65/66 power antenna mounting bracket screws

[Gary B.]

For 1965 and 1966 there are 3 screws that secure the power antenna bracket thru the rear wheel well fiberglass to a nut plate with 2 welded nuts, and the base of the motor of the power antenna. The ‘65 AIM specifies GM # 9418423 for all three screws. The ‘66 AIM has a hand-written item designating 9418423, plus a normal font item designating screw 3830946. In the AIMs, these screws are referred to as “Screw Asm.” because they consist of a screw with an captive lock washer or captive flat washer. The attached photo shows two of the three screws that I removed from my ‘66 that I believe are original to the car. Two of these screws have an indented hex head, 1/4-28 threads, and are 3/4” long. (The 3rd screw is the same as the one with the captive flat washer, but is 5/8” long. I’ve been told the shorter one screws up into the bottom of the power antenna motor housing and has to be shorter in order to not interfere with something inside the housing.) The screw with the lock washer has a headmark consisting of concentric circles. A prior posting on the DB suggests there might have been the letters ELH within the innermost circle, but those are not visible on my example. The screw with the flat washer has an anchor headmark, with three short lines.


Joe Lucia tells me these screw assemblies were never available in service, and therefore I can’t tell which GM part number goes with which screw. Can anyone help me determine which of these screws is which GM part number? To the best of my knowledge, in ‘66 those screws were used nowhere else on the car.


Finally, I can tell by the imprint of the lock washer in my original antenna bracket that the screw with the lock washer was the upper screw attaching the bracket to the nut plate, thru the rear wheel well fiberglass. The screw with the flat washer must have come from where the ground strap attaches at the lower hole of the wheel well portion of the antenna bracket.

Does anyone know if these were black phosphate? Or zinc? I’m guessing black phosphate.

Thanks,

Gary
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[Robert P.]

Re: 65/66 power antenna mounting bracket screws

Gary , found my original lower mounting bolt sent you a few pictures
regards Bob

[Gary B.]

[David B.]

Re: 65/66 power antenna mounting bracket screws

GM part #9418423 is 1/4-28 x 3/4 hdr. pt. plain GM 275-M Machine screw and helical spring lock washer (large hex head)

[Keith B.]

Re: 65/66 power antenna mounting bracket screws

here is a picture of the mounting hardware supplied in a NOS antenna kit
pa4.jpg

[Gary B.]

Re: 65/66 power antenna mounting bracket screws

GM part #9418423 is 1/4-28 x 3/4 hdr. pt. plain GM 275-M Machine screw and helical spring lock washer (large hex head)

David,

Thanks very much for the screw specs. Can you tell me what the spec “hdr. pt.” means? Something about the point end of the screw. Also, what does “large hex head” indicate? Could the screw at the left in my first photo be 9418423?

Gary

PS. I just found this online: “Header Point; Produced during the forming operation. There is a small chamfer that is added to the screw blank. When the thread is added to the screw blank. This small chamfer produces a smooth transition between the point and the thread.”

Both of the screws I show in the first image in post #1 appear to have a small chamfer at the tip, which suggests they have header points.

[Gary B.]

Re: 65/66 power antenna mounting bracket screws

Keith,

Are the two screws stuck in the cardboard your original ones? And all the loose items are from the NOS kit?

Gary

[Keith B.]

Re: 65/66 power antenna mounting bracket screws

If I remember that is not cardboard but a metal plate with a protective film on it. All the screws pictured came in the box with the antenna. It came with everything to add a power antenna to a non radio car.

[Gary B.]

[Alan D.]

Re: 65/66 power antenna mounting bracket screws

Late addition however, may help future users doing a search Most other posters already have the print

[Gary B.]

Re: 65/66 power antenna mounting bracket screws

here is a picture of the mounting hardware supplied in a NOS antenna kit
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[Keith B.]

Re: 65/66 power antenna mounting bracket screws

Keith,

Am I correct that the NOS power antenna hardware kit you show was sold by GM? Do you know what year it dates from? I’m trying to learn when GM made a star washer with both internal and external teeth.

Gary

Here is a picture of the broadcast sheet that was in the box. I am not sure when it was sold

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[Gary B.]

[Keith B.]

Re: 65/66 power antenna mounting bracket screws

the date at the top is: 03156. So is that March 15th 1966? The part number is 3864187. Maybe Joe will read this and tell us when it was in service.

[Gary B.]