I always wondered about it, and the people who reproduce the rotor dust covers even today do not seem to know why.

Years ago I investigated and then found the reason and then set out to find a pair of NOS factory Chevrolet Delco front wheel hub noise "static collectors".

What they are is a matched set of a brass coils for installation in each of the rotor hubs.

The coils were designed to eliminate electrical interference generated from the motion of the hub and bearing assembly, so the front wheel hubs used these cone shaped springs known as "static collectors". eliminating radio noise induced into the cars AM radio from the front wheel bearings.

Rotor

Rotor assembly

The Static Collector head rides against the lathe tip and the rotor dust cap. The dimple was designed to catch and hold residual grease flung out of the bearing away from the static collector.

Very interesting. A lot of engineering went into that little assembly just to make the radio sound better.

Nice article Phil. I was also wondering about the static collectors. Were they installed on all radio optioned cars or were they a separate option altogether?

Only on disc brake cars

Here is the visual