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I've finished a bike restoration today and it's my first time using downtube shifters. They work and will span the full range of gears but won't stay in the big cog on the back for long, the shifter itself gets pulled down by the cable tension, I've tried loosening the cable but I'm just not sure how to set it up. Which gear should the bike be in, what position should the shifter be in and how tight do I pull the cable? I've tried tightening the actual shifter against the frame, that didn't help. It was a little D ring that pulls out, it's pretty stubborn so I grabbed it with pliers and managed to bend it off, ghetto repaired for now. I'm assuming it's cable tension.

The H and L screws are ok, I'll try disassembling it if I can find a diagram for my shifter.

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    The thing you broke off is used to adjust the friction in the shifter. If there's not enough friction in the shifter then it slips and the cable becomes looser, causing a gear change. – Daniel R Hicks Jun 9 '18 at 22:51
  • It's not broken I managed to get it back, just a bit bent. I had it as tight as possible yet it still slipped. – Harvey Brackenbury Jun 9 '18 at 22:54
  • The D ring switches between index and friction shifting, and doesn't tighten the shifter against the frame. The friction adjuster is normally a screw. – Batman Jun 9 '18 at 23:22
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    The bike is pre indexed shirting, the d ring pivots out and tightens the shifter or loosens it for sure because if I keep turning it left the shifter comes off. There's no indexed mode on any of the parts or the shifters. – Harvey Brackenbury Jun 9 '18 at 23:29
  • Is the shifter itself slipping? If so, and if the friction setting is as tight as possible, likely the shifter has been disassembled some time in the past and reassembled incorrectly. But if the shifter isn't slipping then your problem is most likely on the other end, with the high and low screw adjustments. Try easing off on the L screw a couple of turns. – Daniel R Hicks Jun 9 '18 at 23:56
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Downtube shifters are usually called "friction shifters" and friction is key when fixing the issue you describe. I own and periodically use an old Cannondale with such system. Every now and then I find myself with the same problem as yours. How to fix it? Easy, just tighten the lever of the shifter.

Mine came with an integrated metal triangle handle (couldn't find its exact name, but I've attached a picture as an example.) So they can be tightened using your bare fingers and on the fly, but some other models might need to use a screwdriver. The H and L limits of the derailleurs will have nothing to do with this problem.

enter image description here

  • However, if the H or L screw on the derailer is too far advanced then you will generally have difficulty keeping the derailer in the highest or lowest gear. – Daniel R Hicks Jun 10 '18 at 20:14
  • @DanielRHicks Right. Generally you will not be able to jump into such gear but if the H/L screw adjustment happens to fall just in the middle of a hear jump, that would definitely cause such kind of problem. – Lementor Jun 10 '18 at 20:16

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