Bicycle Mechanics - Chain/Freehub Problems
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11-15-07, 07:40 PM
Recently a problem developed with my Raleigh M20 mountain bike. When ever the front is on the second chain ring and first cog in the back if I pedal backwards the chain jumps to the second cog. This is an annoying problem that I can't figure out. When ever the front chain ring is on the smallest it doesn't jump. Also it has a 7sp Shimano mega range rear free hub and a triple chain ring up front. I tried adjusting both derailluers with no improvement. I'm thinking either the chain or free hub is worn. What do you guys think? Thanks
11-15-07, 08:10 PM
The drivetrain isn't meant to go backwards, but...
It is usually caused by an angled chain. May not be anything wrong with your setup but try this: Make sure the low limit screw on the rear derailleur isn't too tight (but not so loose that the chain falls into the spokes).
11-16-07, 02:09 PM
I tried adjusting the low limit screw and it didn't help. I think the chain is worn out, and also it never did this until a few days ago. The chain is only $7 so I think I'll try a new one.
11-17-07, 09:48 AM
There may or may not be a solution to your "problem".
The may-be solution:
Park the bike and look carefully at your chain when you backpedal. Does it fall down from largest to second largest cog when the cog is always in the same spot? A good place for the fall would be at one of the ramps used to help the chain go up when you shift. If that's the case, it's most likely normal, as the end of the ramp will also help the chain to shift down when you backpedal. That unfortunate turn of even happens especially when the chain is very oblique, which is why it happens mostly on the outside rings.
But here is another catch: look carefully at the offending cog and check for straightness. Large 8- and 9-speed cogs are fairly easily bent, and a crooked cog will allow the chain to fall down. If that's the case, you have two options:
– accept the problem and learn NOT to backpedal;
– change the offending cog or the whole cassette. If you do so, you should also replace the chain, unless it's a very new one.
BTW, as it happens when you backpedal, the derailleur has nothing to do with it. The derailleur allows you to shift (by moving right and left) and helps to keep the chain in check (by being aligned with the cog) as long as you pedal forward. But when you pedal backwards, the chain isn't guided by the derailleur.
11-18-07, 06:23 PM
Bent derailleur hanger?
11-18-07, 06:32 PM
I checked and the largest cog is ever so slightly bent. I'll just live with it because I never pedal backwards when I ride anyways.
11-21-07, 09:20 PM
You nailed the problem. It's fairly easy to learn to live with.
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