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DA 7900 shift lever won't shift up

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DA 7900 shift lever won't shift up

Old 07-05-13, 06:34 PM
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jesnow
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DA 7900 shift lever won't shift up

After about 3 years of (heavy) use, I'm having some serious issues with my
Shimano Dura Ace 7900 setup. The mechs front and rear are working correctly,
clean and lubed, the cables run easily, never crashed. But the right lever does not shift up
very well, and as of today, not at all. First the click faded away, then it stopped working
unless I slapped it (ow!) now it just don't work. I can get it to shift up (eg to get the
cable out) by clamping the wire with visegrips and pulling like hell while shifting.

Not a cable issue, not a mech issue, this is purely a shifter issue.

OK, so the obvious things I tried: Blasted the thing out with WD40. No change,
off with the hood, take off the inspection cover, yes it is nasty inside. This bike
has seen heavy use. Blasted it out with brake cleaner (which is pure TCE). At least
now it's clean as a whistle, and I can see the pawls operating. Nothing looks broken
or defective.

Shifting down encounters no resistance, but shifting up once again requires some
serious force to be applied to the rotating barrel (using a small screwdriver to push)
to get it to engage and shift. If you look at the Shimano installation video, it is clearly
supposed to shift up even when no cable is attached. ("Click the upshift lever until
it has reached the highest-gear position to install the shift cable").

Using the solvent/WD40 approach makes it now a little easier to force the barrel to turn.
Hope? I have the whole lever in a bucket of parts cleaner overnight to see.

So: why is it not shifting up? Is the internal spring broken? Is it just gummed up in there?
Is there any way to get it open to see/fix? Or am I just SOL and $600 for a new pair of
levers? I noticed a lot of salt (from sweat I guess, but not very salty) everywhere, maybe that's
up inside the barrel where the spring is. Solvents wont touch that -- Put it water?

The left lever has done this off and on too, most notably and reliably in races.

Any help or insight would be greatly appreciated. Shouldn't I be getting more than
just 33 Tkm out of a shift lever?

jon
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Old 07-05-13, 08:07 PM
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Kimmo
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Haven't worked on any 10s STIs, and they're a lot different... the only advice I can give is it almost certainly won't help to force anything. Sounds like a rebuild is your only chance, and I'd guess something inside is bent.

If you want to avoid such hassles in future, I'd recommend Ergos or Doubletaps. Ergos are a lot more simple and robust and pull more cable per shift which is a lot more reliable, and Doubletaps are even simpler and pull even more cable.

The SRAM cable pull is so huge, you hardly ever need to touch the barrel adjuster. It just works. And it's hard to imagine what could ever go wrong with a Doubletap except for eventually wearing out.

You can just get the levers and a Shiftmate. If you have a triple I'd recommend Ergos instead of Doubletaps.
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Old 07-05-13, 08:08 PM
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If there's salt, there's probably rust also. You're right that nimeral solvents don't do a good job with salt, so a water flush may be called for. Use hot (from the tap, not boiling) water, and flush it well until you don't see any salt, then again in case you missed any. Shake it out, and dry it with a hair dryer, and spray with light oil.

Since you have some movement, thread an old cable, make a loop so you can grab it and work the lever back and forth against hand tension. Hopefully the mechanism will get looser as you work it back and forth. If you make any headway, stay with it until it feels normal, then flush with WD-40 or whatever to flush out any rust or small particles.

Meanwhile cross your fingers, and do something to improve your Karma, because all this is iffy, and you have an equal chance of being SOL and out big bucks (or pounds) too.
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