Downtube shifter bosses with small square - Possible to mount indexed DT shifters?
 

I'm building up a 1981 Nishiki International as a vintage-y allroad bike. 33mm 700c tires with fenders.
Was planning Shimano indexed downtube shifters for initial build. But turns out the shifter bosses differ from standard (edit: Type A) shifter bosses. The bosses are very similar, with the same diameter (~9mm) and thickness of the flattened section (~6mm).
But the raised square at the base of the shifter boss is a different size. On standard type-A shifter bosses, that is 12.2mm square. On this Nishiki, the base is 10.2mm square, and also doesn't stick out quite as far from the frame. The boss takes 5mm screws (like standard type-A bosses, but with slightly different threading pitch), not 4.5mm screws like the Shimano type-B.

edit: Note that this is different from the type-B shifter bosses that Shimano used in the early 1980s - those had a curved base and a tab toward the front.
These bosses came with Suntour friction shifters, and are probably Suntour bosses. That would have been a better subject-line term.

The only ways I can think of to mount Shimano indexed downtube shifters are
a) find some holy grail curved baseplate designed to seat on these bosses. I doubt this was ever made.
b) use clamp-on DT shifters and leave these bosses hanging out ugly and naked.
c) use Suntour power rachet shifters that match/fit the bosses. Not indexed, but easier to use than traditional friction.

The better solution is probably just use bar-end shifters, as I was considering anyway. I'd need to find an appropriately-threaded screw to hold cable stops on.

The following photos show a standard shifter boss with 12.2mm square, and odd shifter boss on the Nishiki with 10.2mm square, and the original friction shifters that came on the Nishiki.

https://cimg5.ibsrv.net/gimg/bikefor...51427680f6.jpg https://cimg7.ibsrv.net/gimg/bikefor...ec707d585b.jpg

https://cimg6.ibsrv.net/gimg/bikefor...2aba613296.jpg

Maybe this link will help:
https://www.bikeforums.net/classic-v...-shifters.html

Thanks. I've worked with the Shimano type-B shifter bosses before (curved base and tab pointing toward the head tube). I was repainting the frame, so I ground down the boss (careful to avoid the tube) so that a typical downtube cable stop would fit over them, and then just affixed them with a 4.5mm screw. Reading these helped me get the terminology of Type A and Type B (and their histories) correct.

These bosses on this Nishiki are different. More visually similar to Campy type-A standard. I edited my original post to include proper terminology.

These bosses came with Suntour friction shifters, and are probably Suntour bosses. They match the mounting structure for some Suntour stem shifters that I have sitting around, too. I could also use Suntour power rachet (non-indexed) downtube shifters.

I could only find two threads where it appears someone is dealing with Suntour type of shifter boss, and there's nothing systematic contained in either thread. Thread 1. Thread 2.

This thread is limited by the lack of clarity in my subject line, because I didn't know how to describe the bosses when I wrote this. If discussion doesn't take off here, I may write another post later about Suntour shifter boss standard.

The shim might help, but I don't think it would work to tap 5mm threads over to a slightly different 5mm thread pitch. Tapping 4.5mm threads (for Shimano type-B bosses) to 5mm would probably work because you'd be widening the hole in the process, but there's no extra material to wrk with in this case. But I can just use the bolts that came with these suntour shifters (or find something matching at a hardware store).

I think the etiquette would be a PM to the OP.

(Private Message to the Original Poster)

+10 :lol:

How do you know she doesn't?......

This is what 3d printing is for. You may even know somebody who has one.