Debugging an FD problem through three visuals

Question

The front derailleur cable is as taut

as I can get it.

To attach the cable with as much tension, it's first necessary to understand the inside of the barrel adjuster.

And the H limit screw on a Sora FD is so undone (top red arrow)

it does not even touch its footing (bottom red arrow). (The yellow ball is removed.)

Yet when the chain is on the larger chainring and on any of the three smallest cogs, the chain rubs (red arrow)

against the FD cage on the outside.

What else should I try?

If at this point I insert a tougher rubber ball to tighten the FD cable even further, the cage does get off the chain. Is that an indication that my best effort to pull the cable hard before tightening it was not good enough, and I should try pulling harder?

Components: Sora Sora R3000 front derailleur and ST-R3000-L shifter.

Update (question re "judgment" tool, following Nathan Knutson's answer):

The cable goes from one geometric point (bottom red arrow) on the bottom bracket to another geometric point (top red arrow) on the derailleur. There is no tweaking possible to the location of these two geometric points. What is, then, the purpose of the judgment tool?

Answer 1

I'm going to assume you've got FD-R3000 and are pairing with a compatible road double shifter.

The anchor position is adjustible. Follow the procedure in the Shimano dealer manual for your model. It is available at si.shimano.com. There are only two positions so if you don't have the special angle-finding tool you can use process of elimination. Failure to use the right position can cause what you're experiencing. The two different positions slightly alter the lateral point on the arm where the cable is anchored, which tunes the total throw.

All the "long-armed" Shimano road front derailleurs have the quirk of needing a ton of cable tension. The axiom with them is that once the right anchor position is chosen and assuming compatible parts, setup problems are almost always due to inadequate tension. They don't conform to generic instructions for FD setup. A good procedure is start with the shifter and barrel adjuster in the slackest position, then use pliers, a fourth hand tool, or the inner limit to pre-actuate the heck out of the FD as you pull the cable tight while anchoring the cable, then add some more tension as needed with the barrel adjuster after that.

You usually must accept essentially zero clearance between the chain and inner cage in the low gear with these derailleurs.

Another compounding factor to difficulty adjusting the "long arm" FDs is that the cable is anchored in a rather bent position with them, which can make it difficult to simply loosen the anchor bolt and pull out more slack - the memory of the material makes it want to return to how it was. You can try making a marking on the cable where it was exiting the anchor previously in order to be more sure you've actually added tension.

Answer 2

First you should check your derailleur cage is parallel with the chainring, an angled cage cause rubbing.

Nowhere in your question have to mentioned the front derailleur cable barrel adjuster. You mention a Sora groupset so this is a road bike. The barrel adjuster will be on a doentube frame cable housing stop, or perhaps in-line in the housing something like this:

if the lower limit is set correctly, you shoud be able to shift to the small ring, detach the cable, wind the barrel adjuster in (lengthens the cable relative to the housing), then re-attach the cable, pulling it reasonably tight. The cable can then be shortened relative to the housing (made more taught) be winding out the barrel adjuster. This will move the derailleur cage outward.

Pulling harder on the cable isn't going to make it any tighter - it's made of steel and expressly designed to not stretch afterall.

Try watching the Park Tool Front Derailleur Adjustment video on this page, if you work through their step by step procedure you should be sucessful.

Answer 3

(This answer would not have been possible without the answers of Nathan Knutson and Argenti Apparatus.)

(I'm still not certain that this is the correct issue, but I had been wrestling with this adjustment for some time, and the issue has now evaporated once I used the solution below.)

An appropriate setting of the H limit screw is impossible if the barrel adjuster is malfunctioning.

It is not malfunctioning with a capital M, just a minor malfunction.

It's hard to see that that's the issue if one is just looking right/left/above/below the front derailleur.

If you have trouble setting the H limit screw, make sure that you are actually able to add tension in the FD cable through the barrel adjustment.

This answer shows the parts inside the barrel. It's an elementary device. But you may have the illusion that you are adding tension if the cable housing slips/glides on the metal part. The cause could be arbitrary (a tiny bit of oil, ..). Importantly, these two parts are designed to slip on each other. Again, as the answer there mentions, if the two parts do not slip against each other, the user could apply extra force and either keep adding undue torsion on the cable housing, or else simply strip the thread.

Disassemble, wipe any possible dirt/oil. Now make sure (visually) that the metal part does indeed start to protrude when you expect it to.

Now I'm very curious, is deception from a barrel adjuster a common problem? We're no longer in Q&A mode but in fireside chat mode. Add a comment or suggest an alternative medium.

Why? / Illustration:

Perhaps a diagram illustrates the issue better.

The center line is the cable. We're no longer talking specifically about the FD cable, only about cables with barrel adjusters in their middle, not an edge.

A and D are the cable housing. Notice that at all times the cable is under tension, but the cable housing is under compression. For derailleurs, the amount of tension/compression depends on the cog or chainring chosen. The bigger the cog/chainring, the bigger the tension.

C is the barrel adjuster. That's the part you grip. It has female threads. B is the part with the male threads. When B and C are fully threaded, the user cannot even see part B. B disappears inside C.

Here is the important part: this assembly works by ensuring that there is less friction on the threads (between B and C) than between A and B as well as between C and D.

When you turn the barrel adjuster, the relatively high friction between A/D (plastic) and B/C (metal) is what allows you to add or remove tension.

If any grit made its way into the B-C joint, or if any grease made its way to the A-B or to the C-D joint, the entire set-up will no longer work.

It is always prudent to clean the A-B and the C-D joint. No oil should be there. You want as much friction as plastic-against-metal will allow. (If you're following and want to make sure you never strip the threads, you do not want to add a drop of glue in there! The design includes slippage.)

I'm not so sure whether it's prudent, if you suspect that the B-C joint is somewhat rough, to add a drop of oil or a hint of grease. Adding grease there may invite an unwanted turn, either accidentally or from the repeated vibration when riding.