EPDM coating

[hotrod68]

  I'm curious--is the black EPDM coating (primer/sealer?) that GM uses today on components the same kind of coating that was used in '68? I hear and see endless speculation on the correct "gloss" for subframes, radiator supports, inner fenders, A-frames, rear axles, etc... NOS GM sheetmetal and many new car parts still come with this coating, and it occurs to me if select parts were EPDM coated back then, a lot of the mystery would be taken out of the correct "sheen" controversy if EPDM is in fact the same stuff from the Old Days. I know different parts have different degrees of gloss--a bumper bracket may be gloss black and a fender will be EPDM, but surely there was a pattern... Is this a valid speculation or is my logic all wet?   

[firstgenaddict]

Items like bumper brackets were manufactured by outside vendors and may have been painted a variety of shades of Black.
My bumper brackets are a warm black not a cool black like the inner fenders... the best thing to do is document and research as much as possible.

[JohnZ]

There were many different (paint) coatings, and many different gloss levels of black. Items like the subframe and control arms were painted by their suppliers, and parts like bumper brackets, engine accessory drive brackets, rear shock plates, and things of that nature were received raw and were dip-primed or flow-coated with black primer after cleaning and phosphating at the assembly plants. Front sheet metal (hoods, fenders, headers, valances, inner fenders, radiator supports, grille supports, etc.) were also received raw, and were dip-primed or flow-coated with black primer after cleaning and phosphating.

There's no "EPDM" coating - what you're referring to is "E-coating", which was the successor process to dip-priming and flow-coating; E-coating is also a dip-prime process, but uses positive and negative electrical charges in the paint and on the parts to get a more uniform coating.

Service sheet metal in the 60's was shipped raw in racks from the stamping plants to the Regional Parts Depots; each depot had its own dip-prime system for painting those parts before boxing them for storage, and that same method is used today, except the old dip-prime systems have been replaced with E-coat systems.

[hotrod68]

I meant E-coat, John--brain fart. So if I understand you right, the coating GM uses now is NOT the coating of old? I was referring to parts as they come over the counter in boxes, and the GM NOS sheetmetal still comes with the black coating. And that begs a good question; is the NOS stuff still available from GM REALLY new old stock, or is GM selling in-house repro parts through it's delaerships as NOS? The aftermarket stuff has what looks like an identical E-coat to the old GM parts. Just curious.

[JohnZ]

The old coating for service sheet metal parts was dip-prime, the current coating is E-coat. I'm not familiar with the parts currently being sold over the GM parts counters.