[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.