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I have a bike set up with a dura ace 7800 derailleur, specifically listed as a 9 or 10 speed model. I am interested in getting it working in the 10-speed configuration. Two things:

  1. I remember reading somewhere that you have to rout the cable a certain way to get it to work with 10 speeds, but I can't remember how to do so.
  2. I can't get it to rest in the bottom gear even when the limit screw is all the way out and the cable isn't attached. I can easily force it into place, though. I am considering taking out a spacer from behind my cassette that the instructions said I would be needing.

Any advice?

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up vote 1 down vote accepted

There are 2 limit ("H", "L") screws and one tension ("B") screw on Shimano derailleurs. They all 3 need to be adjusted properly. My guess is you need to adjust the B-tension screw and/or the cable tension. There are excellent instructions at Park Tool and I would advise that you carefully follow those instructions in order, and see how it goes.

DA 7800 should not require special cable routing unless you're using it with older shifters, but that's not likely to be the case since you said 10-speed.

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I'm going to poke at the bike a bit but I think you have me on the right track. Thanks. – user973810 Feb 9 '12 at 4:03
For the record, it was the B. I tightened it up a fair bit and the chain slid right into the small cog. – user973810 Mar 7 '12 at 20:10

The Dura Ace 7800 rear derailleur has two different positions for the pinch bolt/clamp that holds the cable in place. One of these positions will limit the derailleur's range, and make it incompatible with 10 speed systems.

If you loosen the bolt, re-orient the clamp, and tighten again, it should work on your 10 speed system without any problems.

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Don't know what to say. I didn't have any trouble with mine in 10 speed configuration. I didn't do any special cable routing, just backed the limit screws all the way out (I seem to recall there's an outer AND inner limit screw?) and tweaked until it worked... Only thing of note that I remember at all was moving one of the spacers on my cassette so that it would freewheel (cassette I'm using says it's not compatible with the wheels I use and indeed turns the bike into a fixie, but I found that moving a spacer makes it compatible and lets it freewheel).

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