A good number of the Suntour Bar Con shifters I see on bikes or on Ebay have the smooth exterior pivot nut (for the lever) missing. The inner nut fits into a six-sided shaped slot in the housing. With that nut snug in there holding the pivot bolt, is the outer nut mostly cosmetic, or is it really needed as a locking nut? The back sides of them are smooth.

I also figured the nut you're referring to was mostly cosmetic but My shifters didn't hold in gear properly without said nut.

The ones that I use on my bike seem to need the nut, also. I'm selling some on eBay that are complete, too...

It's needed as a locknut. Without it, the rotation of the shift lever will work the pivot screw loose. Without enough screw tension, the lever won't hold its position.

Yup, it's necessary, plus it's a lousy design, hence the many missing ones.

Neal

I believe you all, but I don't see how the outer nut works as a locking one. With a smooth back, the only grip it has anywhere are the threads that go onto the bolt. Can someone explain how just those threads on the outer nut keep the bolt from turning? It's not rocket science, so I know I can understand it somehow, but that outer nut on that bolt doesn't make sense to me as to be locking.

I can't explain the locknut dilemma, but I've fabbed replacements from a panhead screw. Drill a hole in the screw slot, cut the shank off the screw, stick the head in a vise and tap it for a 4m (someone correct me if I'm wrong on that size). Then use a bit of blue loctite when you put it together.

Use blue Loctite before they fall off and get lost. I used to put a piece of clear tape over mine, but it looked tacky.

I'm 100% with you. I didn't understand it, and I was really resistant to the idea of that being the problem with my set of Barcons. Mine didn't work without it and when I replaced it, it worked. I still don't understand it....I just did what worked and left it at that.

If yours manage to work without it, just go without it.

Thanks for the work around idea with the panhead screw due route. If I come across some Barcons that need those nuts that is an option. I wonder if anyone here has discovered an off the shelf threaded nut that solves the problem. If so, what sizing is that little nut?

4M and file off the corners. File a slot down the middle to screw it on.

The pair on my UO-8 is missing one outer nut, so I am running half-step gearing w/ no locknut on the front shifter. I have had no issues w/ unintended downshifts. Another option for those missing the locknut and experiencing loosening would be Loctite on the hex nut, although I have not had to resort to this. I do use Loctite on Italian and French fixed BB cups, however.

Loctite! Why didn't I think of that?

is there an echo in here?

I'll try. If you screw two nuts onto a bolt, then tighten them together, you can lock them anywhere on the threads you like. Since the inner nut on the shifter is trapped in the housing, the outer nut locks the screw in place after it has been tightened the right amount. The two nuts push together when the outer one is tightened. They pull and distort the thread on the screw very slightly, just enough to keep it from turning when the lever is moved. The distortion is temporary: as soon as you loosen the nuts, the screw returns to normal and can be turned.

Right! Phrased another way, as the two nuts are tightened against each other, they are forced to push against the threads of the bolt in opposite directions from each other. The tighter they are tightened, the more friction there is between the bolt threads and each nut. That friction prevents either of them from rotating in either direction. Without a locknut, the friction between the bolt threads and the one nut is very small, and that's why the bolt will continually work its way loose.

Those explanations make sense, thanks.

Now i have to go check my barcons.

I have a bigger problem with my Simplex Retrofriction bar end shifters. The locknuts are not slotted and they're inset so that I can't get a wrench on them to tighten them adequately. I think I'm going to have to grind a socket thinner.

Inadequate design but probably a compromise. I wonder how many set sit languishing because of lost lock nuts. I have a pair downstairs. And, the slotted head lock nut really needed a special tool to tighten it, no? Something like a crank bolt wrench or a large screw driver with a relief slot cut into it for the bolt. I'm going from memory here.

Yes.

I have a Suntour Barcon with the end of the bolt snapped off (from me overtightening the locknut). So, it threads the first nut, but it's too short for the locknut. I wonder if loctite would be sufficient to hold the nut from turning loose?

If a second nut on that bolt is necessary for better performance of the shifters, I've got a public service announcement here.......

I'm still trying to track down a candidate nut that will fit that I can cut or file a slot into, but in the meantime I found a small hex nut at Home Depot that fits on the bolt. I believe the size is a M4-7 or M4.7. It is not as wide across as is the original, but it fits on the bolt and applies pressure on the other nut.

Package also reads: 18-8 Stainless Steel Br-M / 12-M. A package of two cost me 50 cents plus tax. Found them in the sliding drawers.

I have used stainless Acorn nuts I bought at my ACE to replace the round slotted nut. M4 IIRC. Not exactly perfect, but a working alternative.

"Those locknuts are a very commonly lost/damaged part, and have not been
available for decades.

As it happens, there is a relatively easy workaround. Many pedal
reflectors use 4 mm threaded hardware, with nuts that use a 7 mm wrench.

The 4 mm thread is the same as the Barcon pivolt bolt, and the 7 mm size
is small enough to let you use a nutdriver or socket wrench to tighten
the nut up inside the recess in the Barcon housing.

Most bike shops will have a box full of discarded pedal reflectors under
a counter somewhere..."