Maybe I have never payed attention or not cared enough to notice but.. Is it normal for an index shifter knob for rear gears to have a switch to change to friction? The two kinds of index knobs I have ever had(twist knob and rapidfire), I have not seen this on any of them. Nor do I remember ever seeing them on the button style thumb shifter like this one is. I simply slide the switch to the other side of the shifter and it becomes friction, slide it the other way index..


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Ahh, I miss the days when that was a standard feature on most MTB, and road shifters. If you wrecked your wheel at a race you could borrow anybodys wheel for the most part, even if it was a diferent drivetrain configuration, and make it work. I a really muddy race, if all else failed you could go to friction and still have some gears. What kind of shifter is it?
These are CLASSIC! NEVER get rid of these shifters!
Those are thumb shifters, not button, or trigger. they were made until around 1990, I think. Very hard to find clean examples. You may want to run them inverted (upside down). That's what we used to do. The biggest criticism back in the day was that if you had your palm on them (mainly the front) and hit a big bump, they could break your hand. Remember this was pre-suspention fork days. I don't know about the 6 speed ones, but later 7 speed ones had in extra, unmarked index spot that allowed them to be used on 8 speed systems. Back before Shimano had embraced the planned obsolescence strategy they now use. God I miss those things.
These are from the early, introductory period of index shifters. They were Shimano SIS (Shimano Indexing System) thumb shifters, and it was in the very beginning only the rear derailleur shifter that was indexed; the front was still friction. This would also coincide with the introduction of barrel adjusters on the derailleur. The rear could be switched back to friction in case the new system was too complicated or the adjustment got out of whack. Also if you switched wheels and cassette speeds. I had a very clean example of these until the bike fell over and snapped off the lever on the rear shifter. To answer your question, it was normal in the transitional period between friction and indexed shifting, which was brief. There were also once brake pad extenders in the early adoption of 700 c wheels over 27", but you would have a hard time finding these now.
It is normal on the Shimano thumb shifters of that era, as well as some other brands. I believe Suntour had that as well. Once thumb shifters were replaced by triggers, that feature disapeared forever on MTB's and only exists on bar-end and downtube shifters for road bikes now. On some old cheapo thumb shifters there was a d-ring on the top, like on the side of current swichable road shifters. It allowed you to go friction, but was often not clearly marked as such. Actually, I think thats how the old Suntour thumb shifters worked. It was common back in the day on decent bikes.

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