johnwilson09

I installed a new cassette (13-26 compared to the old 12-25) and chain on my Bianchi 10-speed double Mirage, as they were quite worn out. After that I spent a long time trying to adjust the front derailleur, which turned out to be a bit of a nightmare.

I initially used Park Tools' guide, and then Sheldon's guide. The difference was Park Tools advise to release the cable tension for adjusting the L limit, and then pull the cable to maximise tension when adjusting the H limit (in the relevant gears). Sheldon wrote that the L limit should prevent shifting off the low chainring, and the H limit should stop shifting past the large chainring, without scraping the cage of the derailleur.

I moved the clamp down the frame by about 2-3 mm, to give the recommended clearance to the large chainring of 1-2 mm. I also rotated it slightly to align the outer plate of the cage with the chainline. After that I adjusted the H and L limits, so the cage was as close as possible to the chain without scraping, in the relevant gears. I then adjusted the cable tension to get the shift smooth.

On riding this morning, I found that shifting to the large chainring was difficult. The lever felt less responsive - normally it takes 3 clicks to shift up, whereas now it took several more. There was also less resistance as I pushed the lever. Is this due to the cable being too loose? I also managed to shift past the small chainring on shifting down, and the chain came off. So I guess the L limit needs to be tighter? Finally the chain is scraping more on the crossed gear combinations than it used to - before I could use 53:12, but when I try 53:13 now, it needs trimming. I even need to trim on 53 and about the third-smallest sprocket.

In summary my first stab at front derailleur adjustment was a disaster! I get the theory in the instructions, but I don't really understand how the H and L limits and cable tension actually interact to produce a smooth shift. The guides explain how to set it up, but not really how to adjust afterwards. Also the guides talk about how to adjust in the largest and smallest sprockets, but not any other combinations - which adjustments will help reduce the need to trim? If anyone has any advice or links to point me to, I'd be very grateful. Thanks.

joejack951

If you are dropping your chain on downshifts, there are a few things to check:

1. Low stop screw should be set such that the chain just barely clears the derailler cage when using the small chainring/big cog combo.
2. Front derailler outer cage set as close as possible to top of big chainring. 3mm should be the max. Aim for 1-2mm (sounds like you are good here)
3. Be sure your chain is not too long. If the rear derailler can't take up all the slack or can't take it up quick enough, you'll have chain drop issues on downshifts.

53-12 and 53-13 are not cross chaining combinations. 53-26 would be cross chainring. If you are getting chain scraping when using 53-12 and 53-13 and trimming solves it (I assume by trimming you are referring to pushing the long lever further), you need more cable tension. when using the big ring, you should only need to trim when using the innermost cogs on the cassette (20-26 or similar). The derailler cage should be far enough outward already for clearing the chain when using the smallest cogs.

It sounds like you are set up close to correclty but need a few minor tweaks. Do you have a barrel adjuster to help with adding cable tension for the front derailler? If not, adding one will make that much easier.

johnwilson09

Thanks for your reply. Sorry I was being stupid - I meant it was crossed on the 39:13 combo.

joejack951

Ok, that's likely also due your inner stop screw being set in too far (assuming you didn't have this issue before).

johnwilson09

Well after working on it again with the power of a clear head and the extra information, I think I've got to grips with it. I've set the cable tension to try and the biggest range of gears at the high and low end, without scraping or having to trim it. I can't however get the whole range on the small chainring (39) - if I set the tension for the biggest sprocket (26), it will need trimming to prevent scraping on about the 3rd-smallest sprocket. Likewise if I just adjust while on the big chainring (53), I can't get the whole range of sprockets in without scraping. Is this normal? Are there any other adjustments I can make to 'fit in' more gears in my nice area of the derailleur?

Thanks again.

Retro Grouch 

I don't understand your reluctance to "trim" your front derailleur.

joejack951

It is normal to have to trim the front derailler. You can minimize by careful adjustments to tension, stop screws, and cage angle. By setting your stop screws as tight as possible, you will position the derailler for maximum clearance when cross chaining. Having a stiff frame helps too as you can get away with less clearance.

rat fink

It seems like you are working with brifters. I don't if you have barrel adjusters, but one thing I like to do when working without a barrel adjuster on the front derailleur, is this:

1) Set the FD limit screws are set within an acceptable range, so that there is minimal rubbing in cross chaining combinations, (big-big, little-little).

2) Loosen the cable from the FD and loosen the L limit screw just enough that the FD cage moves slightly inboard, maybe two millimeters.

3) Take the shift cable and pull it taught with one hand and tighten the locking screw with the other hand, until it's good and snug. The cable should now have no slack in it, but not be extraordinarily tight.

4) Tighten the L limit screw back to where it was, just shy of rubbing the derailleur cage when in the largest rear gear. If the frame has a tendency for flex, it might be a good idea to leave a little wiggle room; maybe and extra two millimeters.

When setting the H limit screw:

1) Loosen the H limit screw a few turns

2) In the big chainring, small rear cog combo, while slowly turning the crank: gradually pull the FD shift lever further to trim the front as if you were trying kick the chain off of the outside chainring. Note the point where chain starts to fall off.

3) Tighten the H limit screw until you feel it pulling against the shift lever, then tighten another 1/2 to 3/4 of a turn.

4) Reset the shift lever to the default high gear position and then, while rotating the crank, pull the lever again like as if to kick the chain off.

5) The chain should no longer come off of the big chainring when the FD is over-shifted. If it does, repeat steps 1-4, as necessary, until the chain no longer can be shifted off of the chainring. Note: Rubbing is to be expected in the over shifted position, as the this position is normally corrected automatically when the shift lever is released.


P.S. I use this procedure on all my bikes. Done right, it allows me to use any gear combo with absolute minimal chain rub, the FD shifts every time with ease, the cables are always taught so there is no play, or 'deadness' in the shifters/drivetrain, and once the FS is in a neutral position, I can shift the entire cassette back and forth with no rubbing, (except in 53-11, there is very minor skimming. Since that is not a gear that is used for long periods at a time, it does bother me).

johnwilson09

I haven't really had much need to trim before, but now I'm using it more.

That's good advice on the H limit using the shifter. I had it pretty much adjusted, then when I got on the bike and shifted up to the large chainring, the chain still came off. Even though it shifted up fine off the road, when cycling the chain came off - I guess this was because either it was under more load, or I pressed the lever a bit harder. Anyway, I set the H screw accordingly and it all works beautifully now. Thanks for all the info and views.