JunkYardBike

I've just about completed a tune up on an early 90s Specialized Crossroads equipped with a triple Biopace crankset and Exage 300LX front derailleur. These are mated to Shimano STI rapid fire shifters. However, the system absolutely refuses to shift to the largest chainring.

I've run a new cable and Shimano SIS housing to the derailleur. I've tried every godforsaken cable position/tension I can. The front derailleur is not binding at all, as I can manually move it well beyond the largest chainring. I tried setting the shifters on the highest position and securing the cable while the derailleur is propped beyond the big ring, but then the indexing gets out of whack, and it refuses to shift back to the smaller rings.

Can anyone offer any tips or advice? Am I missing something obvious? I suspect the shifter itself, but I'm not sure. I purchased this bike as a pair with another, and it had the same problem after I replaced cables. But, before I replaced cables, the other bike was shifting to the big ring (on this bike, the cable had skipped off the bottom bracket guide, and so wasn't shifting to the big ring).

Thanks,
Patrick

thomson

I had this happen to a triple 105 once, if I understand your issue. Let me restate, you can adjust the cable tension to do either the small and middle ring or the middle and large ring. It turned out to be the lever. I sent it back to Shimano and they sent a new one (with cables).

gruppo

Just a thought, but loosen the front derailleur cable and ensure the shifter is in the lowest (Inner chainring) position, tension the cable and try it again. This sounds very basic, but I've known many good mechanics, including me, who have failed to ensure the the front and/or rear shifters were in their lowest positions before attempting adjustment. The assumption, of course, is it once shifted OK and you haven't done anything other than disconnect the cables for cleaning.

JunkYardBike

I was sure to check that the shifter was in the lowest gear position...several times. I didn't tinker with the shifter at all, just replaced the cable. In fact, I think these shifters are required to be in lowest position in order to route a new cable through. This particular bike was not shifting to the largest ring because the cable had skipped out of the guide underneath the bottom bracket. So, it's possible the shifter was stressed in some way. However, the other bike that came with this pair (exact same setup) was shifting into the large ring until I changed the cable, then it displayed the same symptoms. I'm certain, however, that the problem is not too much cable slack, or securing the cable in the wrong shifter position.

Is it possible lubricating the shifter might have a benificial result? Would spraying it with something like a light teflon grease be advisable?

Al1943

I wouldn't use teflon grease in the shifter. Try WD40, but I doubt that will fix your problem. Have you tried backing out the high limit screw?

JunkYardBike

Yeah - I took it out completely. Well, then I screwed it back in again. The derailleur itself is not binding at all, I can manually move it well beyond the large chainring. The shifter just doesn't want to pull it far enough.

bobo1949

WD 40 stands for "water displacement" formula number 40. It isn't a lubricant although many people use it that way. I don't know why a silicone lub would be bad unless there is a concern about dirt building up in the mechanism.

Retro Grouch 

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