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Old 07-30-05, 05:29 PM   #1
21delta
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Chain slack when coasting

I just got a new 18-speed. It's been a while since I've had a bike. I've noticed that when I stop pedalling my chain goes slack and the top part of the chain starts to rest on the lower part of the frame that connects to the rear wheels. As far as I can remember, this never happened on any bike I've had. What's causing this and how do I fix it?
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Old 07-30-05, 05:42 PM   #2
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Same here. My guess is I need more lube in the freewheel/freehub, because I've also noticed a gritty/grindy sound/feel when the rear wheel spins.
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Old 07-30-05, 05:57 PM   #3
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I've noticed that when pedalling and then coasting that the arm under the derailleur (not sure what it's called) swings forward, causing the chain to go slack. Here is a picture of that part while the chain is taut. Does that appear to be the correct angle for it?

http://scottaponte.com/gallery/albums/album10/bike.jpg
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Old 07-30-05, 07:08 PM   #4
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If it happens only in high gear when you stop pedalling abruptly, it's likely normal.

Otherwise, it might be related to a quite few factors :

- too long chain (if it happened from day one) ;
- very dirty chain ;
- very dirty, gummy and therefore lazy derailleur springs.

As for your derailleur, it's position seems OK, but I am not so sure about its angle because I don't see the front end. Normally, when your chain is sitting on your largest chainring and largest cog, the derailleur should be very tight (i.e. horizontal, with the lower pully forward). So tight, in fact that if you pull strongly on the chain, you might have 1, maybe 2 links "too many". I suspect that you have 6-7 of them, which makes the derailleur under-tensioned.
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Old 07-30-05, 07:44 PM   #5
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Quote:
Originally Posted by 21delta
I've noticed that when pedalling and then coasting that the arm under the derailleur (not sure what it's called) swings forward, causing the chain to go slack.
In your picture it looks good. The derailleur arm prevents slack, not causes it. The arm is pulling forward because the cassette is rotating with the wheel when you coast, tensioning up the bottom stretch of chain and creating slack on the top stretch of chain. At least that's what it sounds like. You could also get lots of slack if you had too many links on the chain, so that the derailleur arm can't keep tenison anywhere when using the small rings/cogs.

WRT the above post, I'm don't know how a dirty chain would cause what you describe.
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Old 07-31-05, 12:36 PM   #6
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Quote:
Originally Posted by Michel Gagnon
If it happens only in high gear when you stop pedalling abruptly, it's likely normal.

Otherwise, it might be related to a quite few factors :

- too long chain (if it happened from day one) ;
- very dirty chain ;
- very dirty, gummy and therefore lazy derailleur springs.

As for your derailleur, it's position seems OK, but I am not so sure about its angle because I don't see the front end. Normally, when your chain is sitting on your largest chainring and largest cog, the derailleur should be very tight (i.e. horizontal, with the lower pully forward). So tight, in fact that if you pull strongly on the chain, you might have 1, maybe 2 links "too many". I suspect that you have 6-7 of them, which makes the derailleur under-tensioned.
The bike is brand new so the chain isn't dirty or gummy. How would I know if I had too long of a chain? The bike came pre-assembeled so as far as I know, the chain is exactly as it was out of the box.

I also just noticed that if I move the pedals in the opposite of the normal direction (pedal backwards) the rear wheel starts to go backwards. Maybe things have changed with bikes, but that doesn't seem normal to me.

Last edited by 21delta; 07-31-05 at 02:08 PM.
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Old 07-31-05, 08:16 PM   #7
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Quote:
Originally Posted by 21delta
The bike is brand new so the chain isn't dirty or gummy. How would I know if I had too long of a chain? The bike came pre-assembeled so as far as I know, the chain is exactly as it was out of the box.

I also just noticed that if I move the pedals in the opposite of the normal direction (pedal backwards) the rear wheel starts to go backwards. Maybe things have changed with bikes, but that doesn't seem normal to me.
Then maybe the chain is too long. Some bike manufacturers supply a standard Shimano or Sram chain (114 links, I think) rather than a chain cut the proper length. It probably is a bit cheaper for the manufacturer, but it also allows the bike shop to fiddle with the ideal cogs and rings (depending on model, customer requests...). The shop mechanic is supposed to cut the chain to its proper length according to your actual gearing, but I'm aware that many don't do it.

If you want an illustration of the proper chain length, see http://parktool.com/repair_help/FAQchainlength.shtml

There could also be a problem with the B-screw of the derailleur (the one near the top that gives it its angle), or with a defective spring in the derailleur.


As for the wheel going backwards, if it happens when the bike is up and if it is a slow movement which is very easy to stop with your hand, then it is normal. It simply means that your rear hub is still new and offers next to no friction. As you cycle, this "problem" will solve itself automatically when your bearings will get dirty.
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Old 07-31-05, 09:03 PM   #8
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I was looking at it today and I noticed the cassette (that's the group of gears on the rear wheel, right?) turns with the rear wheel any time it's moving. I called a bike shop and they told me it's not supposed to do that. Is that correct? In any event, I contacted the store I bought the bike from and they were out of stock on that model and said their manager would call me tomorrow to tell me what they can do for me. So I guess I won't fiddle with it too much.
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Old 08-01-05, 01:43 AM   #9
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Freehub isn't actually free at all sounds like. That would definitely cause your problem.

Yes the group of cogs is a cassette.

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Old 08-01-05, 12:47 PM   #10
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Quote:
Originally Posted by 21delta
The bike is brand new so the chain isn't dirty or gummy. How would I know if I had too long of a chain? The bike came pre-assembeled so as far as I know, the chain is exactly as it was out of the box.

I also just noticed that if I move the pedals in the opposite of the normal direction (pedal backwards) the rear wheel starts to go backwards. Maybe things have changed with bikes, but that doesn't seem normal to me.
LOL!!
Buying bikes in boxes is great for those with the mech. knowledge to handle issues such as you've encountered.
For the rest of us, a trip to the LBS will be required, either to purchase the bike or to have our mail order bike tuned up.
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