Using 7s indexed DT shifters on an 8s cassette
04-30-13, 06:25 PM
#1
Tyrannosaurus Rexitis
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Using 7s indexed DT shifters on an 8s cassette
Hey guys, long time, no post with a problem.
I'm trying to figure this one out. My new bike has 7s Shimano 600 Tricolor shifters but my rear end is 8s. When I stand in the biggest cog it shifts down to the second biggest due to frame flex.
I know, I know, try it in friction mode. But I'm spoiled and like indexing for DTs. Any suggestions for getting this to work or am I outta luck? Suppose I should hit up the trade thread.
Dramatic pic of bike in question:
I'm trying to figure this one out. My new bike has 7s Shimano 600 Tricolor shifters but my rear end is 8s. When I stand in the biggest cog it shifts down to the second biggest due to frame flex.
I know, I know, try it in friction mode. But I'm spoiled and like indexing for DTs. Any suggestions for getting this to work or am I outta luck? Suppose I should hit up the trade thread.
Dramatic pic of bike in question:
04-30-13, 06:36 PM
#2
Senior Member
They made 8 speed indexed shifters and they're likely on ebay or elsewhere, that'd be the easiest solution, really.
04-30-13, 07:43 PM
#3
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Sun Race makes an eight speed indexed Downtube shifter that plays nice with Shimano eight speed cassette and derailleur. Remarkably cheap, too.
04-30-13, 09:43 PM
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04-30-13, 10:42 PM
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I like the cool paint on the frame. Can we get a nice shot of the paint job??
04-30-13, 11:32 PM
#6
Velocommuter Commando
Hey guys, long time, no post with a problem.
I'm trying to figure this one out. My new bike has 7s Shimano 600 Tricolor shifters but my rear end is 8s. When I stand in the biggest cog it shifts down to the second biggest due to frame flex.
I know, I know, try it in friction mode. But I'm spoiled and like indexing for DTs. Any suggestions for getting this to work or am I outta luck? Suppose I should hit up the trade thread.
Dramatic pic of bike in question:
I'm trying to figure this one out. My new bike has 7s Shimano 600 Tricolor shifters but my rear end is 8s. When I stand in the biggest cog it shifts down to the second biggest due to frame flex.
I know, I know, try it in friction mode. But I'm spoiled and like indexing for DTs. Any suggestions for getting this to work or am I outta luck? Suppose I should hit up the trade thread.
Dramatic pic of bike in question:
https://www.ebay.com/itm/Vintage-shif...item2ec7cb5809
These are Shimano 600 NOS:
https://www.ebay.com/itm/New-Old-Stoc...item3f249ace13
None of these are my auctions just trying to help..
05-01-13, 01:51 AM
#8
Full Member
you could try tightening the cable a hair and loosening the limit screw for the big cog a touch to see if it will be enough.
05-01-13, 04:41 AM
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Often, when you mismatch the indexed shifters and cogs things will appear to play well together over the majority of the cogs, This is the Centeron pulley doing it's job and accommodating he mismatch in cable pull and cog spacing. However, when you get to extremes of the cog range, the mismatch becomes too great and things get noisy, ghost shift or just won't make the shift.
05-01-13, 05:44 AM
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What about a 7 speed cassette? It and a spacer behind it will match the cassette with the current shifters. I have a lightly used 7 speed Shimano and/or SRAM cassette(s) you are welcome to try.
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05-01-13, 08:00 AM
#12
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T-Mar has it with the 1.4 mm spacing issue. See Sheldon's cribsheet here. For this to work, you need to set it up *precisely* in the 5th cog on the rear. Your offset going to the largest cog is then 3 x 0.2 = 0.6 mm, which isn't too bad. Going the other way, the offset is 0.8 to the smallest cog. Why the 5th and not the 4th? Either could work, but in general your RD will drop into the smallest cog more easily than it will climb to the largest cog.
If it were me, I'd follow Bob's advice and probably change the cassette to a 7-speed because these are only $15-$20 new. If I couldn't do that, I'd follow Robbie's advice and switch to 8s shifters. I've done enough cross-matching of Shimano components (6s/7s/8s/and 9s) to know that it can become a PITA, but that it can also work flawlessly.
If it were me, I'd follow Bob's advice and probably change the cassette to a 7-speed because these are only $15-$20 new. If I couldn't do that, I'd follow Robbie's advice and switch to 8s shifters. I've done enough cross-matching of Shimano components (6s/7s/8s/and 9s) to know that it can become a PITA, but that it can also work flawlessly.
05-01-13, 08:27 AM
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To my thinking, it's kind of a shame to waste 130mm spacing with a 3.5mm shim behind the cassette just to make the right shifter work. You should be able to pick up nice used shifters (or just the right one, aren't 7- and 8-speed 600 a cosmetic match?) for much cheaper than those NOS examples.
05-01-13, 04:43 PM
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https://www.bikeforums.net/showthread...=#post15567400
Almost certainly. Seven speed and eight speed cog spacing are different by about 0.2mm. That's not much but over 7 cogs it adds up to 1.4mm. It eventually gets to the point where the Centeron pulley does not have enough lateral travel to center the chain with the cog. In your case, the relative misalignment is not enough to prevent what appears to be a good shift but once pressure is applied to the pedals you get the get ghost shift.
Often, when you mismatch the indexed shifters and cogs things will appear to play well together over the majority of the cogs, This is the Centeron pulley doing it's job and accommodating he mismatch in cable pull and cog spacing. However, when you get to extremes of the cog range, the mismatch becomes too great and things get noisy, ghost shift or just won't make the shift.
Often, when you mismatch the indexed shifters and cogs things will appear to play well together over the majority of the cogs, This is the Centeron pulley doing it's job and accommodating he mismatch in cable pull and cog spacing. However, when you get to extremes of the cog range, the mismatch becomes too great and things get noisy, ghost shift or just won't make the shift.
T-Mar has it with the 1.4 mm spacing issue. See Sheldon's cribsheet here. For this to work, you need to set it up *precisely* in the 5th cog on the rear. Your offset going to the largest cog is then 3 x 0.2 = 0.6 mm, which isn't too bad. Going the other way, the offset is 0.8 to the smallest cog. Why the 5th and not the 4th? Either could work, but in general your RD will drop into the smallest cog more easily than it will climb to the largest cog.
If it were me, I'd follow Bob's advice and probably change the cassette to a 7-speed because these are only $15-$20 new. If I couldn't do that, I'd follow Robbie's advice and switch to 8s shifters. I've done enough cross-matching of Shimano components (6s/7s/8s/and 9s) to know that it can become a PITA, but that it can also work flawlessly.
If it were me, I'd follow Bob's advice and probably change the cassette to a 7-speed because these are only $15-$20 new. If I couldn't do that, I'd follow Robbie's advice and switch to 8s shifters. I've done enough cross-matching of Shimano components (6s/7s/8s/and 9s) to know that it can become a PITA, but that it can also work flawlessly.
I'm going to do the test in friction mode first though.
I have loosened the limit screw to no avail. I guess I'm hoping the 8s shifters would hold it in gear with the indexing.
