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No matter what I do I can't get the rear derailleur adjusted

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No matter what I do I can't get the rear derailleur adjusted

Old 12-12-06, 11:25 PM
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BikeManDan
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No matter what I do I can't get the rear derailleur adjusted



Maybe I'm just not doing something right but I cannot for the life of me get this rear derailleur adjusted properly.

The setup I'm working with is an old Shimano 6 speed freewheel with an equally old Shimano triple up front. RD is a Shimano Alivio (8spd) and shifters are Shimano triggers (7spd).
Its a real mish mash of parts but correct me if I'm wrong, they should work together so long as it's tuned as a 6 speed system.

No matter how I adjust the barrel adjuster though, the shifts will only work on some gears and not others.
I've read that for Shimano indexed systems, you should adjust cable tension to get the 2nd smallest cog in perfect alignment and then supposedly all the others will work. This doesn't work in my case though.

It just seems like sometimes the shifters pull enough cable to shift to the next cog and sometimes they don't. And likewise sometimes enough cable is let back to shift down to another cog and sometimes not.


I have lubed all cable housings and thoroughly lubed all pivot points on the derailleur
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Old 12-12-06, 11:39 PM
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Is there another adjuster screw just behind the wheel drop out, that will move the top wheel on the derailer cage closer to the freewheel cogs? Some chains do have a lot of side to side play, and will just flex. But if the top wheel on the deralier cage is set closer to the hub it will then be 'forced' to move over rather than just flex.

You also need ... when adjusting the barrel screw to keep tightening it until the chain just begins to catch on the next ring up... then back it of a quarter of a turn. Then give it a try, it will shift up no problem, but it may not come down again.. so back it off a another quarter until it does.
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Old 12-13-06, 03:04 AM
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Originally Posted by dwoloz
The setup I'm working with is an old Shimano 6 speed freewheel with an equally old Shimano triple up front. RD is a Shimano Alivio (8spd) and shifters are Shimano triggers (7spd).
Its a real mish mash of parts but correct me if I'm wrong, they should work together so long as it's tuned as a 6 speed system.
You are wrong. 6 is not, never has been nor never will be a 7 speed. You need a 6 speed shifter or 7 speed freewheel. Then you will be surprised at how well it will work. Good luck

Tim
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Old 12-13-06, 03:37 AM
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Alright
Why does it matter though? Is the cog spacing different between a 6 and a 7? (I thought it wasn't)
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Old 12-13-06, 03:58 AM
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sometimes you can use one dérailleur and move up speeds but that's when they kept the same spacing and just crammed em in tighter if I'm not mistaken, but then again, I've never adjusted a dérailleur in my life.
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Old 12-13-06, 05:12 AM
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How's your derailleur hanger? On a bike that old I'd be surprised if it hasn't gotten bumped somewhere along the line. That'll definitely cause the kinds of problems that you are describing.

Try shifting into a gear that makes your derailleur arm hang straight down. Now walk around to the back of your bike and see if it hangs straight from that angle. If it looks a little bent in toward the wheel, clamp a big crescent wrench onto your derailleur and bend it back straight. Don't get tempted to remove your derailleur first or you might deform the mounting hole. You should be able to eyeball it straight enough for 6-speed.
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Old 12-13-06, 06:53 AM
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Originally Posted by dwoloz
Alright
Why does it matter though? Is the cog spacing different between a 6 and a 7? (I thought it wasn't)
Yes, the cog center to center spacing is different between Shimano 6,7,8 & 9 speed systems. The ones closest to each other are 7 & 8 speeds.
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Old 12-13-06, 08:48 AM
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Originally Posted by dwoloz
Alright
Why does it matter though? Is the cog spacing different between a 6 and a 7? (I thought it wasn't)
As noted, the cog spacing between 6 and 7-speed freewheels/cassettes is significantly different.

Several years ago, I bought a used '83 Trek 400 that the original owner had "upgraded" with a Shimano 6-speed freehub and 7-speed barcon shifters. He used the barcons in friction mode because, as he said, "the indexing never worked right". I got a new rear wheel that accepted a 7-speed freewheel and, wadda ya know, suddenly the indexing worked perfectly.
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Old 12-13-06, 10:49 AM
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According to Sheldon Brown's site, 6 speed spacing is 5.3mm cog center to cog center, 7 speed is 5.0mm.
http://www.sheldonbrown.com/k7.html Scroll down to the spacing chart.
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Old 12-13-06, 10:49 AM
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Originally Posted by HillRider
As noted, the cog spacing between 6 and 7-speed freewheels/cassettes is significantly different.

Several years ago, I bought a used '83 Trek 400 that the original owner had "upgraded" with a Shimano 6-speed freehub and 7-speed barcon shifters. He used the barcons in friction mode because, as he said, "the indexing never worked right". I got a new rear wheel that accepted a 7-speed freewheel and, wadda ya know, suddenly the indexing worked perfectly.
Amazing what happens when you follow the instructions. Wish I could get my 14 year old to accept that.

Tim
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Old 12-13-06, 12:48 PM
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Well I guess that explains that!
At least I know I'm not crazy and its the hardware, not me

Suppose I'm in the market for a 7 speed freewheel now if anyone has one
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Old 12-13-06, 01:54 PM
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I've heard good things about the new IRD freewheels. They are $40 from harris cyclery, and come in a few different ratios. You can also find shimano 7 speed freewheels for about $20.
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Old 12-13-06, 03:43 PM
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The Sheldon Brown website has instructions for alternate cable attachment at rear der to make a 8 sp shifter work with 7 sp sprocket. It worked for me. It may work for 7-6 mismatch.
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Old 12-13-06, 04:03 PM
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Sorry, mistaken post.
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Old 12-14-06, 02:28 PM
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This happened to me. I solved the problem by getting rid of the derailleur. You only need one.
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Old 12-14-06, 04:35 PM
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One thing you should check is the cable tension. Shift the chain to the smallest sprocket and see if there is slack in the cable. If there is, turn the barrel adjuster to one turn out from all the way in, and remove the cable slack at the clamp on the derailleur. Then you can start fine tuning the barrel adjusters. bk
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Old 12-14-06, 07:46 PM
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Originally Posted by bkaapcke
One thing you should check is the cable tension. Shift the chain to the smallest sprocket and see if there is slack in the cable. If there is, turn the barrel adjuster to one turn out from all the way in, and remove the cable slack at the clamp on the derailleur. Then you can start fine tuning the barrel adjusters. bk
When I first got the '83 Trek I mentioned above I tried everything you recommend to try to get at least useful , if not perfect, shifting over the 6-speed cassette with the 7-speed barcons. Trust me, nothing helped.
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Old 12-15-06, 12:02 AM
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Originally Posted by AndrewP
The Sheldon Brown website has instructions for alternate cable attachment at rear der to make a 8 sp shifter work with 7 sp sprocket. It worked for me. It may work for 7-6 mismatch.
+1
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