older dt-shifter braze-on - work with indexed dt shifters? (pictures)
I've got a Centurion Comp TA from 1984, and am getting it sandblasted and repainted soon. The downtube shifter braze-ons are different than I've seen on any other bike, having a "stop" built into them rather than being part of the curved-spacer piece that sits between the frame and the shifter.
I think this precludes the use of indexed down-tube shift levers with this frame, because the right (rear) indexed shift lever requires a spacer that can't fit over the braze-on of the TA Comp. The bike came with Shimano 600 components including pure-friction (no racheting) down-tube shift levers, that worked perfectly well with the brazed-on shifter mounts on the frame.
I'm guessing that I can't use indexed down-tube shifters with the braze-on mounts on the TA Comp. No biggie - I'd probably have planned to use bar-end shifters even if the down-tube mounts were normal. But it's nice to know one's options.
1) a normal down-tube shifter braze-on, without the curved spacer.
2) normal braze-on with the curved spacer from Shimano indexed down-tube shifters
3, 4) TA Comp braze-on
5) TA Comp braze-on with aluminum spacer press-fit over the braze-on.
Why not try it and see? If you can get the tabs to engage, it should work correctly. No need to build it up or anything, just see if you can install the lever and get it to click. Those Shimano DT shifters don't seem to be all that picky. I'm going to try and get one to work on a clamp-on band for a bike without braze-ons. Now THAT might be weird!
I did try, and the indexed shifter has nothing to engage with to lock it down (the stop isn't what locks it down). I'm going to see if the place can grind the things down or completely off before repainting the bike, because the shape of these things can't even accommodate the cable stops that screw into down-tube shifter braze-ons. The tab gets in the way, but even apart from the tab, the mount has that wider circular part at the base that gets in the way.
Sorry, should have been more clear with my first post.
Okay, here's the deal: the place that's doing the sandblasting and powdercoating is going to grind down the shifter braze-on (both the forward tab and that lower, wider-radius bit) so that a downtube cable stop (designed to bolt into standard dt-shifter braze-ons) will fit over it, flush against the tube.
It's possible that in the process of grinding it away, the brazed-on piece will fall off (because the brazing material itself may be concentrated toward the outside of the interface between shifter mount and downtube) and if that happens the place will just sand the tube down so it's smooth before painting, and I'll use a clamp-on downtube cable stop.
That would have been my solution, but I wouldn't trust anyone else to do the work. I'd do it myself, but that's just me and I have the tools. After some recent experiences I've had with auto mechanics and home improvement contactors, I don't feel like I can trust anyone to do anything right the first time.
Looking at the picture of the red frame I think that the braze on will fit the early '80's ornate Shimano 600 friction shifters. I ran into this problem with a old Velo Sport road bike I had. If you can find a donater bike I would remove the braze ons from it and have them welded onto your Centurion. I've also used a Suntour downtube clamp on shifters band and used Shimano levers and it worked good. Also check Ebay for Shimano clamp on index shifters. They pop up once in a while.
Brazing the right bosses onto the tube is a simple operation, the old ones can be removed by keepig 90% of the heat on the bosses and the new ones attached witn low-temperature silver. Unless done with too much heat it shouldn't weaken the tube wall. My guess in your area would be ask Cycles DeOro who they'd recommend--I don't know what town they're in though.