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I have friction shifters and for some reason the front one gives me a bit of trouble. It tends to return to its most untensioned state. So say I want to shift to a higher gear, it will try to drop me back down to my lower gear. My guess is I might need to lube up the cable and shifter. Any other known solutions?

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Could you please include some more info about the shifter? Make and model? A picture? –  freiheit Sep 28 '11 at 17:11
    
It is a Sun Tour shifter on my headset. –  anton2g Sep 28 '11 at 17:24
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You should edit that information into the question. The specific model or a picture would still also be useful, since I'm pretty sure Sun Tour has made more than one model of friction shifter. –  freiheit Sep 28 '11 at 17:31
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Have you tried simply tightening the tension screw? I believe on the standard SunTour it's a little thumb screw that folds out so you can twist it. –  Daniel R Hicks Sep 28 '11 at 23:05
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2 Answers

up vote 9 down vote accepted

With friction shifters this is usually caused by one of two problems:

  • Loose Shifter Screw: Friction shift levers usually have a wing-nut-screew used to adjust the tension and friction of the lever against the mounting housing. Tighten this screw, but not too tight or else you can't move the shift lever. You can also take the shifter apart (noting carefully the order of the parts) and clean everything with degreaser. DO NOT LUBE - you are trying to regain friction, not remove it.

Edit re. ʍǝɥʇɐɯ - After you adjust everything you may find that the shifter screw continues to come loose almost immediately - in that case you may want to use a little 'adjustable/removable' Loctite on the screw, assemble, and let it sit for a while before using. That should help hold everything together.

  • Cable Friction: Often there will be one or more points of friction on the cable route. This could be in the housing, or in the routing channels under the bottom bracket. As you apply pressure to the pedals the frame flexes, pulling the cable one way, but then the friction stops it from sliding back. Check and clean your housings and routing points, especially at the bottom bracket.
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The problem is the friction on the screw rather than the friction on the lever. More friction is needed on the screw (with some blue stuff dabbed on there) so it behaves more like a ny-lock nut/bolt combo. Since it is already with enough derailleur spring coming through (for the lever to slip) there is no need to attend to the cable or to clean/degrease the lever, that friction level is set by the screw, however there is not enough friction on this screw's thread. –  ʍǝɥʇɐɯ Sep 29 '11 at 0:09
    
How do you know the screw is coming loose? The OP never said anything about tightening it. And simply operating the shift lever does not transfer torque to the screw unless a component has been broken or left out. –  Daniel R Hicks Sep 29 '11 at 15:33
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I thought you might want to know the historical background to this particular problem and how to fix it so that it stays fixed...

Suntour 'Power Ratchet' friction shifters contain a spring and a ratchet, with the ratchet working one way, the idea being that it should be easy to shift gears with them. On most of their shifters of this era, e.g. the down tube, top-shifter and bar-end variants, there was a ratchet in both levers. However, with the stem-mounted shifters (as commonly found on more affordable bikes) they skimped on the ratchet for the left hand lever.

Here is a diagram for a down-tube lever, note the two ratchets (10):

enter image description here

Now here is what you have, note how parts (10) and (11) only feature on one side:

enter image description here

So the lever set is 'defective' from the start, no little ratchet like you have on the right lever. The consequence of this is that the lever is always trying to undo the screw. Plus, even if you do not actually use the gear, there is the small matter of road vibration, this too loosens the screw.

To remedy this problem you need to increase the friction on the screw (17), not the lever gubbins as a whole. Place a small dollop of Loctite on the screw thread, do up the screw to how it suits you and the job should be a good one.

Hope that helps!

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I wouldn't advise the Loctite, unless you're careful to use the "adjustable" variety. Certainly one should not use the standard "non-removable" variety. –  Daniel R Hicks Sep 28 '11 at 23:07
    
...what's the small blue dot on normal down-tube shifter bolts? It is 'a Loctite-style product', vibra-tite.com/vc3.html is another, 'friction through viscosity' rather than 'glue'. It will do the job, even on those cheap Shimano plastic top-bar thumbshifters. –  ʍǝɥʇɐɯ Sep 28 '11 at 23:54
    
There are, last I checked, four varieties of regular Loctite. The most common is the "permanent/non-removable" variety. It is effectively a glue. Stronger even than that is "stud" Loctite, which will only come loose if the joint is heated to a fairly high temperature. The other two varieties are "removable" and "adjustable". If one uses the "removable" variety it will hold until you adjust it a few times and then lose its grip. The "adjustable" variety will survive a few dozen "adjustments", perhaps. –  Daniel R Hicks Sep 29 '11 at 1:08
    
And I'm not quite sure why you say these levers are "defective". Shifters were made this way -- utilizing only friction -- for decades -- pretty much since derailers became available. And they worked well for decades. Certainly improvements are possible (and have been made) but there's nothing wrong with the old stuff. –  Daniel R Hicks Sep 29 '11 at 1:11
    
This is certainly informative and very interesting. I was able to fix the problem by tightening the screw. It should last a while, and seems like an easier solution to keep doing that, then to disassemble the whole deal. But still very interesting piece, which I knew more stuff like this. –  anton2g Sep 29 '11 at 14:45
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