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Old 10-18-09, 06:15 PM   #1
rekall
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8 speed shifter + 7 speed cassette?

friend of mine has an old back wheel that recently became un-rideable. 24-speed raleigh with shimano grip shifters, so, 8 speeds on the right shifter. and also recently i upgraded my rear wheel to a 7 speed freehub, so i've got a spare 7-speed freewheel cassette wheel i could 'let go' in the interest of getting him back in action without spending a dime... is it possible for an 8 speed shifter to reliably operate a 7 speed cassette? (cassette is also a shimano.)
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Old 10-18-09, 06:44 PM   #2
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Some people have tried this and been satisfied, personally I was never satisfied with the indexing.
The spacing difference between 7 speed and 8 is only 0.2mm per cog but I could not get it set up to work well.
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Old 10-18-09, 06:52 PM   #3
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Some people have tried this and been satisfied, personally I was never satisfied with the indexing.
The spacing difference between 7 speed and 8 is only 0.2mm per cog but I could not get it set up to work well.
That's been my personal experience too.

I've messed with various combinations of 7 and 8 speed shifters and cassettes over the years. I can get it to "kind of work" but I've never been able to get it to index to my satisfaction over an extended period.
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Old 10-18-09, 07:42 PM   #4
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8 will not shift 7 properly.
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Old 10-18-09, 10:56 PM   #5
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I've done it with grip-shift and it worked well enough for me.
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Old 10-18-09, 11:15 PM   #6
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Replace the 7-speed spacers with 8-speed spacers (Your local LBS probably has a bunch in a junk box), if* both are cassettes (You mentioned cassettes & freewheels when describing the problem; ensure the lock-ring tightens down (If not add a thin spacer); re-adjust the rear derailleur's limit screw(s), and your friend's in business. Good luck!

*If not, just try it the way it is and see if he can live with the sloppiness.
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Old 10-19-09, 01:36 AM   #7
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I've gotten 8-spd shifters to work with 7-spd clusters by using Sheldon Brown's alternate cable routing method. By bolting the cable differently, you make the derailleur move more for the same cable-pull. Originally this was a way to get around incompatible cable-pulls of the Dura-Ace system, but it also works with other shifters as well.
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Old 10-19-09, 04:56 AM   #8
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so i just undo the cable at the RD and kink it at a right angle and retighten? easy enough to try and see!
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Old 10-19-09, 06:19 AM   #9
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so i just undo the cable at the RD and kink it at a right angle and retighten? easy enough to try and see!
Yes, you clamp it in front of the bolt instead of behind.

Even though 0.2mm spacing difference between sprockets don't seem like much, across 7 of them, you're off by 1.4mm, which is significant. So if you adjust cable-tension to centre the derailleur under the 1st sprocket precisely, by the time you've shifted to the 7th one, it's off by 1.4mm. The effect is shifting gets worse and worse as you move across the cluster. The alternate cable-routing makes up for that difference by changing the pivot-distance between the cable-housing stop and the cable-clamp bolt so the derailleur moves more per click.
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Old 10-19-09, 07:10 AM   #10
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Yes, you clamp it in front of the bolt instead of behind.

Even though 0.2mm spacing difference between sprockets don't seem like much, across 7 of them, you're off by 1.4mm, which is significant. So if you adjust cable-tension to centre the derailleur under the 1st sprocket precisely, by the time you've shifted to the 7th one, it's off by 1.4mm. The effect is shifting gets worse and worse as you move across the cluster. The alternate cable-routing makes up for that difference by changing the pivot-distance between the cable-housing stop and the cable-clamp bolt so the derailleur moves more per click.
If you're trying to get some mis-match combination to work, centering the rear derailleur at one end and hoping it will work across the range is the worst practice. The best arrangement is to set the shifter to the center of the range and a center the derailleur to the corresponding cog with the cable tension so the spacing error is evened out across the cassette, but even doing this does not get shifting performance to my satisfaction with the arrangement the OP is proposing.
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Old 10-19-09, 03:19 PM   #11
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Shimano Ultegra 8 Speed Bar-end Shifters LD801 $84.95
These permit switching between indexed and friction shifting.
Complete with cables, housing and down-tube cable stops for attachment to down-tube braze-ons. If your bike doesn't have the braze-ons, you also need to buy a pair of clamp-on cable stops.

The 7-speed units are no longer available, but the 8-speed shifters actually work quite well with 7-speed cassettes, especially with modern rear derailers.

It works for me and a lot of other people.
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Old 10-20-09, 12:23 AM   #12
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Shimano Ultegra 8 Speed Bar-end Shifters LD801 $84.95
These permit switching between indexed and friction shifting.
Complete with cables, housing and down-tube cable stops for attachment to down-tube braze-ons. If your bike doesn't have the braze-ons, you also need to buy a pair of clamp-on cable stops.

The 7-speed units are no longer available, but the 8-speed shifters actually work quite well with 7-speed cassettes, especially with modern rear derailers.

It works for me and a lot of other people.
Will it work with older deraillers from he 80s or early 90s for those of us who have more vintage drivetrains and want to get some bar-end shifters for our 7-speed rides?
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Old 10-20-09, 03:13 AM   #13
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Only on non-Dura-Ace Shimano indexing derailleurs.
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Old 10-20-09, 05:24 AM   #14
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By "modern rear derailers" they mean derailers with a floating jockey pulley (Centeron).
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Old 10-20-09, 05:29 AM   #15
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If the OP`s friend has grip shifters currently, I doubt he`d be able to mount barends.
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Old 10-20-09, 07:58 AM   #16
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The type of shifter makes no difference. The cable pull is the same.
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Old 10-20-09, 08:13 AM   #17
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The type of shifter makes no difference. The cable pull is the same.
For indexing purposes you are correct, however Gripshifts imply a mountain bike bar with a smaller diameter than road bars so bar-ends will not fit into them as they are made for road bar diameter.
Of course, if the Gripshifts in question are of the SRAM X series than the cable pull will be different.
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Old 10-20-09, 09:48 AM   #18
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Originally Posted by DannoXYZ View Post
Yes, you clamp it in front of the bolt instead of behind.

Even though 0.2mm spacing difference between sprockets don't seem like much, across 7 of them, you're off by 1.4mm, which is significant. So if you adjust cable-tension to centre the derailleur under the 1st sprocket precisely, by the time you've shifted to the 7th one, it's off by 1.4mm. The effect is shifting gets worse and worse as you move across the cluster. The alternate cable-routing makes up for that difference by changing the pivot-distance between the cable-housing stop and the cable-clamp bolt so the derailleur moves more per click.
Even in the case that you adjust the shifter to be perfect on the end cog, it will only be 1.2 mm off- there are only 6 steps between the first and last cog of a seven-speed cog. But if you adjust it to be correct in the center, it will only be .6mm off at the ends- that's only 3 steps from the middle to each end.

But, if you use Sheldon's alternative routing of the cable, the shift steps will be 5.3 mm rather than 4.8 mm, which will have .3mm/step error, and .9mm error at each end of the cassette. This may work better because it tends to make the shift easier (but tends to make double shifts easier, too). A good rear mech should be used in either case.

Last edited by cycle_maven; 10-20-09 at 09:56 AM.
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Old 10-20-09, 07:40 PM   #19
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Use 8 speed spacers and it should work well enough.
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Old 10-20-09, 08:31 PM   #20
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Originally Posted by Dirtdrop View Post
Shimano Ultegra 8 Speed Bar-end Shifters LD801 $84.95
These permit switching between indexed and friction shifting.
Complete with cables, housing and down-tube cable stops for attachment to down-tube braze-ons. If your bike doesn't have the braze-ons, you also need to buy a pair of clamp-on cable stops.

The 7-speed units are no longer available, but the 8-speed shifters actually work quite well with 7-speed cassettes, especially with modern rear derailers.

It works for me and a lot of other people.
Wrong

8 shifters isn't going to do 7, end of story.
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Old 10-20-09, 09:14 PM   #21
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Wrong

8 shifters isn't going to do 7, end of story.
Despite the evidence to the contrary by hundreds of riders who are using 8 speed shifters with 7 speed cassettes/freewheels right now
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Old 10-20-09, 11:07 PM   #22
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Anything anecdotal on using Mavic 821 shifters (downtube 8-speed indexed) shifters to work with a 7 speed freewheel?

I've got a bike with 126mm rear spacing (aluminum frame). I really want to run Mavic 8 speed on this bike.
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Old 10-21-09, 09:31 AM   #23
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Anything anecdotal on using Mavic 821 shifters (downtube 8-speed indexed) shifters to work with a 7 speed freewheel?

I've got a bike with 126mm rear spacing (aluminum frame). I really want to run Mavic 8 speed on this bike.
This is exactly what I am running on my utility road bike. Mavic 8 speed downtube indexing (821 sounds right) shift levers, and a 7 speed Shimano 105 126mm hub with a 7 speed Uniglide cassette. Will it work? Short answer: "yes it will". Long answer: not exactly perfectly, but good enough. Its good that Shimano indexing rear derailleurs have that "Centeron" upper pulley, because the slight mismatch of the pull of the shift lever to the spacing of the 7 speed cluster culminates in the last (biggest) cog in the back not shifting on the last click, you end up needing the extra (8th cog) click to make it. Hope this makes sense. One nice thing about the Mavic levers though, I believe the clicks are not hard stops per se, they seem to have some extra wiggle room on each gear setting that lets you fine tune your gear choice just a little bit.
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Old 10-21-09, 05:32 PM   #24
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I was just running through the gears on the stand and I don't see any significant misalignment at either end. It runs quiet, too. I'm using a Shimano Hyperglide 7 speed 13/28 cassette, Shimano 8 speed bar end shifters and a Shimano 600 Tricolor RD. The cable is run normally. It hasn't missed a shift in the three years I've been running this setup.
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Old 10-21-09, 07:09 PM   #25
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Wrong

8 shifters isn't going to do 7, end of story.
You're always so adamant about things you've obviously never tried. Like Dirtdrop I've got a bike that is working just fine with an XT integrated 8 speed brake/shifter running a Deore long cage and an old 7 speed cassette. It's not as smooth as my fully 8 speed systems and takes a bit more fussing to tune it but it works across the entire range of seven speeds with no need for cable trimming for months and months at a time.
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