Points Distributor: RFI 2-Pioece Clamshell Shielding Necessary?
Thread Starter
Pro
Joined: Jan 2004
Posts: 653
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From: TX
Points Distributor: RFI 2-Pioece Clamshell Shielding Necessary?
I'm talking about those 2-piece round clamshell shields that go inside the distributor cap, under the mechanical advance and over the points. I assume these were originally installed for possible RFI noise from the points? Or was it overkill and not necessary?
This would be on say a 1971 using breaker points and *separate* condenser? With an additional 2nd capacitor attached directly to the coil and the original chrome ignition shielding in place? Will an original Delco AM/FM radio still pick up up RFI without the 2-piece internal clamshell?
My Delco radio doesn't pick up any RFI whatsoever from my current Pertronix setup. But if I switch back to points, was wanting to know what other 'baggage' comes with them (esp w/ separate condensor w/ wire lead). And these shields don't seem to be commonly available. I get the feeling they've been widely discarded over the years which makes me wonder if they were ever all the necessary in the first place. (Or also uniset points would also mitigate this I suppose.)
Thanks,
This would be on say a 1971 using breaker points and *separate* condenser? With an additional 2nd capacitor attached directly to the coil and the original chrome ignition shielding in place? Will an original Delco AM/FM radio still pick up up RFI without the 2-piece internal clamshell?
My Delco radio doesn't pick up any RFI whatsoever from my current Pertronix setup. But if I switch back to points, was wanting to know what other 'baggage' comes with them (esp w/ separate condensor w/ wire lead). And these shields don't seem to be commonly available. I get the feeling they've been widely discarded over the years which makes me wonder if they were ever all the necessary in the first place. (Or also uniset points would also mitigate this I suppose.)
Thanks,
Thread Starter
Pro
Joined: Jan 2004
Posts: 653
Likes: 56
From: TX
... did a little more digging - according to some online sources the internal shielding clamshells started appearing around 1970 or so and was potentially added for (non-Corvette) passenger cars that started getting those tiny antenna wires embedded in their windshields. Perhaps Corvettes just got those clamshells like everyone else in the GM world to simplify distributor production even though Corvettes still had the traditional whip antenna. If so - that suggests these internal clamshell shields probably aren't essential in early C3s (with points and Delco radio) afterall.
Last edited by C8H18; Mar 7, 2025 at 08:18 PM.
Melting Slicks
Joined: May 2021
Posts: 2,281
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From: Fleming Island, FL
While I don't have a answer for you I have a little tidbit. The 1970 AAR Cuda and the T/A Challenger had their antennas in the right rear quarter instead of right front fender. Chrysler felt that the fiberglass hoods on those cars that the ignition would cause radio interference.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Not necessary.... IF the other [stock] RFI hardware on the engine is still in place. And you don't want TWO active condensers in the distributor ignition system. Either keep the combination unit and remove the stock condenser, or do the reverse of that.
Race Director
Joined: May 2006
Posts: 18,755
Likes: 2,589
The second capacitor is the stock unit mounted to the side of the coil for radio interference and is not related to the condenser inside the distributor connected to the points
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Thread Starter
Pro
Joined: Jan 2004
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From: TX
But (outside of the distributor) there is another condenser or capacitor for the purpose of mitigating RFI in radio equipped Corvettes that is mounted to the coil bracket and also connected to the coil. In fact there are also several more of these elsewhere on the car including above the steering column (turn signals) and voltage regulator...
Burning Brakes
Joined: Apr 2020
Posts: 792
Likes: 422
From: Western NY
Interesting you bringing up those shields. when I first got my car in 81 I let someone tune it up and when he put new points in he did not replace those shields. kinda pissed me off and I never saw them again. I've never even seen them listed anywhere as a replacement part for a distributor nor have I even heard mention of them until this thread. anyway I had no problems with radio noise without them.
Pat
Pat