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shimano bicycle chain

shimano bicycle chain

My bicycle front shimano gear does not shift from highest to middle one?

I have tried adjusted the side to side screws. they appear to be perfect. It changes from (front) lowest to middle and then to highest. But when I try to go back it wont go from highest to middle (only makes rattling noise by touching chain). Once I step down to lowest it goes from highest to lowest skipping the middle like a charm. So highest to middle is the problem? What should I do?

The most probable explanation is that your front derailluer (FD) cable is too tight. You can loosen it one of two ways. First, look to see if the cable passes through any adjuster barrels. These are typically found on the shifter where the cable exits, or else on the downtube near the junction with the headtube. If you find one, turn it clockwise to release tension from the cable. Alternate between checking the shifting (large to middle chainring) and adjusting a quarter turn at a time. If you don’t have any adjuster barrels to work with, or if the ones you have are already screwed in all the way, undo the cable anchor bolt on the FD, let a little bit of slack through, and re-tighten it. If you find that the derailler will shift down after you do this, but won’t readily shift back up, then you’ve loosened the cable too much and you need to add more tension either by turning the adjuster barrels counter-clockwise or by pulling the cable taught through the anchor bolt.

If you can’t seem to strike a happy balance between upshifting and downshiting, or if you are having trouble shifting in both directions, check to make sure that the FD is positioned correctly. Shift to the middle chainring so you can get a good look at the outer plate of the FD cage relative to the large chainring. Looking from above, the outer plate should be parallel to the large chainring, or else angled inward very, very slightly towards the rear. Looking from the right side of the bike, you should be able to see a 2mm gap between the top of the teeth of the large chainring and the bottom of the plate of the FD.

If the FD is positioned properly, and you can’t seem to fix the problem by adjusting the cable tension, check to make sure that the cable is running freely through the housing. To do this, undo the cable anchor bolt and try pulling the cable back and forth through the housing as well as running the housing up and down the length of the cable. The interface between the cable and the housing should be nearly frictionless. While you do this, make sure that the chewed-up part of the cable where the anchor bolt pinches doesn’t enter the housing, or else you won’t be able to get a good feel. If the cable has trouble moving freely through the housing, pull it out of the housing and wipe it off–if it is kinked or if it rusty in the sections that run within the housing, replace it. If the cable is ok, squirt some oil in the housing, put the cable back in, and test again to see if the cable runs smoothly. If it still doesn’t, replace the housing.

Here are a few more questions to consider:

-Was either the FD or the front shifter purchased aftermarket and/or installed by someone other than a professional mechanic?

-Does the spring in the FD seem nice and strong?

-Are the shifters indexed? Do they click like they’re supposed to?

-Is the crank bolted on tightly?

-Is there a lot of play in the bottom bracket bearings? Is the bottom bracket spindle the correct length?

It would take too long to write out the fixes for all of these potential problems, but please edit your post if any of them apply. Ideally, diagnosing a bike is less of a monologue and more of a dialog. Keep in mind that even very inexpensive, low-end, and old components work well when they are well adjusted (provided that they are not broken) so with some persistence, I’m sure we can figure out how to get your front shifting working again.

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