Panza

I posted this here because I didnt see a technical difficulty forum section anywhere ...

It's a Shimano 105 front derailleur.

Issue: The chain keeps on rubbing against the front chain guide outer plate.

It happens when the rear derailleur is in its 5th-9th through highest gears. Gears 1-4 gears there's no rubbing. Happens when I'm in both inner and outer chainrings.



Is this going to be a simple fix or should I take it back to the professional.

I'd just take the metal bracket and bend it with some flat-jaw pliers but I thought I'd see the community's input first.

Homebrew01

Does your shifter have "trim" capability ? Meaning that you can make small movements with the shifter to stop the rubbing.

If not, do you have a barrel adjuster for the front shifter so you can make micro-adjustments ?

shoota 

Omg don't bend it. It just needs to be adjusted correctly and then you need to learn what trimming is.

Panza

I have barrel adjusters for the front and rear shifters.

Bill Kapaun

Did it always rub?
If not, what is different.

RoadTire 

Seriously. Never consider bending anything until you are so good at adjusting everything, and know that you have bent "it" in a crash. Take your time and come here before just cranking on a part or getting out the hammers. The most important thing I have learned, being relatively new to to these new fangled bikes, is everything is a process. If you follow that process, step by step, your bike will love you. Get to the Park Tool web site or get the Park Tool bike manual.

Panza

I went on my first ride with the bike after purchasing it and the chain moved from the lowest rear cassette gear to the wheel spoke and damaged the frame because one of the limiting screws wasn't adjusted properly. The frame and the rear derailleur were replaced, all the old parts were moved to the new frame. I was checking through all the gears to make sure there'd be no hiccups but this much rub isn't something that I remember.

Panza

I'm currently trying to understand

Park Tool Co. » ParkTool Blog » Front Derailleur Adjustments

and

https://techdocs.shimano.com/media/te...9830621301.PDF

This part here but it's a bit confusing, I'm gonna have to reread it a few more times...

I'm trying to fix a "Tail too far inward" issue.

RoadTire 

Ok good for you to check the bike out thoroughly ahead of time. My fist impression is the LBS is not doing their job correctly or checking their work. Also, I'm not the best person here to give advice, but will try not to mis-guide you either. Looks like a clamp-on FD, right?

1) shifted onto the largest front chain ring, and smallest rear cog (that would be your highest or fastest gearing, just like a car) as PT instructions?
2) before you move anything - use a small marker on both pieces so that you can reference exactly were you started.
3) Can you get a top-down picture for us to look at before you move the FD? Need to make sure the problem is the chain line, not the FD limit screws and cable tension.
4) If it is a mis-installed FD you will end up loosening the FD clamps and rotating is slightly, then checking your work.

Don't skip any steps. Be prepared to put it back the way you found it, in case that is not the problem.

Can you get a different mechanic to look at it at the LBS?

kleng

Your saying the rubbing is occuring in the largest cogs? when using both the small and large chainrings

Is it the inner out outer plate of the front derrailleur cage that is rubbing ?

You can rotate the FD, to make the front of the cage more parrallel to the front chainrings, by loosening the bolt slightly where the FD mouting band is and rotate it. This will move the tail of the cage out more. Be careful the high tension of the derallieur cable doesn't pull the FD down when you loosen the mounting band bolt, always have it in the small chainring setting when adjusting it.

In the techdocs, I think you need to look at point 1, the low adjustment, and turn B, until that 0.5mm clearance occurs.

Panza

I tried the barrel and the H outer limit screws but the problem is still present, when I try to tighten the cable myself the issue goes away so I think the cable may not be tight enough, I just don't know how far to move the cable. Perhaps it's trial and error?

RoadTire 

Nope, not trial and error. Where is it rubbing: FD Front Inside or FD Front Outside?

Go back to the Park Tool site. The basic steps to FD adjustments are (if I remember correctly, and I just did mine 2 days ago, following the process):

Shift into the lowest gears. Set the FD L limit screw. Barrel adjusters almost all in, the FD cable tension will be very low. If not the cable may not be installed correctly.

Next shift RD to highest (smallest) cog, then go back to the FD.

Set the FD H limit screw by pulling the cable and adjusting until you just get a good shift without throwing the chain off the outside. Now with minimal barrel tightening you should be able to shift to both the small cog and large chain ring without difficulty.

But answer this first, and get us a picture if you can: Where is it rubbing: FD Front Inside or FD Front Outside?

Bill Kapaun

That's a rather poor approach, especially when someone posted the link to the PARK website!

You really should make whoever did the work make it right!

RoadTire 

There is always that. In this case, going back to comment in Panza's earlier thread about the RD busting out of the frame, maybe the LBS needs to be held fully accountable for getting it right before the bike leaves the shop. Needs to be test rode and proven before accepting it maybe. But I sure don't trust LBS mechs much anymore until you find a good one and then stick like glue.

Panza

I really should, its unfortunately far away for me though, so I was considering taking to a different mechanic that I see more often. I made some reasonable adjustments on it to keep it within reasonable limits and to stop the chain from rubbing so much, nothing too far from what the original bike maker had done though. Quarter turn of the screw.

cny-bikeman

OK, back to square one - and the following is for others posting problems as well.

First, please do not refer to "highest/lowest," "gears 5-8," etc, but instead refer to the relative position or cog, such as "furthest out rear cog," "middle chainring," "smallest three rear cogs." Fortunately in this case the OP specified the chain is rubbing on the outer portions of the front derailleur cage so it would appear safe to assume that the OP has an 8 rear cogs and the problem is on the smallest/outer ones. OP - please let us know if that is incorrect, as everything suggested flows from our original understanding of the problem.

Secondly, it's critical to include full info from the start, especially when the problem started, any maintenance or incident that occurred just prior, and exactly what you have tried so far ("adjusted the derailleur" is not specific enough).

Third, bikes are a mechanical system. They work in a logical manner governed by the laws of physics. Applying trial and error OR blindly following a procedure will neither help in the short term nor in the future. One has to think about WHY a problem is occurring and whey a procedure is being done to correct it. Don't underestimate the power of observation and logic to solve a problem even for something you have never done before.

Now, given the above:

Please explain again whet position in the rear (most outer or most inner) are giving you problems.

Assuming the problem is when on the outer rear cogs, what exactly did you do to adjust the derailleur, in order? This will be tedious, but if you don't have a close resource there's no other way to tell where you are going wrong. We also need pics from above the derailleur that clearly show its alignment to the chainwheel, both when rubbing and when clear of the chain.

Thanks.

FLJeepGuy

Based on the pic you posted and your statement that you think it's a "tail too far inward" issue, my guess is that the entire FD assembly is not properly mounted and aligned on the frame. This is usually the first thing to check before playing with cable tension and the limit screws. If the FD is not properly positioned, no amount of adjustments will correct the issue.

Here is a summary of how I make my adjustments (others might have a slightly different process, but this works for me):

1) Turn all FD barrel adjusters to their most inward, loosest position.
2) Shift the front to the middle ring and the rear to the largest ring. Stop the wheel and stop peddling and move the front shifter to the lowest setting to relieve tension on the cable.
3) The FD assembly should be positioned to that it's outer edge is perfectly parallel to the largest ring on the front with about 2-3mm height clearance between the FD and the cogs on the large ring at the FD's nearest point. You can push on the FD with your thumb to move it outward to check position. If it's improperly positioned, loosen the bolts holding it to the frame and carefully adjust the entire assembly's angle and height to bring it into proper alignment and clearance. Once there, tighten the mounting bolts back in place.
4) Turn the cranks and shift front and rear to 1 and 1. Loosen the cable bolt to allow the cable to slide freely on the FD. Use the low limit adjustment screw to position the inner rail of the FD as close as possible to the chain without rubbing when pedaling.
5) With the cable bolt loose, pull on the end of the cable to remove ALL of the cable slack and tighten the cable bolt. Get the cable as taught as possible by hand.
6) Turn the cranks and shift the front and rear to the highest gears. You may need to back out the high limit screw slightly if the FD won't quite shift up to the largest ring. If loosening the high limit screw doesn't get it there, use the barrel adjusters to slowly tighten the cable until it shifts up.
7) Once the shifter and chain are both in the highest position, use the barrel adjuster to move the FD so that the outer rail is as close as possible to the chain without rubbing. If you're running out of adjustment room in the barrel adjuster, turn it all the way in again and go back to step 5 as you didn't get the cable tight enough to start with.
8) Slowly tighten the high limit screw until it just makes contact. You should not be able to manually move the FD any farther out.

At this point, everything should be in correct adjustment. Trying running the RD up and down through the gears with the FD in the highest and lowest settings. Nothing should rub at this point. You may have to make minute final adjustments to the limit screws for low gear and high gear clearance and the barrel adjuster for smoother shifts. If you're making big adjustments at this point, start over. Remember, no amount of adjusting will correct for an incorrectly mounted and aligned FD assembly.

Hope this helps. My technique may not be perfect, and I'm open to suggestions as well from the more experienced folks out there.

Homebrew01

If everything functions well, except for the rubbing, and there is no trim function, then I would think a minor increase in "cable tension" would move the derailleur cage over a little bit to stop the rub.

The H and L screws are not part of the problem and you should leave them alone as long as the actual shifting up & down is ok.

cny-bikeman

The OP said that the rubbing occurs on the outer cogs on both chainwheels. That logically cannot be only cable tension, as the inner position is unaffected by cable tension. The OP should not experience rubbing that would require moving the front derailleur slightly (trimming) as soon as the 5th cog largest cog - far too soon. If the inner adjustment is correct and the chain rubs that soon then there has to be a problem with either derailleur rotational alignment, cage width or distortion of the cage/pivots. As far as the outer is concerned, the OP said that increasing cable tension solves the problem, so there is a problem with cable tension OR incorrect cable pull. Assuming the OP has OEM levers and derailleur at least part of the problem on the large chainwheel lies in the incorrect cable routing at the clamp - note that it passes to the right side of the clamping bolt, which is incorrect.