[Shiny]

Curiosity post, ignore freely...

Did GM or Pontiac change plating specs between 1970 and 71?


I have a dented rear bumper, coded 8A25, consistent with it being original to my car, coded 09C.

I have a nice "near NOS" bumper I bought years ago, maybe from someone here... it is straight, coded 2B22J. It is NOT a 70 bumper...is 71 or 72.

When I set them side by side, I noticed a difference in the plating.

The 70 looks darker, like more nickel. The other looks brighter, like more chrome.

I think both are Pontiac parts, not repro, but I could be wrong if repros are date stamped. The 71/72 is more pitted. The 70 has held up better overall.

When I searched online, my AI buddy said GM changed plating specs.

Is this true?

Here's the internet legend as I received it:

🔍 What Changed in GM Bumper Plating

1970 bumpers

Typically had a heavier copper/nickel undercoat beneath the chrome.

This produced a warmer, slightly “deeper” chrome tone and better resistance to pitting.

Suppliers were still using plating standards developed in the late 1960s, before cost-cutting pressures.

1971–72 bumpers

GM began shifting contracts to different suppliers, especially as production volumes increased.

Nickel undercoats were often reduced in thickness, with more reliance on chrome flash for shine.

Result: brighter appearance out of the box, but more prone to corrosion in harsh climates.

Some plants also experimented with different polishing processes, which altered reflectivity.

Regulatory backdrop

The early 1970s saw new federal crash and corrosion standards. GM was preparing for the 1973 “5‑mph bumper” rule, which drove changes in bumper design and plating.

Cost and environmental pressures (EPA plating bath regulations) also nudged GM toward thinner, faster plating cycles.

[Held for Ransom]

So, your 8A25 bumper had no G (or other letter) at the end?
Interesting on the plating style differences.

[Shiny]

No letter, which I understand was a location or supplier code.



Car was built in Pontiac.

Any insight into the plating difference?

[Shiny]

I just finished cleaning up the newer bumper I've been saving.

It had these stickers on it. Does this mean it was a replacement part from the counter and not from a factory-assembled car?





The plating on it is definitely not as robust as what's on my original.

[TXSTARFIRE]

I would say that is a service part. Looks like a shipping label in the 1st picture?

[bluejudge]

Originally Posted by Shiny

I just finished cleaning up the newer bumper I've been saving.

It had these stickers on it. Does this mean it was a replacement part from the counter and not from a factory-assembled car?





The plating on it is definitely not as robust as what's on my original.

Hi Shiny, I sent you a PM

[turbo69bird]

I have been told by many that service parts that were chromed were not as nice of a finish as the factory installed parts. Door handle are one example they gave. This was from someone who worked for Pontiac. But I really have no comparison other than some new inbox NOS parts I’ve seen that definitely were not that well chromed. That’s not a definitive answer I know but thought it may be helpful in some way.

[Shiny]

Originally Posted by TXSTARFIRE

I would say that is a service part. Looks like a shipping label in the 1st picture?

Thanks, that's also what I assumed. Any way to know when it was actually built?

Originally Posted by bluejudge

Hi Shiny, I sent you a PM

Replied, thanks

Originally Posted by turbo69bird

I have been told by many that service parts that were chromed were not as nice of a finish as the factory installed parts. Door handle are one example they gave. This was from someone who worked for Pontiac. But I really have no comparison other than some new inbox NOS parts I’ve seen that definitely were not that well chromed. That’s not a definitive answer I know but thought it may be helpful in some way.

Thanks. This might make more sense than a significant change in plating quality for factory builds between 70 and 71.

But I'm still curious about the plating differences and why it happened... Is it a location/supplier thing or was it an actual cost- or regulatory-driven change in plating spec?

Would be cool to see the prints and engineering specs for these old parts!

Mike

[bluejudge]

I attached the sticker that I have on my NOS bumper.

[Shiny]

Thanks for posting the sticker.

Mine has the same PN 484946 but the stickers are different, suggesting they came from a different manufacturer or were made at different times:



As I understand, the 70 bumper is unique, with the 71 and 72 adding notches for bumper guards or something similar.

The one on my car does not have notches and no stickers. I believe it to be original to the car, but that's just a guess:



The new one with the sticker has notches (and a different plating). So PN 484946 must have been a "universal" replacement for 70-72 even if different from an original 70, correct?

[bluejudge]

My NOS bumper has the notches too.

Originally Posted by Shiny

Thanks for posting the sticker.

Mine has the same PN 484946 but the stickers are different, suggesting they came from a different manufacturer or were made at different times:



As I understand, the 70 bumper is unique, with the 71 and 72 adding notches for bumper guards or something similar.

The one on my car does not have notches and no stickers. I believe it to be original to the car, but that's just a guess:



The new one with the sticker has notches (and a different plating). So PN 484946 must have been a "universal" replacement for 70-72 even if different from an original 70, correct?