Distributor Question - The "Contactor"?

[Captain Obvious]

I've got my distributor off my 77 because I've been messing with my oil pump, and while looking it over, I noticed a curious little nubbin I did not recognize. Upon consultation with the FSM, it's called "The Contactor".

Here's some snippets from the 77 manual showing the little beastie:

Ok, so the intention is to prevent hysteresis in the advance mechanisms. Fair enough. But what the heck? Is this simply some small amount of intentional friction to keep the thing from floating on any play in the system?

[Captain Obvious]

Nuthin'? Nobody has ever noticed this thing before? I'm the first?

Nobody has any idea what it's supposed to be doing in there?

[Zed Head]

I've noticed it and adjusted it, but have not seen the text about the hysteresis prevention. Pretty interesting, thanks for illuminating. Looks like it's a drag or brake on the shaft while the reluctor tooth passes the pickup coil. To make sure that the "slack" is taken up and the pickup doesn't trigger early, maybe. If the rotor bounced ahead the timing could be advanced. Should also keep any play in the shaft pushed to one side, keeping a constant gap between the pickup coil and reluctor teeth.

Weird that they used a four tooth reluctor to show the air gap measurement, and a six tooth below that.

[Captain Obvious]

I was looking at this thing in a little more depth yesterday, and something that's interesting is that the "contactor" contacts when the ignition pickup is about mid-spaced between reluctor teeth. In other words, the contactor does not hit the cam lobe at the same time the reluctor is passing over the pickup, but in fact contacts about 180 degrees off that.

Makes me wonder if they were expecting the reluctor to be pulled ever so slightly towards the magnet inside the pickup when the gap is small, and they provided the contactor to produce the same effect when the gap is at it's largest. WAG...

Yeah, and funny about the number of teeth on that reluctor. Neat little typo you caught there.

[Dave WM]

just came across this old thread while researching noise from my dizzy. Funny I have a couple dizzy spares some seem like you can feel the notchyness of the contactor other one none, prob just worn nubby thing. I took the noisy one apart, cleaned and lubricated the shaft, reassembled and reset the gaps (reluctor and contactor). still notchy but not noisy like before. I presume the thin layer of grease accounted for most of the noise reduction. Along those lines I noticed a sprial cut in the drive shaft, I presume for moving lubricant around. Not sure if the grease was a good idea. Maybe the intent was to suck up some residual oil that always seems to be in the bottom of the cup where the dizzy bolts on to?

 

Edited May 22, 2023 by Dave WM

[Dave WM]

My guess based on the FSM mentioning the advance mechanisim and hysteresis is the rubbing block is supposed to counteract the torque applied the the bracket that is supported by the 3 ball bearings that allows the pickup coil to shift when the advance mechanisim is active. That is the magnetic pull of the pickup coil is transfered to the movable mount, and the contactor offsets this pressure in the opposite direction. Anyway just a guess.