements appear to be silver-zinc (or Cad). The outboard rear seat attachment plates are darker than the seat-belt reinforcements, but much lighter than the black frame paint right next to them.

About the transmission tunnel insulation clip, if you blow the photo up 500-800% (assuming your photo is from the pdf version of the article, which it appears to be), it looks like the black clip (if it really is black and it's not a trick of the lighting) is a replacement part. The points appear to have never been bent, unlike the original clip directly across from it, which is well-worn with both points bent outward.

[Gary B.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Scott,

I had always assumed that that image was part of John's photo archives documenting some aspect of the original GM process, but you raise some good points. Maybe John will chime in and give us some more info about the origins of that photo and the car in question.

Gary

[Bill H.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Gary,


For the rear seat attachment plates, every example in Adams' book showing the undercarriages (one each model year) sure do look like plain or natural steel, as do other original GM factory photos (larger and better quality than the photos in Adams). In the three large black & white photo examples I've seen, two 1963s and one 1964, the outboard seat-belt reinforcements appear to be silver-zinc (or Cad). The outboard rear seat attachment plates are darker than the seat-belt reinforcements, but much lighter than the black frame paint right next to them.
.

I'm headed to the garage right now to finish glassbeading the rocker channels on my 67 AOS. I think that the r/a seatbelt mounts are a crappy zinc plate, the rear seat reinforcement plates may have been natural (mine may be too rusted to tell). But they are definately not black.
The front, long reinforcements are definately black. The shifter boot reinforcement was zinc chromate.
If I can get a good pic as I take the rust off the seatbelt plates, I'll post it.

[John H.]

Re: Underbody Mounting Plate Finishes for AOS Bodies

Scott,

I had always assumed that that image was part of John's photo archives documenting some aspect of the original GM process, but you raise some good points. Maybe John will chime in and give us some more info about the origins of that photo and the car in question.

Gary

Gary -

I don't recall offhand exactly where I got that photo, but I've noted several finish inconsistencies in A.O. Smith underbody brackets/reinforcements over the years; I'd summarize them as follows:

Shifter opening reinforcement - have never seen anything but zinc chromate.

Seat front reinforcement channels - have only seen one pair that were black primer - all the rest were zinc chromate.

Seat track rear reinforcements (4) - natural (unpainted).

Seat belt anchor reinforcements - marginal quality zinc plated.

Rear bulkhead vertical reinforcement channel - have seen both zinc chromate and black primer.

A.O. Smith had no black primer paint system, so the black reinforcements noted must have been painted by the supplier and furnished to A.O. Smith painted.

I have no clue why the rear seat reinforcements (4) are consistently natural (unpainted).

These are just observations over the years - I never documented build dates to establish any patterns.