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Front Derailleur won't stay on big ring - tried everything

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Front Derailleur won't stay on big ring - tried everything

Old 09-06-12, 10:28 PM
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Front Derailleur won't stay on big ring - tried everything

To start, I've read dozens of threads, read instruction manuals from Shimano, Park, etc. a bunch of youtube videos, instructables, a bike repair book, and I've followed what it is pretty much the same procedure.

Now, here's the background:

My bike, with all the same components, had been working fine 2 days ago for hundreds of miles, so solutions such as "you have the wrong shifters for that derailleur" don't really make sense. I took the bike out the other day for a 30 mile ride and got rained on, it got pretty sandy and dirty so I went for an extensive cleaning. Also, while I was at it I decided to mess with my working system by cutting my cable housings shorter. I initially installed them myself over 1000 miles ago and I decided the shifter cables were a little longer than they needed to be and were blocking my headlight. I followed Sheldon Brown's recommendations for cable housing length, and cut them both down by about 5 or 6 inches. I connected them both back up and didn't mess with either derailleur besides disconnecting and reconnecting the newly shortened cables. I went out for a ride and about 5 miles in I shifted in to the large chainring and then went into the larger gears in the back so I trimmed it back, then tried to trim it up again when I went down a hill and went into the smaller gears on the rear again. At that point it felt a little tight to try to trim. When I tried to shift down to the small ring it wouldn't go in, after a little of a fight and going up and down it finally snapped in with a bit of snap.
I kept it on the big chainring for the rest of the ride and got it back home to take a look at it. My brother suggested that the reason it was working well and then suddenly changed was that perhaps the cable housing was not fully seated in the ferrule and a hard pull seated it more fully, effectively changing the cable tension.

Since then I have moved the derailleur every which way up and down, adjusted the low and high limit every which way and adjusted the cable tension from extremely loose to extremely tight and everywhere in between.

I have made the cable super loose and adjusted the limits and checked by just pulling the cable like Park suggests. I am able to engage the derailleur by pulling the cable so the chain shifts up and down with proper spacing to the cage. The problem is if I engage the shifter in most cases it will start on the small chain ring and if I pull the shifter it will go onto the big ring but not stay, like it's not pulling far enough to actually click in and stay there.

The basic problem, as I see it, is that the cable is not traveling enough to engage the click in the shifter. Now, if I disconnect the cable the shifter will pull the cable and click it in and then release it with the small lever of the shifter, which seems to indicate the shifter is working properly.

I will re-affirm that this setup WAS working before I messed with it, so I have to think it's something I did and not a broken or miss-matched component. All the guides and everything I've read and watched tell you how to adjust the derailleur but they usually brush over the actual cable tension aspect of the process, and I THINK that's what I'm doing wrong, but I'm sure it could be something else. I started off with the penny-as-spacer to set the spacing of the cage to the large chainring, from there I moved it to all different levels of spacing just to try anything I could think of. I tried adjusting the high and low stops perfectly and then way tight and way loose to try to see if I could get enough travel to get the shifter to click in.

I guess it's possible that I could have damaged the shifter but, like I said, it does click in when it's not connected to the derailleur. I do not have a barrel adjuster anywhere on this cable so all "fine tuning" has been by clamping and unclamping the inner cable and letting it out or pulling it tighter. But, despite the lack of a barrel adjuster I don't think I've made it to that point, since I can't even get it close, really.

Any opinions would be appreciated but please read first, if anyone can give me a detailed procedure for setting cable tension, I'd love to hear it. If you think this problem is related to the cable,shifter or derailleur adjustment I'd be interested to hear. If you've been through this exact issue I'd REALLY love to hear it.

Some details might help, I guess.

Shifter is Shimano 105 dual control "brifter" I think ST-5600
Derailleur is Shimano dura-ace FD-7800
Dual chainring (compact)

Thanks in advance to anyone who can offer any help.

-Jer
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Old 09-06-12, 10:40 PM
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Check the cable where it clamps on to the front derailleur mech.... it should pass over the top of the clamp bolt, not pass below the clamp bolt. Does that make sense? In other words, the cable should go from inboard of the der to up & over the arm with the clamp bolt.
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Old 09-07-12, 01:03 AM
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While the shifter and derailer are not actually compatible, I think your immediate problem is that, as you noted, the shifter isn't able to access the final click out to the big ring. Perhaps the cable is a bit too tight, or that the limit screw is also a bit too tight. The fact that you re-positioned the derailer can weigh on where the limit screw adjustment should lie.
I would also think that with the 105 derailer with a Dura-Ace shifter, the cable anchor bolt attachment ath the derailer needs to have the cable routed differently, altering the leverage so as to move the derailer cage further for the given amount of cable travel. This is well known, and the cable needs to be routed a bit closer to the arm's pivot, perhaps routed under the guide nub or possibly positioned to the other side of the bolt, depending on the vintage of the parts. (This is called alternative cable routing, and applies to all non-Dura-Ace front derailers and to pre-1997 Dura-Ace rear shifters with non-Dura-Ace rear derailers)

Note that the Dura-Ace shifter should have two clicks accesible that are both for hi gear, one being a trim position. Firstly verify that you can access both of these closely-spaced clicks with a single throw of the shifter up from the small ring position.
Also note that if the cabling is correct for this parts mis-match, that the cable should begin to slacken just as the derailer hits the lo-limit screw, not much before or after. There should not be any real cable slack with the bike shifted all the way to the small ring, just a slight lessening of the tension at most. And, the cable should almost "bottom out" against the hi-limit screw when the 2nd click clicks, with just a hair of overshift beyond the rest position after you release the lever after shifting up to the 2nd click.

Last edited by dddd; 09-07-12 at 01:10 AM.
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Old 09-07-12, 07:04 AM
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Originally Posted by Chief
Check the cable where it clamps on to the front derailleur mech.... it should pass over the top of the clamp bolt, not pass below the clamp bolt. Does that make sense? In other words, the cable should go from inboard of the der to up & over the arm with the clamp bolt.
This is a common cable routing error and would certainly explain the OP's sudden problem. The cable has to pass over the top of the little inboard tab on the fd's arm, not between it and the bolt.
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Old 09-07-12, 08:29 AM
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Thanks so much for the input so far, guys. I really appreciate it. (and the fact that your read such a long post!)

I'm attaching a picture of the cable routing, which I THINK is routed as it should be. I was hoping it wasn't as that sounded like an easy solution. I know I can bring this to the bike shop and have them do it but, besides being cheap, I really want to figure this out so next time it happens (hopefully never, but maybe on a riding companion's bike) I'll be able to deal with it. This has been totally frustrating and it will be equally rewarding to get it up and running again.



Just for reference, if I were to get a new (not too pricey) front der, what would be an ideal choice for this setup?

-Jer
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Old 09-07-12, 08:49 AM
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One possibility is that when you cut the housing, the end wasn't square and flush. I usually use a dremel tool with a cutoff disk to get the end square and flush. Another is that the cable still isn't embedded completely in the ferrule, or damage was done to the plastic outer housing that keeps the parallel strands in the gearshift cable from bulging out. Any of these things can allow the housing to effectively compress under load, which can cause the symptoms you describe...
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Old 09-07-12, 08:54 AM
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Thanks, I'll look into that to be sure but the fact that I can shift between the chainrings by hand by pulling on the cable makes it seem like it's something else. I'll take a look and make sure the ends look square and neat. Does it help to trim back just the outer plastic at all so the metal strands stand out a little proud so they are bearing against the ferrule, not the plastic, which could conceivably compress?
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Old 09-07-12, 09:13 AM
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I just cut em flush, plastic and all, and poke the inner cable through while the inner sleeve is still hot and melted. But I do bend the cables before cutting by the same amount as they would be bent when installed. If I cut the cables while they were straight, then the action of bending would leave the wires on the inner radius a little proud. I like to leave the outer plastic full length to keep all the strands aligned.

If the amount of cable pulled per click gets smaller than the system was designed for, like when some of the cable pull is taken up by housing compression, then you won't be able to get into the high or low chainring reliably, even if you can pull the cable by hand to shift the full range. At least that's what I've found... I used a brake cable housing once on about a 4" section of cable, and had just awful shifting until I replaced it with gear cable housing.

Last edited by cycle_maven; 09-07-12 at 09:20 AM.
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Old 09-07-12, 09:26 AM
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The part about cutting the cable with the housing in its approximate bent position makes a lot of sense, I think I'll try that.

For the record, this is indeed shifter cable housing.
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Old 09-07-12, 09:27 AM
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That FD is compatible with your shifter, so unless it's damaged, you don't need a new FD. The let's-try-everything approach isn't a good way to adjust a front derailleur, just follow the procedure. If you want a summary:

1. position the FD so the outer cage is about 2mm above the tallest chainring teeth, with the outer plate parallel to the chainring or a hair tail-out.

2. shift the chain to the largest rear sprocket and the small chainring, then adjust the FD's low-gear limit screw so the inner cage plate is as close to the chain as possible without actually touching it when pedaling.

3. ensure the shifter's in the small-chainring position, and that the adjuster barrel has some leeway to turn in either direction to fine-tune the cable length (say, 3 turns or so).

4. pull the cable with a bit of tension and fasten it at the FD. Your photo shows you've got the path correct, so you're good there.

5. click the shifter to the trim position for the small ring. You should see the FD move a bit. If the trim click is simply taking slack out of the cable, then use your adjuster barrel to correct that.

6. shift the shifter to the big ring, then check whether the high-gear limit screw is set appropriately. It should stop the stroke with the outer plate perhaps 1mm clear of the chain when you're in the smallest rear cog. If your shifter feels like it's straining to reach the high-gear detent, your high-gear limit screw may not be allowing the FD to swing outwards far enough.

7. after getting your FD high-limit screw set, try trimming the FD back and forth on the big ring. It should be able to do so with a relaxed feel, not like a gun going off. If it's prone to firing the chain back down to the small ring when you try to trim inwards, relax your adjuster barrel a half-turn at a time until it's mellowed out.

Last edited by mechBgon; 09-07-12 at 09:31 AM.
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Old 09-07-12, 09:49 AM
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Thanks Mech, I was actually just reading your guide on cycling visibility last night after I posted this so it is funny to hear from you!

Thanks for the rundown, and even though I've "tried it" your summary is very concise.

I think I will try it after I re-cut the housing.

in step 3 and 5 I may run into trouble because I do not have a barrel adjuster so fine tuning could be trouble, although I did get it working in the past without one! (looks like I might need to try to add one somehow)

Hopefully when I get to step 6 I'm actually able to get the chain onto the big ring.

Thanks again so much for reply and I will certainly report back.

-Jer
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Old 09-07-12, 10:04 AM
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5 or 6 inches is an awfu lot to cut off a cable housing... have you installed a shorter stem or much narrower bars since the bike was initially assembled? I doubt this is the problem you are experiencing, but if the cable housing was anywhere near the correct length before, it is almost definitely too short now.
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Old 09-07-12, 10:13 AM
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Also, the importance of the first two steps really cannot be overstated. Shaimno usually says the outer plate of the cage of the derailleur should be 1 to 3 mm above the teeth of the big ring when directly above. I have seen bikes that didn't shift right because the derialleur was 4 mm above the big ring. And as long as the derailleur is not touching the rings you can't really go too close.

And the outer cage needs to be parallel with the ring when viewed form above. MechBGone said it can be a bit tail-out, which may work sometimes, but try to get it as close to parallel as possible.
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Old 09-07-12, 10:22 AM
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It's time to go back to basics. Start by making sure the position and limits are spot on, especially the outer limit. These the limit, taking the levers out of the equation, shifting by drawing the cable away from the downtube. Make sure the limit allows for easy, crisp shifts, yet doesn't allow over shifting. I prefer a limit biased toward the outside allowing the FD to over-travel slightly and settle to the trim determined by the lever.

Now here's why FDs can be a PIA. Too long a cable, trims the cage inboard, too short jams the FD up against the limit, and can overload the lever detent. The problem is that the difference between these two can be pretty small, and difficult to manage since so many don't have any kind of fine tuning capability. I suggest that if you invest in an in-line adjuster. This will allow you to trim the FD with the same ease and precision as the rear, allowing you to dial it in and solve the rpoblem.
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Old 09-07-12, 10:28 AM
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I took the bike out the other day for a 30 mile ride and got rained on, it got pretty sandy and dirty so I went for an extensive cleaning.
Check for sandy bits in the FD under where the limiting cam meets the limit screw. Some grit in there will result in the same thing as screwing in the outer limt screw, thus restricting the FD's ability to engage to its set maximum.
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Old 09-07-12, 12:48 PM
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Originally Posted by DCB0
5 or 6 inches is an awfu lot to cut off a cable housing... have you installed a shorter stem or much narrower bars since the bike was initially assembled? I doubt this is the problem you are experiencing, but if the cable housing was anywhere near the correct length before, it is almost definitely too short now.
They were quite long because I think I left them the full factory length when I initially installed them so the left and right were overlapping by several inches in the middle, like maybe up to 6 inches. I am still able to turn the bars 90 degrees without bothering the cables so I think I'm OK. I do appreciate any suggestions or input, though.
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Old 09-07-12, 12:53 PM
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Originally Posted by FBinNY
It's time to go back to basics. Start by making sure the position and limits are spot on, especially the outer limit. These the limit, taking the levers out of the equation, shifting by drawing the cable away from the downtube. Make sure the limit allows for easy, crisp shifts, yet doesn't allow over shifting. I prefer a limit biased toward the outside allowing the FD to over-travel slightly and settle to the trim determined by the lever.

Now here's why FDs can be a PIA. Too long a cable, trims the cage inboard, too short jams the FD up against the limit, and can overload the lever detent. The problem is that the difference between these two can be pretty small, and difficult to manage since so many don't have any kind of fine tuning capability. I suggest that if you invest in an in-line adjuster. This will allow you to trim the FD with the same ease and precision as the rear, allowing you to dial it in and solve the rpoblem.
That part about overloading the lever detent interests me. Do you think it's possible I damaged the detent of the lever when i was having trouble on my ride, maybe it's good enough to engage when there's not much load on it but the spring of the derailleur is enough to make it not grab?
I tried again and I set the clearance and limits pretty well I think but it WILL NOT click to stay on the big chainring.
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Old 09-07-12, 01:03 PM
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This part from mechBgon really caught my attention:

"3. ensure the shifter is in the small-chainring position, and that the adjuster barrel has some leeway to turn in either direction to fine-tune the cable length (say, 3 turns or so)."

I myself in the past have been guilty of not ensuring that the shifter is actually in the FULL LETDOWN position BEFORE positioning and affixing.

Other than that emphasis, nothing to add really...

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Old 09-07-12, 04:40 PM
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I'm becoming more and more convinced that I actually did damage the shifter somehow when it initially wouldn't shift when I was riding. I think that the shifter can pull the cable and click in when there's no tension or little tension, but when it is has normal tension it's too much for it. When I have it hooked up and I try to shift onto the big ring I do hear a faint click around where it should be latching in but obviously it doesn't.
If it is broken or stripped or whatever, is there any fixing it or is the only fix total replacement? It seems like that may be the case from the little searching around I did.
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Old 09-07-12, 05:04 PM
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I doubt you broke it.
The downshift pawl is still working, so the pawl still does align with and hold the ratchet wheel.
That leaves the teeth on the ratchet wheel, but those won't fail from cable tension in my experience. A shifter will lock up and refuse to downshift if the cable gets latched hard against the limit screw, but frees up when the cable tension is released.

Now as for the upshift pawl, if the lever actually wouldn't actuall advance the spool to where the hi-gear clicks are, I'd say you could've damaged the upshift pawl, but you are getting the last 2 clicks.

I hope I'm not wrong about any of this, but that's my experience with these shifters. It is possible that one of the pawl pivot posts is bent however.

One last check I would definitely make is to warm up the shifter somehow, to at least 100F, then see if the pawl latching occurs with high gear.

If there is any kind of gumming involved, it is usually VERY temperature sensitive, being much worse when the shifter is cold, and also sensitive to how fast the shift is executed and released.

If heat helps matters, then the shifter needs internal oiling.

If you need a new shifter, note that the left side shifters are usually much more common to find at a good price on Ebay, because the right ones usually go bad first.

Last edited by dddd; 09-07-12 at 05:11 PM.
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