Hello, I知 hoping to find some help with a bike front derailleur function issue. I知 working on my brother痴 bike (Trek 1220 Road Bike). Just doing some general maintenance. Bike has a triple front derailleur. I completed making sure the rear derailleur was tuned well and moved onto the front. I noticed the front derailleur cable was slightly frayed at the end and decided to replace it. I have completed tuning the front derailleur and all works well while mounted to my work stand. Once I get on the bike for a test ride is when the problem starts. Shifts work well in the two smallest chain rings in front but when I move to the largest chain ring the shift is smooth but when I push on the pedal with any force the chain wants to drop of the large chain ring and makes lots of noise. I知 not seeing any indication that the derailleur cage is touching the chain once on the chain ring. Since I知 not able to replicate this issue while on my bike stand I知 having trouble diagnosing the problem.



Thank you,

Might be as simple as not putting the cable correctly though the pinch bolt. You didn't futz the limits did you?

If it's a Shimano FD, then the part number will be stamped on it somewhere. Usually on the back side. Maybe it'll have to be taken off to see. It won't be anything you see written on the part of the cage you see from the right side. But that might help others if that's all the information you can get from it. A picture of it as well as a picture showing the cable in the pinch bolt might help.

Is there a in-line or barrel adjuster anywhere on that cable? Turning it counter clockwise a 1/4 turn or more might help. Or just pulling a little bit more cable through the pinch bolt to leave a slightly longer widow end. But if you messed with the limit, that probably won't help.

If you do find the part number of the FD and it's Shimano, then go to their technical documentation site and plug it in. Then look at the DM. If no DM, then the SI or UM. https://si.shimano.com/#/


Oh, being a new, you won't be able to post pics in your thread yet. But you can use the upload took still and it will go to a album that is created for you. And if you tell us you made pics, we can find them there.

the cranks move around under load... there may be an issue with the bottom bracket adjustment or bearings... the crank may have other problems too.

and there's always a chance that the frame or crank is cracked......

other than that, reset the H limit screw, since you probably changed it's setting, when you didn't need to, during a simple cable swap.
there are any large number of vids on the 'tube showing how to reset the high limit screw.
start by making sure the crank -to-spindle bolt is properly torqued, right after you make sure the crank isn't cracked or bent.
you can find proper torque specs for that bolt online.... USE A TORQUE WRENCH, rather than ham-fisting the poor thing to death, ok?

a trek 1220 is, most likely, fitted with a square taper or octalink crank set.... they require different torque specs.
do you know how to tell the difference? the crank may also have been updated to a HT2 Crank and BB

and WHATEVER you do, DO NOT just grab the FD cage and yank on it to "try and align it"... That will RUIN the derailleur.
derailleur alignment and height setting/checking is the third step to properly resetting the H screw.

Iride01 and Maddog34



I just found out I will not have a chance to continue my work on the bike until next week.

I will review the suggestions you have made and get back to you on my progress. Thank you very much for taking time out of your day to address my issue.



Mike

In the meantime, you can look up YouTube videos that demonstrate the installation/tuning procedure for that model of derailleur and shifter. (There should be model numbers on the parts that identify them.) The model of bike is probably irrelevant.

Check the frame for cracks around the bottom bracket, particularly seat tube and chainstays. With the bike on its wheels, lean it away from you and press on the bottom bracket area with your foot, looking and listening for anything that shouldn't move. Repeat from the other side. It probably isn't cracked, but this could be the cause of your problem and it's a quick and easy way to check.

The OP said that he replaced the front shifter cable because it looked a little frayed. Quite a leap from that to a cracked frame.

He says the front mech rubs under load, a common cause of rubbing things is flex, and a cause of excessive flex is frame failure. Might as well eliminate the major problems before getting down to fine tuning. It could just be that there's a bit of play in the bottom bracket, or the front high limit needs backing off a bit, or other things. But no amount of adjustment in the stand is going to achieve anything if the problem isn't adjustment.

OP said "Hello, I’m hoping to find some help with a bike front derailleur function issue. I’m working on my brother’s bike (Trek 1220 Road Bike). Just doing some general maintenance. Bike has a triple front derailleur. I completed making sure the rear derailleur was tuned well and moved onto the front. I noticed the front derailleur cable was slightly frayed at the end and decided to replace it."

You're right that it's best to eliminate major problems before getting down to fine tuning. But if the only reason for replacing the cable was that it was frayed, that likely means that the shifting was fine beforehand.

My guess (assuming the limit screw hasn't been moved) is that the inner wire is now insufficiently taut to keep the chain on the big chainring. It's easy to get the tension wrong when installing a new shifter wire, especially with a road triple crankset.

the bike is OVER-shifting now... and i doubt a pre-work test ride was conducted.
instead of arguing over details not in evidence, let's wait for a further update from spd28.

Maybe. "The chain is wanting to drop of the chainring" wording is unclear. Perhaps the OP can clarify whether the chain wants to drop to the inside or the outside.

where is the chain on the cassette when this is happening? Do you see the same behavior when on the large sprocket (crossed chain) vs on one of the smaller sprockets? If there痴 no evidence of FD chain rub, sounds like the chain is trying to derail all by itself

Thank you all for your input on this issue. Being my brother’s bike I did not spend enough time understanding what his shifting problem was. I asked to take the bike and my first encounter was that the rear derailleur was shifting lousy. I also noticed the derailleur jockey wheels were worn. I went ahead and replaced the jockey wheels and put in a new shift cable. After I had the rear derailleur shifting nicely is when I discovered the fraying of the front derailleur cable. After replacing the cable and getting the shifting working well (on the bike stand) is when I took a test ride and discovered the problem with front derailleur shifting under load. I mentioned this forum to my brother during the weekend and explained to him the problem I was having and he then told me that he had been having this problem recently. I of course did not know about this previous to my post and assumed the “having problems shifting” as nothing too concerning.

What’s occurring is this: the bike is a triple chain ring and when riding on the lowest and middle chain ring in front everything is fine. When I shift to the largest front chain ring the shift happens without issue but when I begin to pedal the chain makes lots of noise and ultimately wants to fall back to the middle front chain ring. The noise continues until I shift to the middle chain ring. I will again have some time this week to work on the bike. I will then do a better analysis of the situation. I understand the bike is old but my intent is to fix if possible. Since this is my first experience with this issue the advice is invaluable.

What do you mean by shifting under load. Load as in how much power is being applied to the pedals?

If so, then at low RPM's around 60 rpm, one will need to relax a bit on the pedaling power when shifting. The slower the crank rpm the more one has to let up on the power to let the shift occur smoothly. As crank rpms increase past 80 and more so past 90 rpm, then it takes very little to no letting up on the power going into the pedals to shift smoothly.

Again, if these are Shimano components, then go to the website I gave you previously and plug in the part numbers of the RD and FD and get their instructions for how to set them up properly. At first, some of Shimano's pictograms will seem not too helpful. But once you get to reading and seeing what the pictograms are actually showing you, you'll find them helpful.

If they are SRAM or Campagnolo, then they have instructions too. But you'll have to find them. I don't have any of their stuff any more. And Park Tools website has some good instructions and videos too. Though sometimes in the videos, Cal's antics and those of other's are a tad annoying. https://www.parktool.com/en-us/blog/repair-help

Irideo1,

when I refer to under load I’m meaning that any pushing on the pedal more than a gentle push is all it takes to cause the problem.
I did spend time looking to see if I had a crack in my frame and was not able to see anything of concern.

Today I decided to isolate my problem and remove the front derailleur. Without the front the derailleur the problem remains present. The front bottom two chain rings work well but when I put the chain on the top chain ring and begin to pedal the chain makes lots of noise and drops down to the middle chain ring. I’m happy I was able to isolate the problem but I’m still left without a remedy. The large chain ring is a 46 tooth. Is my solution simply finding a suitable replacement for that ring?

Thank you.

46 tooth ring.... dropping off the inside of the big ring... noisy, then dropping to middle ring....this sounds like a way too wide chainline issue.

what model is the crankset?
what bottom bracket width and spindle length is it mounted to?
how far from the chain stays are the inside of the pedal area of the cranks?

maddog34,The crankset is a Shimano RSX - this was original to the bike.
Sounds like a chainline issue but I’ve tried this on the smallest ring in the back and it looks well lined up with the Front top chain ring and the chain continues to fall.

Thank you.

Find out what's knocking your chain off. Since you have the bike and workdstand, you're better equipped for finding the problem than we are.You can simulate riding under load by holding back the rear wheel while working the crank on the stand. Find out what's knocking the chain off. Since it only happens on the big ring, I doubt it's the chain. Make sure the derailleur is aligned according to spec, 1-2 mm above the big ring, with the outer plate parallel to the chainrings. Check for a bent ring. Check your limit screws. Check for a bent derailleur plate. And, yeah, while you're down there, you might as well check for a bent or sticky chain. And, of course, along the way, somebody might have buggered the chain line by installing a bottom bracket that was too long.

Have you tried watching videos demonstrating the correct technique for installing/tuning that front derailleur yet? Your posts seem to point to incorrect cable tension, which would be covered in any good video on the subject.

If it were my bike, I'd shift to the smallest chainring, disconnect the cable, watch a few videos, choose the one whose info is presented most clearly, and then carefully follow the prompts, step by step.

If that doesn't take care of the problem, come back here for advice.

I have did my best to isolate the problem. In order to eliminate a variable I removed the front derailleur completely. Since the problem continues even without a front derailleur at least I have one less thing to consider. I’m thinking about taking the large chain ring off if it gives me a better vantage point to examine. It is original to the bike so I don’t know if it’s simply wear to the ring. I’ll update with more info as it comes.

Thank you for trying to help with this.



Mike

Sounds like you know what you're doing, but I have to ask: you aren't cross-chaining, are you? Would not be uncommon for, when using the largest front chain ring and the largest back cogs, for the shifting not to be great. Another consideration, I have a triple on my road bike and one thing I've found with triples is that they are very sensitive to the cage being parallel with the chainring.

I've seen bent chain rings before that had to be removed and hammered flat. Generally pretty easy to push the chain off, spin the cranks, watch the chain wheel from the front, and see if the teeth seem to gyrate side to side as it rotates. Happens when people bash it against an obstacle, I suppose.

I've also seen worn teeth on chain rings/worn chains where the chain no longer sits flat on the chain ring, but leaves a gap under it. If the chain ring's teeth look non-symmetric or sharp and worn down, that's usually a tell the chain ring has to be replaced.

For chain stretch there's cheap checker tools you just drop down on the chain and how far it drops tells you how worn out the chain is.

Could always be the crank coming lose too, though, like people have already said. The chain wheel could move outward giving poor chain line.

Then I take that it doesn't happen while you're shifting. Check the timing of the derailment. Does it always happen over e certain section of chainring or section of chain?

Hello, as I continue to troubleshoot this problem I began to look at replacement for the large chain ring. The Crank is a shimano FC-A413.
46-36-26. I've been looking online for a suitable replacement and would appreciate any assistance. I have found what looks like a match on Ebay. It is NOS but I'm not certain it is correct. Here's the link : sorry, I'm not allowed to post URL links. I search on google for this: 46 tooth chainring bolt circle diameter 110mm, an Ebay link showed the Shimano Hyperdrive Chainring SG 46t NOS New Alloy G-46 8 Spd F-46 110mm MTB LX

I'll look into this more tomorrow. Thanks.

I spoke with the seller on Ebay and he informed me that the chainring will fit my needs. I placed the order and will install when it arrives.
I'll update the group when I do.