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Shimano Positron: How old ?
Hello everybody,
I just bought a very cheap bike that I can leave at the station. It has a 7-speed derailleur labelled "Positron FH400", actioned by a handlebar lever labelled "PPS Shimano". The system provides a somewhat crude indexing, which is handled by the derailleur, not by the lever. I am puzzled about how old this bike can be: Fenders and rims are steel, but can a 7-speed indexed der be that old ? Any ideas ? Jacques |
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#2
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Jacques Moser wrote:
Hello everybody, I just bought a very cheap bike that I can leave at the station. It has a 7-speed derailleur labelled "Positron FH400", actioned by a handlebar lever labelled "PPS Shimano". The system provides a somewhat crude indexing, which is handled by the derailleur, not by the lever. I am puzzled about how old this bike can be: Fenders and rims are steel, but can a 7-speed indexed der be that old ? Any ideas ? You have one of Shimano's many failed Big Ideas there (add oversize pedal threads, the amusingly acronymed Front Freewheel System, U-brakes, Biopace and probably soon Octalink bottom brackets). Anyway, Positron dates from 1977 and was laid to rest before 1984. |
#3
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Jacques Moser wrote:
Hello everybody, I just bought a very cheap bike that I can leave at the station. It has a 7-speed derailleur labelled "Positron FH400", actioned by a handlebar lever labelled "PPS Shimano". The system provides a somewhat crude indexing, which is handled by the derailleur, not by the lever. I am puzzled about how old this bike can be: Fenders and rims are steel, but can a 7-speed indexed der be that old ? Any ideas ? Zog did not deny: You have one of Shimano's many failed Big Ideas there (add oversize pedal threads, the amusingly acronymed Front Freewheel System, U-brakes, Biopace and probably soon Octalink bottom brackets). The "Dyna Drive" pedals, with the bearings inside the threads of the oversized crank were actually a rather good idea. I never heard of any of these cranks breaking at the pedal eye, unlike standard cranks. The offered an arguably real biomechanical advantage, but failed mainly because the bearings couldn't hold up to the stress. "U brakes" were originally offered as a simpler alternative to the excessively complicated rollercam brakes that were in vogue in the mid '80s. Rollercams are now extinct, but U brakes are still in production (though not by Shimano) as they remain popular for BMX/Freestyle applications. U brakes are the best choice for a brake that must be mounted below the chainstays, because it avoids crank clearance problems. Mounting the brakes down there was a silly cosmetic fad for mtbs in the mid '80s, (not a fad that Shimano started...SunTour was more guilty of that.) Biopace was a commercial failure, but a technical success, in my opinion, and I still prefer it over round chainrings. See: http://sheldonbrown.com/biopace Anyway, Positron dates from 1977 and was laid to rest before 1984. That's true in the U.S. market, but it remained semi-popular in Europe for quite a while after that. When I lived in France, 1988-89, Positron-equipped town bikes were offered in every sizable bike shop I visited. I had the impression that they were more popular in West Germany than they were in France. Positron was the first commercially successful indexed derailer system. Sheldon "Histoire" Brown +-------------------------------------------------------+ | ...what is hailed as a new style or a new school | | in literature often consists of doing as a novelty | | what a Victorian did long ago as a joke. | | -- G.K. Chesterton | +-------------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com http://sheldonbrown.com |
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I suppose Syncro 1 & Syncro 2 were good ideas?
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begin quoting Sheldon Brown :
The "Dyna Drive" pedals, with the bearings inside the threads of the oversized crank were actually a rather good idea. I never heard of any of these cranks breaking at the pedal eye, unlike standard cranks. The offered an arguably real biomechanical advantage, but failed mainly because the bearings couldn't hold up to the stress. Perhaps, then, they didn't break at the pedal eye because no-one had them in service long enough? -- David Damerell Distortion Field! Today is Chedday, January. |
#6
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Sheldon Brown wrote:
The "Dyna Drive" pedals, with the bearings inside the threads of the oversized crank were actually a rather good idea. I never heard of any of these cranks breaking at the pedal eye, unlike standard cranks. I'm sorry to tell you that I have (my friend Gareth, early 1990s). |
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