When did Porsche transition from silver cad plating to gold cad plating on 911's?

[edmayo]

Chris, you certainly are a wealth of information

[DynoDave]

Hi Chris,

Just wanted to personally say thank you for all of the information you listed. It is greatly appreciated & very helpful. Here in Colorado, we have a great source for cad plating at a local airport.

Best regards,

Dave

[smedley]

For the LAST time......cadmium plating disappeared with rare exception in the late 50s.

The plating on late 50s 356s and all 900 cars was zinc, repeat zinc!! This has been reinterated by several 356ers and 911 guys who have consulted platers and metallurgists. Lew Morman, long time PCAer, autocrosser and concour guy....AND metallurgist for Champion Sparkplug set me straight on this back in the 70s.....all of the platers since then that I have worked with in Indianapolis, Chicago, and now Sacramento have confirmed this.

The plating used on fasteners is an industry/DIN thing not Porsche.

Later 356s had silver or "clear" zinc. Sometime in the late 60s the industry started using a phosphate wash which coated the zinc yellow/green. We see this transition when Porsche made their supply orders for the 900 cars, and they stated receiving yellow zinc. It is well documented among the 356 crowd that yellow started appearing more on '65 C cars. Conversly, early 900 cars had some left over clear zinc.

The rare exception? Recaro had all of their slider rails and levers done in real silver cadmium. Again, I had professionals in the business verify this. Those of you who have worked on or dismantled cars know that the rails and levers on these early cars show more corrosion and "chalking out" of the plating......which is why the industry went away from cadmium.

[chris_seven]

Mark,

I have to say that I agree, if you look at the finish on AN washers this is a typical Cadmium finish and the appearance is different to chromated Zinc.

It seems to me that Cadmium Plating is much more readily available in the USA than here in the EU but I am not sure what chromating treatments are used.

Chromating is really a surface conversion rather than a coating and its main benefit is that it improves zinc's resistance to 'white rust' by a significant degree.

It can also be used to make the 'break out' torque values needed for free running nuts more predictable.

Again in Europe hexavalent treatments have more or less vanished and been replaced by a trivalent system.

Trivalent solutions are less effective in the prevention of 'white rust' and are often accompanied or have been replaced by an 'organic topcoat' or seal which can be a similar colour to conventional yellow zinc but can be thicker and cause some issues when applied to fasteners.

It is a bit of a minefield so some care is needed.

There is also a tendancy to electroplate a significant number of parts that were never plated in the first instance and we then end up with that 'over-restored' look.

[smedley]

Chris,

Now you're at a molecular level discussing tri and hexa valent conversion coatings!

True cadmium is hard to find in the states as well. When I was restoring a pair of sport seats I had to plead with my platerbto do a cadmium set up and run for rails and levers.

Simple clear and yellow chromate zinc are readily available, although EPA regs has forced platers to use different reagents resulting in a clear zinc finish much more bright with a blue tint than the zinc of even ten years ago.....and certainly brighter than what was originally on 356s.

[Richy]

I am working on a 30,000 mile original '67 911 that still has some clear zinc 6mm bolts for the engine tin .

[chris_seven]

Just back from the platers - this was plated and 'clear' passivated.

I think you can also specify 'blue' as per Cadmium but my plater only has 'Yellow' and 'Clear'



We use another plater with very small barrels with a fine mesh for carb and other small parts.