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jyl jyl is offline
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Questions On Cad Plating Spring Plates

Coupla questions. I'm preparing my spring plates to be plated before installing polybronze bearings.

1. How well do you have to clean up spring plates before taking them to be cadmium plated? Here's some pictures, I've degreased and wire-brushed them but there's still bits of paint etc in crevices. Do they have to be "spotless" or does their prep strip all that stuff off?

2. What should I specify for cad plating that will look like stock? I don't know if mine (pictured) have the stock plating and actually the are slightly different colours. I've seen some cad plated spring plates in prior threads that looked quite "yellow" and some that looked "shiny gold".


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Old 08-13-2003, 09:02 PM
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John

Our spring plates where originally Cad plated. Unfortunately, Cadmium is a toxic substance and the cost of plating with it has gone up dramatically due to disposal costs. Basically, nobody does cad anymore.

The modern alternative is yellow zinc dichromate. It does not look identical to cad but is a reasonable substitute. It also doesn't protect as well as cad, but it is affordable.

This is the same type of zinc plating that is commonly used on bolts, however most bolts have "clear" zinc which gives a silver color.

You need to get all the paint off. They will do an acid bath but it won't clean off paint. It will clean off light oil (not heavy grease) and surface rust.
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Old 08-13-2003, 11:01 PM
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Having just recently done this, while in the process of installing some of Elephant Racing's excellent bronze bearings (thanks Chuck!), I found that a wire wheel on a drill cleaned up the spring plates very nicely (with minimal effort). Here in NC, I was able to locate an established shop that still did the 'gold cadmium plating' (the shop was 'grandfathered in'...). However, my new 930 cross drilled rotors were to big & heavy for their 'cad tumbler', so those were plated with the yellow zinc dichromate that Chuck mentioned. I can't detect much visible difference between the two processes. I'll post some pictures later when I get home...
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Old 08-14-2003, 06:55 AM
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Chuck said it all. I used Yellow Dichromate when doing an engine-out refresh. I'm very happy with the results.
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Old 08-14-2003, 08:27 AM
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A wire wheel in my 4" grinder did wonders to clean up the plates. That is, until in a zealous effort to remove a bushing using my recirprocating saw, I managed to cut a 1/16" groove in one of the plates. Junk.

But at least I have the process down. These are going in for cad plating shortly. Gotta make them look nice to go along with Chuck's stuff.
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Old 08-14-2003, 08:42 AM
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OK, so I want "gold" cad plating or alternatively yellow zinc dichromate. Thanks.

Also, I've read that the spring plates need to be heat-treated or something like that after plating because they get brittle. True?
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Old 08-14-2003, 09:05 AM
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Yes. It's called hydrogen embrittlement. Your plater should be able to handle (arrange) the heat treat for you.
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Old 08-14-2003, 09:09 AM
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Over here - cadium plating was banned about 5 - 10 years ago - I believe it was found to be cancerious! Bright zinc plating is the way to go.
Old 08-14-2003, 09:11 AM
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Chuck, I specifically asked my 'plater' about any weakening of the metal, etc. (as I 'thought' I had read that somewhere before). He indicated that wasn't the case (and I rightly/wrongly believed him) so I haven't had anything 'treated' afterwards...do I have something to be concerned about (...now that I've pratically got her back 'together')?
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Old 08-14-2003, 09:21 AM
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Keith,

I don't know if hydrogen embrittlement applies to CAD.
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Old 08-14-2003, 09:29 AM
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Hmm...what about the rotors? Anyone else have knowledge about "post-cadmium" treatment being "required"? Thanks again...
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Old 08-14-2003, 09:33 AM
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Chuck said..."I don't know if hydrogen embrittlement applies to CAD."

Yes...it will. It depends on the type of steel. Generally the higher ultimate tensile strength the steel is heat treated to, the less resistance to hydrogen embrittlement do to cad plating the steel has. Proper heat treat will manage hydrogen embrittlement potential. Hydrogen embrittlement can also happen on steels exposed to high heat when cad plating starts bubbling. You are probably not working with steels in this strength range (over 200ksi). Wouldn't worry about it.
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Old 08-14-2003, 09:55 AM
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Then, there's powder coating...
Old 08-14-2003, 10:37 AM
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Rob,
Did you get your plates re-done? If so, who did you use?
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Old 08-14-2003, 11:29 AM
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Chris - I had the plates blasted and powder coated - but I also had all the fasteners and torsion bar end covers zinc plated - I was working down in Lowestoft and a local plated did them me - as much as I could carry for 25 including acid diping to clean them up.
I am planning to post some photos soon of the on going resto - the whole back end is dropped and engine/gearbox bay re-painted - saving up just now for trailing arm bushes and torsion bars!
Old 08-14-2003, 01:07 PM
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Thanks for the info Rob. Im planning on getting a 2nd hand set of spring plates to refurb.

Looking forward to seeing your progress. Light at the end of the tunnel!
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Old 08-14-2003, 01:35 PM
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I am really worried about this. I found myself in the garage last night, looking through my plastic bags of removed parts for things to have plated. Then I began inspecting the front suspension, which I thought I'd finished weeks ago, looking for fasteners and other things to remove and replate. But if you refinish one part, don't all the other parts around it suddenly look intolerably shabby? I am now even thinking about removing my heat exchangers / cat converter for Jet-Hot coating. This all started with a simple tire change. Where does it all stop? When will I drive my car again? Help me!
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Old 08-14-2003, 01:51 PM
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I'm afraid Noah is absolutely correct! My sickness started with (what I thought was) a sticking caliper due to old rubber brake lines. Once I began, I've totally gone off the "deep end", and here are some of the results...930 calipers, rotors, Sanders hollow t-bars, Elephant Racing bronze bearings, etc, with the front suspension refreshed and with everything powder coated and replated. Here's a couple of shots showing the gold cadmium plating on the spring plates vs. the yellow zinc on the rotors. Help me!!!
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Old 08-14-2003, 05:56 PM
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oooo, those are luverly . . . feels like a trip to the jewerly store. Thanks a lot, you've just cost me some money!
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Really want to find a clean E28 . . .
Old 08-14-2003, 09:38 PM
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