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Derailleur compatibility woes ?

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brendanheading Offline
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Posts: 3
Joined: Jun 2013
Post: #1
Derailleur compatibility woes ?
Hi guys,

I have a fairly long-in-the-tooth Dawes Giro bike, bought around 2000 or so. Over the years I've just replaced all the bits on it, so I've kind of become attached to it. It was, and still is, a 7-speed bike.

Back in around 2005, I got new wheels for it, and decided to replace most of the drive train but keeping it 7-speed (since the shifters are so damn expensive). I measured it and found 130mm clearance at the back so ordered the wheels with the then-current 8/9-speed 105 hubs. In order to keep the 7-speed cassette working correctly, a spacer has to be added on the freehub ahead of the cassette. Installed a SRAM PC95 chain, seems to work fine.

The bike was a bit worse for wear recently so I decided to spend a couple of quid and replace the cassette, chainrings, chain and derailleur. The derailleur is a new 105 jobbie, it's the long cage model (it was a real pain finding a new 7-speed cassette, I can tell you that much!).

The spacer arrangement with the cassette is as before but I just can't get the index adjustment to work right, despite hours of fiddling. On one hand, the all the sprockets shift fine, except I can't change out of the largest sprocket. If I slacken the cable slightly, just enough to allow it to shift, the cable is then too slack to pull the chain off the smallest sprocket when shifting up. The limit screws are correctly adjusted as far as I can tell.

Googling around, it appears that I may be hitting some sort of a compatibility issue. Back in the old days (groan) this sort of thing didn't happen, 7, 8 and 9 speed derailleurs from the same manufacturer just worked.

I guess my question is .. should I now solve this by going out and buying a set of 9-speed 105 shifters and installing a 9 speed cassette on the wheel ? (I know I can't do ten speed with this hub - but 9 should work). At this point I'm wondering if it's still worth keeping the bike going. A lot of love has gone into it so it's really painful to be in a position where I have to think about putting it on the scrapheap.
Jun 3, 2013 03:13 PM
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DaveM Offline
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Posts: 1,400
Joined: Aug 2008
Post: #2
RE: Derailleur compatibility woes ?
Sounds like you did everything right. At least in the US, 7 speed cassette are widely available, so it seems a little weird that you had trouble finding one. I think SRAM 7 and Shimano 7 are compatible. What kind of cassette did you end up with?

I'm also pretty sure that shimano 8/9/10 speed derailleurs should work with 7. But again, which exact derailleur did you get (model#)? Maybe it's something non-compatible with 7.

Check to make sure you got the cassette on right. Is the spacing between all the cogs exactly the same. Sometimes there are loose spacers on the outer cog and if that got left out, etc....

Finally, check to make sure derailleur hanger isn't bent. I've seen bikes where the hanger was bent, so someone bent the derailleur to compensate. Worked fine until you put on a new, straight derailleur and then the bent hanger messes it up.
Jun 4, 2013 02:23 AM
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brendanheading Offline
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Posts: 3
Joined: Jun 2013
Post: #3
RE: Derailleur compatibility woes ?
Thanks Dave.

Shimano do not seem to make 7-speed cassettes anymore, and by the sounds of things they haven't done for quite some time. There may be other manufacturers but I prefer not to complicate things by mixing them.

I've ridden the bike a bit more now and I'm finding that it's actually starting to improve. I've got it so that it shifts from the smallest cog all the way up to the largest smoothly. The only problem is that it is "hesitant" to shift from the largest cog to the second-largest. Whatever it is, it's very marginal and I'm thinking the issue may be to do with something snagging the gear cable. I reckon it's a matter of one or two millimetres somewhere and something is taking up that little bit of extra slack when the largest cog is selected.
Hmm, looking more closely I'm concerned that the outer cable next to the derailleur is absorbing some of the tension/slack when the derailleur is on the highest gear. I might try shortening it by a few inches.
Jun 4, 2013 01:37 PM
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DaveM Offline
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Posts: 1,400
Joined: Aug 2008
Post: #4
RE: Derailleur compatibility woes ?
I'm not sure if Shimano makes them or not, but there's 7 speed shimano branded cassettes all over Amazon. FYI. But if what you have is "shimano compatible" that shouldn't be the issue.

You might check if you have brake cable housing ("outer") instead of shifter housing. Brake housing can compress under tension which will mess up your shifting a little. Brake housing has a wire wound like a spring running through it, on shifter housing, the wires run parallel to the housing.
Jun 4, 2013 01:52 PM
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