Is the shaft supposed to be spring loaded? Or is the only spring action at the contact brush itself?

A friend brought one over, has to be 50 years old or more, hadn't been apart any time recently since all the screws were very dirty. Problem is the main shaft attached to the knob moves up and down 1/2" or more, which it shouldn't, and there is no output. That's because the brush isn't anywhere near the top of the windings.

Upon finally being able to get the knob off and remove the cover, the screws on the round upper disk were tight and dirty, the brush sits about 1/2" above the windings unless you force the shaft down and hold it. Doesn't look like the lower collar on the bottom has been moved since you can't get to the screws without taking the shaft halfway out of the unit. Can't see any reason why the 1/2" motion in the shaft should be there. If you force the shaft down, the brush will touch the windings.

I wonder if someone had it apart decades ago for some reason, couldn't figure out what they were doing, and reassembled it with something missing, or if they just reassembled it wrong. With the screws all as tight as I found them, there's no way that something just slipped, either it was done by mistake or there is a part missing. The wiper contact at the top which fits underneath the round disk looks to be intact and in the right position to work.

Every vintage Superior model 116 (anywhere from late 1950's to present) I've seen has some type of ring or "circlip", a large circular springed tempered ring that fits a small groove on the shaft's bottom which keeps the shaft from riding up and allowing the wiper contacts from going off the windings. The circlip needed here is an "outy" so it will hug around the shaft's machine groove. Other 116's I've seen have instead simply a drilled hole (about 1/16" diameter) thru the bottom of the shaft, that has a rolled or solid metal pin holding in place a white nylon circular thick washer/bushing, which keeps the shaft from riding up. Look very closely at the shaft's bottom, as it should either have a machined/lathed groove near the bottom that accepts the proper-sized "outy" circlip from your local hardware store, or a hole drilled thru the shaft, for a pin and a thick insulator washer above that. I think it's missing from yours. Without this circlip or pin-w/thick plastic bushing in place, then the shaft will ride up like you've described, and its phosphor-bronzed springed wiper contacts will not make contact with their windings. The true "Variacs", made by GenRad, instead used a wedged carbon wiper brush backed in a metal rectangular-vertical well, backed by a strong coiled spring which is isn't nearly as sensitive as a Superior-brand to getting the exact shaft height , and the Staco-brand (DaytonOH) variacs used again another design of wiper contacts, I forget exactly what as I don't have a Staco torn apart right now. Of the U.S.-made variacs, only the Superior brand variacs used the phosphor-bronze leafed wiper springs, and the shaft has to ride at precisely the correct height, otherwise the wiper contact won't touch at all or it will wear out the windings in no time flat if the shaft is riding too low. If its main shaft is rusted, then the small groove may be filled with rust; you'll need to search for the groove.

This one has no snap ring, only a steel collar underneath the unit with two allen screws that can't be reached with a tool because the whole collar fits deep into the recess in the base. Looks like the position of that collar has to be set before the top rotating disk with the brush is positioned on the shaft, no way to adjust it once the shaft is installed in the unit.

Makes me wonder if someone several decades ago replaced a missing snap ring with the steel collar, and didn't reassemble the unit correctly? This came out of a professional/commercial lab, still has the 50's ID tag glued onto the switch housing. No telling what the "engineers" at one of those places could have done.

I know this thread is a little old, but I thought it might be helpful to resurrect it and add what I learned today, since it seems directly relevant.

I listed three uncased Superior 116s, over in classified, with the caveat that I didn't want to power them up due to the lack of an isolation transformer.

Tom (Nortronics) was kind enough to post a connectivity diagram, along with some tips on testing with a DMM. Two were fine, but the third had a similar problem to that which Dennis describes (though not as extreme as a 1/2"). For clarity, I'm describing the variacs resting on the cast base, with the shaft vertical.

After reading this thread and examining all three, I found the following:
- All three have the roll pin and bushing arrangement that Fred describes.
- The two "good" ones had a small amount of vertical play on the shaft (less than 1/4") with the slack being taken up by the spring action at the brush.
- The third one had a similar amount of play in the shaft, but unless the shaft was pushed down the brush stood proud of the coil.

The solution appeared to be to loosen the two grub screws holding the disk with the brush to the shaft, then pull the shaft up, while pressing the disk down, until the brush made contact (with the spring mechanism in a similar position to the other two) then tighten the grub screws back up.

I did that and now all appears to be well - I'm getting continuity between 1 and 3 and am now off to note down resistance values (because I'm like that).

I had one of these and due to it's weight and apparent movement during shipping it seemed the wiper connection had slipped. It's a matter of loosening the collar and validating continuity across the whole wiper range - prior to tightening the screws again.

JP

I ended up having to push the shaft out the bottom far enough to loosen the allen setscrews in the round metal collar and move it up further on the shaft. No evidence there had ever been a pin. After moving the collar, then I was able to reassemble the parts on the top end at exactly the same location down from the end of the shaft that I found them, and where the only setscrew marks were. It was close, there was a little tension on the contact but one or two dead spots as it was rotated. Readjusted the wiper assembly a bit further down and it worked fine. Either this one had originally been built with a metal collar at the bottom end instead of the pin or clip, or someone decades ago had put the collar on there. There was enough dust and dirt in and on the unit that there was no doubt it had not been touched in a long time.

After thinking about this a while, another possibility comes to mind. What if the original shaft for whatever reason had snapped off at the groove where the clip fit into it, and someone just replaced it with whatever shaft they could come up with, using a metal collar on the bottom end?