Bicycle Mechanics - Rear derailleur question

OK, so despite the kind people who told me I could probably squeak by using my Tiagra rear derailleur with an 11-32 (9-speed) cassette, I decided to swap in a Deore RD-M531. I frayed the cable doing the switch, but replaced that and that part, at least, seems to be OK. Even so, I can't seem to get the shifting correctly.

The problem I'm having is that when I get to the bigger cogs, it's jumping ahead, skipping cogs. It shifts great on the four or five smallest cogs, then I get to one where I hear it dragging and on the next shift it skips a cog. Coming back down to the smaller cogs, it refuses to shift off of one or two of the big cogs and then skips a cog on the next shift.

I've tried using the barrel adjuster to loosen the cable, but when I go looser it won't shift from the smallest cog to the next biggest and even then I have some problems with the bigger cogs.

I've browsed through search results on this site. I've read Sheldon Brown's article on the topic. I've read the Park Tool website article on derailleur adjustment. I've read the adjustment section in Bicycle Magazine's Bicycle Maintainence and Repair. I've read the relevant section in Lennard Zinn's Zinn and the Art of Road Bike Maintainence. I watched the Bicycle Tutor video. These things just aren't helping me.

I'm using Tiagra STI shifters, if that makes any difference. I took the Deore derailleur off an 8-speed bike, but it's my understanding that it is a 9-speed compatible derailleur. Let me know if that assumption may be wrong.

I'd really appreciate any help anyone can give me with this. Thanks.

Did it worked when u had the Tiagra RD on?

U sure all cogs are installed facing the correct direction?

U using a 9-speed chain correct?

Yes, it worked with the Tiagra RD, except there was a little issue with hopping when it was on the little chainring and the big cog. I'm pretty sure all the cogs are facing in the correct direction. (On a side note, wouldn't the spline alignment prevent me messing that up?) I'm using a Shimano HG53 9-speed chain, which I just installed. It's a Shimano HG50 cassette, FWIW.

Yes, it worked with the Tiagra RD, except there was a little issue with hopping when it was on the little chainring and the big cog. I'm pretty sure all the cogs are facing in the correct direction. (On a side note, wouldn't the spline alignment prevent me messing that up?) I'm using a Shimano HG53 9-speed chain, which I just installed. It's a Shimano HG50 cassette, FWIW.

No, the splines are symmetrical. You can get it wrong. Unlikely, though, as it's pretty obvious which way round they go. Sounds like worn chain and/or cogs to me. Have you ever set up a rear mech before out of interest? I'm only asking because it can be a lengthy process the first few times you do it.

Loosen your cable tension a half turn or more.

It sounds like you've spent a lot of time fine-tuning it and can't get it to work, so it's probably not just a slight turn of the barrel adjuster. It shifts OK at one part of the gear range but gets worse as you shift up or down, right? There's a very good chance you have the cable routing wrong at at the derailer's pinch bolt. There are two ways of routing the cable there (possibly more if you're especially creative).

Go to this link:

http://www.sheldonbrown.com/derailer-adjustment.html

and go near the bottom (or search the page for "alternate cable routing"). That should explain it.

The way shifters work is they pull a specified amount of cable per pull. That cable is attached to the RD which is basically a lever. The problem is, if the cable attaches at the wrong point on the RD, then it will move the RD either too much or not enough per shift. While you can get it in tune for part of the gear range, as you keep shifting out of that range the little bit of extra (or too little) travel per shift adds up until it starts skipping.

I bought a bike where the shop accidentally set it up with the wrong cable routing. Took me a week of fiddling and cursing to figure out what the cause was. After re-routing the cable it shifts perfectly.

Replace the cable housing connected to the rear derailleur.

It sounds like you've spent a lot of time fine-tuning it and can't get it to work, so it's probably not just a slight turn of the barrel adjuster. It shifts OK at one part of the gear range but gets worse as you shift up or down, right? There's a very good chance you have the cable routing wrong at at the derailer's pinch bolt.

Wow! You sir, are the man! :thumb:

I suppose I should have mentioned that I also just installed new cables (and, yes, to answer a previous respondent's question, this was my first time for both installing a derailleur and replacing the cables). I had unwittingly used the "alternate routing" (and, BTW, completely ruined the new cable in the repeated attempts to get this working -- good thing I bought two!). I just switched it over to the standard routing with yet another new cable and now it shifts like a champ.

Don't I feel like a fool for listing Sheldon Brown's article in what I had read when, in fact, it had the answer all the time. I guess I should have read it more carefully. :o

Many thanks to everyone who responded.

Mr. Underbridge, you have my undying gratitude!

Well live and learn. I would had automatically use standard routing 'coz anything sticking out I don't like.

No, the splines are symmetrical. You can get it wrong. Unlikely, though, as it's pretty obvious which way round they go. Sounds like worn chain and/or cogs to me. Have you ever set up a rear mech before out of interest? I'm only asking because it can be a lengthy process the first few times you do it.

You CAN'T get the cogs on backwards on a Shimano cassette!