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Old 07-30-10, 12:44 PM   #1
bosbike
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Shimano Dura Ace 7800 Rear Derailleur Shifting Issue

Hello,

I was hoping someone could enlighten me on an issue I am having with my Dura Ace 7800 derailleur:

Recently I switched from Ultegra SL triple to Dura Ace 7800. It is a complete DA setup (except brakes) including chain, cassette and crankset.

My issue is with the rear dérailleur shifting. Although the rear derailleur is aligned (no mis-shifts or skipping gears or anything like that), and my down shifts to larger sprockets (i.e. from from 11t to 13t) are smooth a silent, my upshifts to smaller sprockets (i.e. from 13t to 11t) are not smooth nor quiet.

Every up shift, I experience two things: I sharp change in the gear (i.e. if I kept force on the pedal my leg would jerk at the change of gear) and a relatively loud slam of the chain to the proper gear.

Any input as to what is causing this is greatly appreciated!

Thanks!

-Franco
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Old 07-30-10, 12:57 PM   #2
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Its normal. At least on mine it is. The chain is dropping down to a smaller cog and the ramps make it go quick. As such if I have pressure on the down shift it is like slamming the chain in the cogs. And with the smaller cogs the chain is less likely to be engaged than if it was on a larger cog.

Or imagine this. You are responsible for moving a 4X8 sheet of plywood up and down an 8ft tall wall all by yourself. When you move the plywood up the wall you are under it pushing it up, it is a slow gradual climb up the wall for the plywood and when it reaches the top level it slides into place easily. But once on top when you have to move it down there is nothing to catch it at the bottom of the wall since you have to be on the top with it in order to push it over the edge. It drops to the next level rather quickly and loudly instead of gradually.

Listen to others and if yours is worse than others then maybe look at it closer.
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Old 07-30-10, 01:22 PM   #3
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It sounds to me as if your derailleur may be hesitating on the up-shift. If this is the case then try a 1/2 turn clockwise on the barrel adjuster.
If the cables and housings are old consider replacing them. Excess friction in the housings can cause hesitation on the up-shift (toward a smaller cog).
Also ease up on the pedal pressure while shifting.
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Old 07-30-10, 02:03 PM   #4
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Im glad to hear that it might be normal. As to the condition of the cables, they are new (just changed both cables and housing). The plywood analogy helps alot though and I hope it really is the case. Please continue to confirm that this is normal and that I should back off on the pedaling when upshifting (to a smaller cog).

However, I do recall that my ultegra sl triple wasnt quite as loud as this -- is there a reason for the difference? Perhaps ultegra sl derailleur (given that it is newer) is more refined than DA? (Just me thinking out loud).
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Old 07-30-10, 03:41 PM   #5
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The D-A derailleur should shift at least as smoothly as an Ultegra.
Most shifting problems are not caused by a derailleur. Usually it's the shifters, cable housings, setup adjustments, or hanger.
Is the short housing loop just before the derailleur long enough? There is a standard length. If it's too short it will cause hesitation.
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Old 07-30-10, 06:46 PM   #6
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Quote:
Originally Posted by Al1943 View Post
It sounds to me as if your derailleur may be hesitating on the up-shift. If this is the case then try a 1/2 turn clockwise on the barrel adjuster.
This is a pretty good possibility. Whenever I overhaul a bike and/or change derailleur cables I always adjust the rear derailleur cable tension until the downshifts and upshifts aere about equally "eager". That is until they are both about the same quickness. A too loose cable can make the downshifts a bit sluggish and the upshifts too fast and a bit harsh. A too tight cable will do the opposite.

If you changed the cables recently some refining of the tension setting may be needed after a few rides as the new cable beds in and effectively becomes very slightly longer.
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Old 08-02-10, 04:49 AM   #7
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Thank you all! Seems like hesitation maybe my issue but we shall see. I dont think the loop at the rear derailleur is too short but I wouldnt know. I took a short loop yesterday and it seems like the shifting is ok.. only sometimes on the downshift did I notice the slamming (that versus the trainer) sooo I have decided to "bed" the cables in and see where it goes. THanks!
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