What's wrong with my DA read derailleur?
 

First step of installation after attaching to hanger is align the pulley with the outside of the small cog. I loosened the top adjustment screw as much as it goes, but the farthest the pulley goes to the right is in between the first and second cogs. Any ideas what may be wrong?

Tried a spare Ultegra derailleur I have and it works fine, so it's not a bent hanger or something like that. It's something with the derailleur. Thanks.

Is this a new model or blast from the past?

Sorry--it's the 10 speed RD-7800.

Is the chain on there and the two derailleur pulleys vertical? If not, the coiled up cage can bump into the body of the derailleur and not move further out. With a chain in place, it pulls down the cage out of the way.

Chain was not on, but the instructions say to put the chain on after the pulley is adjusted. When I tried is with the chain on it still wouldn't shift to the small cog.

Assuming when you say 1st and 2nd cogs you mean 1st and 2nd gear? Some folk get this stuff mixed up. Maybe you need to try to mount the derailleur without the hanger, some were never intended to use a hanger like mine. Also when you monted the derailleur did you rotate it fully clockwise till it stopped then threaded the mounting bolt? And when tightening the mounting bolt did you rotate the derailleur fully counterclockwise when the bolt was being secured? If not you could damage the derailleur or the hanger but probably not likely.

Do you get a chattering noise when in the smallest cog? if so you need to readjust your H screw.

It's the small cog. The hanger is not a replaceable one--not sure it's still called a hanger but I thought it was. It is mounted properly (I've installed enough of these to know I at least did that part correctly). I can't shift to the small cog now matter how far I turn the screw.

Is the cable connected to the rear der? If so, disconnect the cable and then adjust it. I think you may have pulled the slack out when it wasn't in the highest gear.

I know its infuriating that we ask so many easy installation questions but its either one of those or the derailleur is bent.

When bolting on the derailleur, did the B adjust screw get jammed against the side of the dropout instead of lining up with its stop?

When viewing the derailleur from above and from the rear, are the jockey wheels in line and in the same plane with any one gear in the cassette?

Do you have a spacer or "dork disk" behind the cassette that can be removed?

Nope, this was done without the cable connected.

Max:
1. Not infuriating at all.
2. Adjustment screw was not jammed.
3. They were in line in between the 12 and the 13 (it's a 12-27 cassette).
4. No dork disk.
I'm perplexed.

Check that the plate/washer on the cable fixing bolt is orientated right. I did this once and spent hours trying to figure out what was going on since I had the same symptoms as you. Got out the hanger alignment tool and had a go. Turns out I had the little hook on the plate in the wrong spot. The bit of the angle washer that hangs over should be pointed towards the barrel adjuster. It should be perpendicular to the cable and not parallel, and not shielding it if you can see what I mean.

Getting this washer in the wrong spot will ensure that the body can't swing out enough to get down onto your smallest cog.

Check this link out:

http://techdocs.shimano.com/media/te...9830609123.pdf

Thanks, but this is a problem even before installing the cable. It's supposed to be able to line up under the smallest cog, and it doesn't, without the cable even being attached.

I reread the original post. Only one more question. You said that you backed out on the adjuster screw as far as it goes. Did you mean that the screw stopped coming out or that it came out so far (I think that it might come out completely) that further adjustment would have accomplished nothing.

You pritty much have it nailed. If the screw is our far enough, (check the screw and adjacent surfaces for burs) the cassette is in far enough on the wheel and the derailleur is not bent then ??? send the bat signal. Start checking out the derailleur exploded view for missing or misassembled parts from Shimano

Most derailleurs that I have worked on will go quite a bit farther out then the last gear.!@#$%$

Right, I tried going both directions just to make sure I wasn't going crazy. The screw almost came out completely. Going the other direction just made it worse.

About the cassette not coming out far enough or coming out to far. If you are using the CS7800 cassette, there is an instruction on the Shimano site that requires the installation/use of the "low spacer" when installing on a 9 speed hub. The spacer appears to be 1mm thick and the instruction is SI-1Z80A. If this spacer comes in the cassette originally it will have to be removed for a 10 speed hub. Don't know if this helps but it opens a new line of investigation. If not the derailleur then possibly the cassette.

That's not it, since I've had this wheel/cassette combo on other bikes and worked fine. Also, it works fine on this bike with the Ultegra cassette. I think something's wrong with the derailleur. Perhaps I'll try installing it once more just to see if there could have been anything wrong with the initial install.

Sorry, out of ideas. Let us know what you find. This looks like one for the library.

Good Luck

With all of the possible causes you've eliminated I've also concluded there is a manufacturing defect in the new derailleur. Shimano has a 3-year warranty on Dura Ace so you should have no problems getting it replaced.

I ran into the same problem with a Dura Ace RD-7800. My problem was that I rotated the L shaped plate type thing that fixes the cable the wrong way. It was preventing the derailleur from shifting all the way to the highest gear. After 2 hours of racking my brain, it was one stupid orientation of that L plate.

1) Is the cable already attached? If so, try loosening it. (never mind - saw that it's not attached yet)
2) Are you adjusting the correct limit screw?
3) Is the derailer actually hitting the limit screw? My guess is not. If it's not, check if it might be hung up on something by pivoting it backward and forward. Also try pulling the cage down as DannoXYZ suggests.
4) If it's not hung up on anything, can you move it out by hand? If so, the derailer may be dirty or sticky, or the spring may be defective.

Is this a brand new derailer or has it been used before?