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Post by cusqueno on Jun 20, 2017 14:50:18 GMT
I wonder if anyone on the forum has any views on the use or efficacy of the top pivot spring on rear derailleurs - sometimes called the ‘B’ or rear pivot spring? I ask because I have just bought a Shimano Dura Ace 7400 RD without this spring for £5.00 from eBay. The seller noted the lack of the spring in the listing, but I expected that it was broken or had come unhooked. In fact it had been removed. Did the owner do it to reduce weight (!) or because s/he thought it shifted better without? All DA RDs from the Crane onwards seem to have both pivots sprung - indeed all Shimano RDs that I can think of.
Do I have a bargain (it’s in very good used condition) or is it useless without a sprung top pivot? If so, why should Shimano RDs be different from, say, SunTour. During its glory days SunTour seems to have been totally wedded to springless top/rear pivots - none of its derailleurs have springs there: Skitter, V, Honor, Cyclone, Superbe. Incidentally, the DA 7400 comes from 1984 and so must have been one of Shimano’s first slanted parallelogram ones, after SunTour’s patent expired.
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Post by oldroadietehachapi on Jun 24, 2017 1:28:36 GMT
Try it without the spring. It most likely will not work as well, but may be acceptable. If not, a spring from a Shimano 600 may fit. One of my bikes (a 1986 Trek 2000) is equipped with the Dura Ace 7400 group. I bought the group new, in 1986! Everything changed when Shimano introduced this component group. It was the first Shimano SIS and it worked! The group was stunningly beautiful (my pictures do not do it justice, and yes I have the crank caps). For the first time, a Japanese group was more sought after than Campy. It is said, to sell things, they must either be better, cheaper or different; the Dura Ace 7400 was all three. The Trek 2000 frame and the Dura Ace components seemed made for each other. Since then, technology has marched on; but no component group is nicer looking (say I) than the Dura Ace 7400. All the Best Jim
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foss
Viscount
Posts: 132
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Post by foss on Jun 25, 2017 21:43:04 GMT
If that is the main pivot spring , if it is removed then how would the chain keep it's tension ?
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Post by oldroadietehachapi on Jun 26, 2017 1:09:58 GMT
If that is the main pivot spring , if it is removed then how would the chain keep it's tension ? I have some Suntour and Mavic derailleurs that are made that way. The only tension is supplied by the cage spring. Sounds funky but they work. Cheers Jim
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