gitarzan

I replaced the old Altus with a new Deore 581 RD and the twister shifters with rapid-fires.

I set up the RD as always, setting high and low travel and adjusting the indexing knob so that all gear changes are perfect when the bike is in the rack.

But, when I am riding the chain goes right over the big cog and off the cassette upon a big shift, say a rapid fire up 3 cogs. I;ve not been able to adjust this to a satisfactory manner.

Any suggestions?

FBinNY 

Try tightening the inner limit a bit more.

The best test for a limit screw isn't to shift via the levers or twisters, but by pressing directly on the lower RD body, or shifting by drawing the bare wire away from the downtube like a bow string.

Direct shifting bypassing the shifters ensures that you have a true and positive limit screw setting, and not an illusory one based on a lever click. You need to find the limit setting that's bulletproof against over-shifting, yet allows a crisp shift from the second sprocket to the largest. Sometimes that's a delicate balancing act between a tightly set limit screw and a tighter trim setting via the barrel adjuster.

JonathanGennick 

How did you set the low-limit? With the bike in the rack, and when pedaling, push the the derailleur by hand to move the chain towards the largest cog. Does the chain drop off into the spokes?

Edit: FBinNy says it better than I did.

peripatetic

But note: both are pointing out the importance of testing the inner limit screw by moving the rear derailer withOUT using the twist shifter. The limit screw needs to be set to put an absolute limit on the movement of that derailer.

Retro Grouch 

Have you ever had the derailleur hanger alignment checked? Whenever I encounter a shifting problem that doesn't respond to basic tuneing efforts, the first thing that I do is to check the hanger alignment. That almost always fixes it.

rydabent

Dont overlook the adj of the "b" screw. If that adj is too wide it may make the chain too sloppy. My Sram 7 is adj to 6mm to the large sprocket for instance. If that and all else fails just tighten the limit screw about 1/8 th of a turn at a time and test ride.

gitarzan

OK, posting my results... Looks like just about everyone was right

Thanks for the advice. I did notice that the Indexing knob was almost at it's outer limit, so I twisted it back in. I suspect that adjustment did little after all I did later but may took some relief from the threads in the long run.

I never thought of adjusting by moving the derailer only, and you were right, there was more movement to go, quite a bit. I have filed this one under the remember column and will do it that way from now on. What an obvious oversight I have been making.

I did check the b screw, it seemed OK.

Basically that issue. And I did a dumb one here. I cross threaded the derailer. Duh.

It was off by 2 or 3 degrees at least. I pulled the derailer and lucky me the bike had a removable derailer hanger. I pulled it and looked at it.

Luckily, I had a loose derailer bolt that went to some old stuff so I carefully threaded in from the left side, removed it and carefully screwed it correctly from the right, trying to clean up the threads.

I then put on the RD and it wanted to cross-thread again. So I tried one more time, holding the hanger a little the other way and BAM it threaded on. I popped on the hanger with the RD attached and everything just fell into place form there on...

THANKS EVERYONE

Kimmo

Ew, cross-threaded RD mount : /

Guaranteed to mess up your shifting.

Captain Blight

Just for what it's worth:

Our derailleurs' movements are controlled by cable tension. Almost all shift issues can be traced to cable tension being improper in some way. If cable tension adjustments don't do the trick, then the next step (*always* start with cheap and simple) is to look at alignment issues.

Kimmo

/waits for a Di2 owner to come along and get his gloat on

Captain Blight

Oh, computers are just a fad.