Types of Plating

[Clark K.]

I have read the archives and much is written about the types of plating on which parts. I have yet to find something about the color/appearance of the plating. I wanted to share what I have found.

I just had my clutch cross shaft ("Z" bar) replated in cadmium. I had the clutch replaced and it just seemed to be a good time to remove the shaft. I did this because at the chapter meet in April, the Flight judging Chassis team deducted one originality point for this shaft. The judge's note was that this bar should NOT be painted. It appeared to them to have been painted. In going through the '65 JG, I discovered that the cross shaft was either zinc or cadmium plated. I was in no position to "argue" with the judges since I did not know cadmium plating from silver paint. Since I live in an area with a multitude of aerospace manufacturer's, the restoration shop I use had a vendor who does cad plating. Voila! It's done.

I always get zinc dichromate (a gold color plating) mixed up with cadmium plating. So, if you are also confused, here is a website link that explains it all: http://429mustangcougarinfo.50megs.com/new_page_26.htm
This webpage even describes the zinc phospate (black) plating on some bolts, etc. Be sure to read the safety warning about cadmium poisoning at the bottom of the web page. -Clark

[Michael F.]

Re: Types of Plating

I am sure that silver cad used in 67 and back, I think the judging books say zinc ok too, I think that is bogus and is a buddy system trade off because some don't want to get it done right and admit that fact. I NEVER saw zinc back in the day, was all cad. I am sure someone will come on and say different and they have that right....to many compromises being made by a few to make it right for their cars in my opinion and some judges support it.

We all owe ncrs a great debt of gradtitude for all they are doing and have done in the past, my only gripe is things becoming the "right way" when they never were that way back in the day. just my 2 cents.

[Donald T.]

Re: Types of Plating

I am sure that silver cad used in 67 and back, I think the judging books say zinc ok too, I think that is bogus and is a buddy system trade off because some don't want to get it done right and admit that fact. I NEVER saw zinc back in the day, was all cad. I am sure someone will come on and say different and they have that right....to many compromises being made by a few to make it right for their cars in my opinion and some judges support it.

We all owe ncrs a great debt of gradtitude for all they are doing and have done in the past, my only gripe is things becoming the "right way" when they never were that way back in the day. just my 2 cents.

Michael,

I have to disagree. I have restored many plated parts that GM specs called for zinc or cad, and I have yet to encounter cad (including cross shaft). Cad may have been used, but it's use was very limited if it was ever used at all. Cad and zinc are virtually indistinguishable so misidentification is common. I know the parts I have restored are zinc because zinc and cad are incompatible. If you attempt to plate zinc over even a trace of residual cad, not only will the plating not work but the solution in the plating tank will be contaminated and will have to be replaced. When I replate parts, I bead blast the parts and clean them in an ultrasonic cleaner. I never remove all of the original plating in the blast cabinet because there is no benefit. Every single Corvette part I have ever replated has been compatible with the zinc, therefore the original plating is zinc.

I personally believe restoring parts with cad is irresponsible. Cad is nasty stuff and can cause cancer among other things. Keep in mind when you cad plate a part, there may be some poor sole down the line that will toss the part in a blast cabinet and inhale a very dangerous material. Cad is not original and whatever perceived benefits do not outweigh the potential health risks. Just my opinion.

[Gene M.]

Re: Types of Plating

Donald,
You are correct. I would also add that zinc plating is most common on original parts as a sacrificial plating. In conjunction with a zinc plating many plating houses add a clear chromate if requested. This makes the "silver" coloring more shiny. I do not know if this additional chromate was spec'd on original prints. But it does help aid in protection against elements. Age and weathering tone down the sheen.

A dichromate is available in yellow (gold) and black. The black dichromate is a good substitute for black oxide or black phosphate. But it has much more sheen to it. As it ages it is less distinguished from oxide or phosphate.