Derailleur adjustment

[ricksavery]

I am about ready to headbutt the wall so please help!!!
I have bought a new chainset (48-38-28), Shimano cassette (11-34) and Shimano LX front and rear derailleurs. I thought I was a reasonably competent bike adjuster (won't say mechanic cos clearly that's cobblers) but I just can't get the front derailleur to sit right without it rubbing on the chain somewhere. I assume that with a 9-speed setup the tolerances are that much smaller but it's driving me to distraction. Has anyone got a similar system with these ranges of gears and did they have similar problems? Can anyone please tell me where I may be going wrong? I know that I may not be giving you all the info you need to answer this but if someone can point me in the right direction I can try it get back to you. Thanks
Rick`

 

[ricksavery]

Update on the problem. I have adjusted the rear mech OK - although slight problem shifting into the largest sprocket, I think I can sort this. The problem is with shifting the front mech from the middle ring to the large ring. The bottom of the inner plate rubs on the chainring itself. I moved the mech up the tube until this wasn't a problem, but the clearance between the mech and the large ring is now about 6-8 mm rather than the 2 mm that is reccomended. Is this OK? It all seems to shift right - going from the largest ring back down to the middle ring meant I had to slacken the cable tension. I wondered if i shouldn't have a smaller middle ring so that the mech can be moved closer to the large ring? I suppose if it works then it is alright ? Sorry to bang on in this long-winded way, but it soesn't seem to be an exact science, or maybe it is and I got lucky :-) Appreciate any comments/advice
Rick

 

[rusky]

Have you tried here http://bicycletutor.com/

Also here http://forums.bicycletutor.com/thread-1995.html

 

[ricksavery]

Thanks for that rusky. Seems very informative on a quick glance. Still not sure about the cage rubbing on the middle chainwheel itself though.

 

[Tigerbiten]

If it a mountain bike front derailleur, if it fitts a 48 outer then it will be, then I think the recomended difference is 12 teeth between the outer and middle rings.
So you may well find a 48-36-26 works without catching.

 

[2Loose]

If it a mountain bike front derailleur, if it fitts a 48 outer then it will be, then I think the recomended difference is 12 teeth between the outer and middle rings.
So you may well find a 48-36-26 works without catching.

That'll be the MAX recommended difference is 12 teeth.

 

[ricksavery]

You're right about the 12 tooth difference between the large and middle rings. I went to the specs for the front mech and that's what Shimano reccomend. So I'm left with three choices: leave as is with the mech set higher than normal; change the middle ring to a 36; replace the mech. Bloody annoying considering a lot of Shimano's chansets have a 10 tooth difference, and there is no way the mech will shift from the middle to the outer without hitting the middle ring - unless you set the mech higher on the tube. Probably should have checked the specs first, but it did not occur to me. Doh!