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I have a bike with downtube friction shifters and a 5 speed freewheel. When I bought the bike a while ago the shifters weren't connected so I did it myself. At this point it all worked fine. I took it to the local bike shop to check out what I had done, as I had never done it before. He did some adjustments (I don't know exactly what) and ever since I have had trouble with getting the lowest gear (biggest cog) and the derailleur shifts automatically back down to the smallest cog.

I have checked:

  • the cable - it is tight
  • the limit screws - they are fine
  • the shifter - even when tightened I have the same problem

Today I notice three things:

  • the cable binder bolt on the rear derailleur is loose, so it spins on its attachment to the derailleur. I assume this is a problem.
  • the cable is frayed after only a couple of months use
  • in order to move gears I have to put a huge amount of pressure on the shifter and it only uses about one third of the possible span of movement. When I set it up in the first place the lowest gear and highest gear were almost 180 degrees apart on the lever (if that makes sense).

I now need to replace the cable but how can I fix the derailleur issue? Does it just need replacing? I put a photo showing the position of the derailleur in 1st gear to check if the chain is the correct length.

I don't really want to go to the bike shop again as he isn't the friendliest person....

Many thanks for your help. Gill

enter image description here

enter image description here

enter image description here! This is the shifter position when it is on the big cog. enter image description here

  • I edited you question to clarify which gear you are referring to. The largest cog is known as the lowest, first gear; not the highest fifth, gear. – Argenti Apparatus Jul 20 at 13:22
  • Thank you for doing that. – Gill Jul 20 at 14:08
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We know it worked once, but we don't know what was changed, so it's time to go back to basics.

Auto shifting
The rear derailleur has a spring that wants to move the chain to the smallest cog.
The shift lever should have enough friction to keep the derailleur spring from going where it wants but not be so tight that it won't move.

The first thing to check is that the wing nut is tight.
If the wing nut is tight and there is still auto shifting then it's time to check how the levers for correct assembly.

My guess is that you have shift levers that look something like this:
enter image description here
Check that all the washers are there and in the right place.

Low gear
There are at least three main things that can keep you from getting low gear.

  1. Limit screws - you have checked them and they are fine. Just to make sure, can you move the derailleur by hand and get the chain to go into low gear? If so then we know it's not the limit screws.
  2. Cable tension - with the chain in the smallest cog and the shift lever all the way down the cable should have no slack.
  3. Derailleur alignment - here's a picture:
    enter image description here
    Picture from SOS Hanger
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  • I have a poor man's version of that. There is no wing nut, just a screw, which is annoying. I haven't taken it off to check the washers but I will when I change the cable. I have a spare shifter as well that I could try. I can move the derailleur by hand to the largest cog but it is true that the chain does not run smoothly on that cog no matter where I hold the derailleur. Maybe I should check the teeth. I checked the alignment and it looks OK. Even by hand it requires a lot of force to push the derailleur in. – Gill Jul 20 at 14:15
  • I just put it back together, went for a slow ride with it on the big cog and it hasn't moved yet. But I know if I were to put pressure on the pedals by going uphill it would shift. – Gill Jul 20 at 14:16
  • What kind of bike is that? When I find shift levers like yours they have an adjusting barrel where yours does not. If I can find a picture of your bike when new we can see if yours is original. – David D Jul 20 at 16:01
  • Thank you! It is a bike from a French maker called Simon (or SIC I think) in Troyes. It was made in 1984 I think. I will try and add a photo. – Gill Jul 20 at 16:56
  • @Gill That is a lovely bike. Looking at the picture the cable routing does look correct. I could find no exact match anywhere for your bike. – David D Jul 20 at 18:56
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Sounds like the cable is pulling through the binder bolt on the derailleur, so that the shifter cannot pull the derailleur inboard onto the largest sprocket.

The shifter cable needs replacing. Check that the housing is properly located in all the frame stops. It would be good to put a ferrule on the end of the shift cable also.

It's possible that the derailleur lower limit screw is set to high and is preventing the derailleur moving inboard enough to engage the largest sprocket properly. You can check this by manually pedaling and carefully pushing the derailleur towards the largest sprocket.

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  • Thank you. I will replace the cable. I will try again to fit a ferrule - it was too tight and the bike shop told me I didn't need one. I tightened the bolt and it is slightly better. – Gill Jul 20 at 14:19

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