Rocker Molding Retainer Screws finish???

[James W.]

Looked through my 1963/1964 and 1965 judging manual and can't find any reference as to what the correct finish is (silver zinc or black phosphate) for the rocker molding retainer screws. This is for my late production 1965 coupe. Picture of the repro on the left and what I removed from the car on the right from my '65 that has been owned by my family for 50 years.

Thanks,

James

[David B.]

Do you have a part number?

[Gary B.]

David, James,

Probably GM 3848300. Based in what I’ve read and seen first hand, repros tend to be zinc. GM examples that came with MOS retainers tend to be yellow/gold dichromate. My guess is that originals were black phosphate or dark, natural. Rich Pasqualone has said black.

Gary

[Tom D.]

I think... these along the bottom?

[James W.]

I think... these along the bottom?

No. There are six (6) total on each side to retain the rocker molding retaining strip. The U-nuts or clips are black phosphate, but I am trying to determine the screw finish. As you can see the repro is zinc plated.

James

[James W.]

Do you have a part number?

The screw is part number 3848300 and the U-nut is 3846854.

[Gary B.]

I think... these along the bottom?

Tom,

The screws go in horizontally, holding the retainer to the fiberglass. They are not the screws that go up from the bottom, holding the rocker molding to the frame brackets.

Gary

[Gary B.]

Yes, six (6) total on each side to retain the rocker molding retaining strip. The U-nuts or clips are black phosphate, but I am trying to determine the screw finish. As you can see the repro is zinc plated.

James

James,

In the ‘64 thru ‘67 AIMs those rocker panel retainer screws, 3848300, are the exact same screws as for the wiper grills. They are dark, probably black phospahte. Not zinc and not dichromate. If you search the archives for 3848300 you can read what’s been said before.

Gary

[James W.]

James,

In the ‘64 thru ‘67 AIMs those rocker panel retainer screws, 3848300, are the exact same screws as for the wiper grills. They are dark, probably black phospahte. Not zinc and not dichromate. If you search the archives for 3848300 and you can read what’s been said before.

Gary

Gary,

Did some digging and found a post that discussed them with pictures that match what I have. Looks like what I took off the car last month are the factory installed screws and U-nuts with the "P" embossed into them. Will bag and tag them to be finished on black phosphate. Since we've owned this car for 50 years, I doubt my dad ever replaced them when he had the car repainted in 1977.

Thanks,

James

[Michael G.]

I doubt that they are black phosphate, that finish would rust after the first rain in such an application. Fisher Body/Chevrolet had, in those days (and may still use something similar, I don’t know) a black exterior body finish (GM-6138M) that has multiple electroplates, followed by a black paint coating, for such applications. It lasts essentially forever.

I don’t know if you can still get that finish, I doubt it, but instead I’d recommend you get the parts cadmium plated, (which will get you much better corrosion protection than zinc chromates) then spray them black yourself (after being on the GM fastener finish committed for many years, that’s what I do). That’ll last longer than you own the car.

[Ron G.]

During all my years of research I believe that the 68 - 72 screws for the rocker mouldings are plated black oxide. This is opinion for the door sill plates as well. Although, 99% of all hardware that is plated black is usually plated black phosphate, the reason I believe that the aforementioned are plated black oxide is that they are visibly seen and is more eye appealing. Years ago, when I was researching with assembly line procedures and having conversations with GM employees, I was informed that they did use black oxide for some of their hardware. Hope this helps. - Ron

[Michael G.]

During all my years of research I believe that the 68 - 72 screws for the rocker mouldings are plated black oxide. This is opinion for the door sill plates as well. Although, 99% of all hardware that is plated black is usually plated black phosphate, the reason I believe that the aforementioned are plated black oxide is that they are visibly seen and is more eye appealing. Years ago, when I was researching with assembly line procedures and having conversations with GM employees, I was informed that they did use black oxide for some of their hardware. Hope this helps. - Ron

Ron: I don’t know what you’re referring to as “black oxide”, but the finish GM referred to as ”black oxide” was used on exterior fasteners, but ONLY on stainless steel screws, as it lent NO corrosion protection whatsoever. GM had many fastener finishes designed for exterior use on carbon steel screws, black oxide was not one that was ever used in such an application. It is possible that GM-6138M was used, which has a smooth black oxide-type coating, applied over several electroplates. Black oxide alone will NOT work in such an application.

[Ron G.]

Sorry, I was referring to the 68-72 models with emphasis on the 70-72's.

[Alan D.]

Jim, I vote for the one on the right. As far as I can remember these are on my 64 (not going to take rocker Off)
Believe the screw is pn 3848300 and U-Nut pn 3846854, have not found yet in any of my books. Sorry still not use to this new format: top or bottom ????

[James W.]

Jim, I vote for the one on the right. As far as I can remember these are on my 64 (not going to take rocker Off)
Believe the screw is pn 3848300 and U-Nut pn 3846854, have not found yet in any of my books. Sorry still not use to this new format: top or bottom ????

Alan,

Yes, the screw and U-nut on the right are the ones I removed from the car and soaked in EvapoRust. There was evidence that my dad had them off in 1977 when he repainted the car. He had cleaned and painted the the rocker molding retainers dull silver. The screws and U-nuts were as-found when I removed the rocker moldings a few months ago to begin prepping the car for flight judging.

James