Weird Noise and Vibration from Distributor?
 

1980 911sc, unknown mileage.

In the last 100 miles it started to develop this weird, random, intermittent shudder at idle accompanied by a high pitched buzzing sound. Don't notice it when under load or moving, but at idle it comes and goes randomly. The noise/vibration can be a quick chirp, or more recently can last a few seconds.

I removed and had a shop rebuild the alternator. The shop said the front bearing was toast, so I figured that should take care of it. Reinstalled it last night, and the noise remains.

Now when it happens, i can feel the distributor vibrate a ton and it feels and sounds like that's where it's coming from. I took the cap off and it all looked fine, the rotor could move a little bit, but I'm not sure how much is acceptable.

Here's a video I took last night - https://youtube.com/shorts/ELqbla47qfY?feature=share

I don't want to drive it in case it's damaging something further. Any thoughts?

Not sure but it might be that the ignition distributor bearings are bad and the rotor is hitting the cap. Easy to check pull the distributor cap and inspect.

Just a guess.

How much vertical play is present in the distributor shaft?

Is the cap on tightly? It should be mounted firmly with no play. You may need to tighten up the clips, and check that the screws that hold them in place are tight.

you absolutely sure it isn't the cooling fan touching the shroud? That noise is common and sounds like an intermittent chirp when it first starts to occur.

Had one years ago where the brass distributor drive gear on the crank was loose.

Remove the distributor cap. Pull the distributor shaft up & down. Then rock it back & forth. There should be no (or very, very, very little) movement in either plane. The contacts in the cap should be un-marked by the rotor.

i`d start by removing the alt.belt and see if the noise is still there..it totally sounds like alt bearing-dry....remove it and report..also use a long screwdriver ..one end to the alternator prior removing the belt.(also one end to the distributor cap) and the other end to your fist and put you ear against it to listen..also you could use stethoscope if you have one...

Ivan

Sorry for the delay guys.

Did a little more testing here -

-Removed the alt belt and noise remained.
-Can visibly see and feel the distributor cap vibrate when the noise happens
-I believe there are marks on the cap where the rotor may be contacting the contacts
-Pulling and pushing the rotor does yield a little movement side to side, and I can pull the rotor up and down at least 1/4"

I think this distributor has to come out for inspection. Taking it to the shop on Friday to get in deeper.

I finished rebuilding my distributor and it csm out great. It had a lot of movement in all directions. It now is solid. There are kit that include all the bushings, seals, spring and screws. PM me for my source for the parts.

Partz classique.