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Old 03-27-11, 04:58 PM   #1
alanturing
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Strange Front Derailleur (Tiagra STI) Problem ... won't stay in big ring

I recently bought a lightly used, 2009 Scott CX Comp (Cyclocross) with Tiagra STI levers and a Tiagra (double) Front Derailleur. When I first got it, the front derailleur was a bit sticky when going from the large to the small ring, but I could shift between both rings.

After a few rides, I'm no longer able to shift it into the big ring. I can get the chain into the large ring, but it doesn't lock into place. It just falls back into the small ring when I let go of the shift lever. I did some experiments with cable tension by disconnecting the cable from the derailleur and holding it in my hand. When I apply very light tension, the shift lever will lock into place, but if I apply just enough tension onto the cable I get the same effect ... the lever pulls the cable but it doesn't lock into place. I tried loosening the cable on the front derailleur, but if I apply enough tension to get it into the large ring, there's so much tension that the chain goes back into the small ring. If I loosen the cable too much, it won't even go into the large ring.

I'm assuming it's either caused by an overly tight front derailleur or a problem with the front STI lever. The front derailleur seems a little stiffer than the ultegra derailleur on my road bike, but it doesn't seem outrageous. Any thoughts on something else I should check? I have an old Ultegra left shifter lying around (I bought a used pair when my road bike rear shifter broke). Should that work with a Tiagra front derailleur?
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Old 03-27-11, 05:14 PM   #2
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It's a lever problem, not a derailleur problem. The engagement in the lever is worn or gummed up with dried lube. It may be toast, but before you quit, drown it in your favorite solvent to clean and flush it, work it back and forth and see if the latching gets more positive. If so, you're in luck, clean it out, and apply some light oil and keep your fingers crossed.
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Old 03-27-11, 05:58 PM   #3
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Originally Posted by FBinNY View Post
It's a lever problem, not a derailleur problem. The engagement in the lever is worn or gummed up with dried lube. It may be toast, but before you quit, drown it in your favorite solvent to clean and flush it, work it back and forth and see if the latching gets more positive. If so, you're in luck, clean it out, and apply some light oil and keep your fingers crossed.
Probably neither a lever nor derailer problem. It's likely a cable problem. Specifically a cable housing problem. I'd suspect that the rods in the cable housing have broken loose and are not putting the correct tension on the inner cable.

alanturing: The following pictures are for a mountain bike and a rear derailer but it works the same. Shift the front derailer into the largest gear while pedaling.

Once the derailer is centered over the large ring, shift into the lowest gear on the front without pedaling.

This will release tension on the cable and allow you to pull the housing out of the frame and the shifter so that you can inspect the housing.



Look for stray wires coming out of the housing ferule which indicate the outer cable needs to be replaced.

The above method can be used for lubricating the cables too.
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Old 03-28-11, 03:37 AM   #4
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If you could send us a picture of the front derailleur it may help us resolve the issue. We are going to be taking shots in the dark here. It may just be that the front derailleur is too high (2-3mm above the large ring is suggested) or maybe rotated (not flush/parallel with the rings). Its probably a tuning problem, it takes a while to get good doing front derailleur setups. I doubt a 2009 setup has gone "bad" this quickly, probably just cable stretch.
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Old 03-28-11, 11:53 AM   #5
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You have described exactly what my left 105 lever did as well. I soaked and lubed it with no change.

A new shifter with the same cable/housing/derailleur restored the front shifting in my case.
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Old 03-28-11, 07:23 PM   #6
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Originally Posted by greyghost_6 View Post
If you could send us a picture of the front derailleur it may help us resolve the issue. We are going to be taking shots in the dark here. It may just be that the front derailleur is too high (2-3mm above the large ring is suggested) or maybe rotated (not flush/parallel with the rings). Its probably a tuning problem, it takes a while to get good doing front derailleur setups. I doubt a 2009 setup has gone "bad" this quickly, probably just cable stretch.
Here are a couple of shots of the chain in the big ring, from the side and top. Sorry for the quality ... I had to hold the lever with one hand to get it to stay, while I took the picture with the other hand




Thanks
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Old 03-28-11, 08:34 PM   #7
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I would first try shooting the shifter full of WD 40.

From the last photo it appears that the rear end of the derailleur is out too far. If you agree, try loosening the derailleur and rotating the rear toward the frame slightly. I believe the derailleur is at the correct height. Or if it appears bent you could try reshaping it in place with your hands.
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Old 03-29-11, 12:23 AM   #8
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That all looks good, maybe could be closer to the rings a little bit (lowered). Have you also made sure that the limit screws are not in too far limiting how far out it goes? Maybe they are not bottoming out too early and not allowing you to "click" or what you called "lock into place".

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Old 03-29-11, 07:48 AM   #9
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I would first try shooting the shifter full of WD 40.

From the last photo it appears that the rear end of the derailleur is out too far. If you agree, try loosening the derailleur and rotating the rear toward the frame slightly. I believe the derailleur is at the correct height. Or if it appears bent you could try reshaping it in place with your hands.
That just looks like a photo issue. It's hard to tell if the tail of the derailer is kicked out or not. Even if it were, that wouldn't be the cause of the problem. If anything, it would help since it puts the outer plate of the derailer further away from the chain. It also would not have become a problem that gets worse with time. Problems that develop over time on derailers are almost always cable issues.

Nice clean chain there, alanturing. Big
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Old 03-29-11, 10:19 AM   #10
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Problems that develop over time on derailers are almost always cable issues.
The problem may well be with the cable or housing but with STI shifters it's more often in the shifters. WD40 would be a good place to start.

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Old 03-29-11, 10:37 AM   #11
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Quote:
Originally Posted by alanturing View Post

After a few rides, I'm no longer able to shift it into the big ring. I can get the chain into the large ring, but it doesn't lock into place. It just falls back into the small ring when I let go of the shift lever. I did some experiments with cable tension by disconnecting the cable from the derailleur and holding it in my hand. When I apply very light tension, the shift lever will lock into place, but if I apply just enough tension onto the cable I get the same effect ... the lever pulls the cable but it doesn't lock into place.

The first rule of diagnostics in medicine or mechanics is the suspected problem must reflect the symptoms. The problem described is failure to latch securely into position against the FD return spring. The latching occurs in the lever and nowhere else, ergo the problem must be in the lever mechanism.

Let's apply Ockham's Razor and consider the possibilities raised.

Quote:
Originally Posted by cyccommute View Post
It's likely a cable problem. Specifically a cable housing problem. I'd suspect that the rods in the cable housing have broken loose and are not putting the correct tension on the inner cable.
It can't be cable related because degraded cables would only add friction and have nothing to do with the latching process, a loose or slack cable wouldn't enable the upshift in the first place.

Quote:
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Have you also made sure that the limit screws are not in too far limiting how far out it goes? Maybe they are not bottoming out too early and not allowing you to "click" or what you called "lock into place".
An overly tight outer limit could cause the same effect by unduly raising the required latching force, but I rule it out because that can't happen over time (limits and cables don't magically get tighter). Also an overly tight limit would make the upshift difficult difficult and OP doesn't report this.

Quote:
Originally Posted by greyghost_6 View Post
.... It may just be that the front derailleur is too high (2-3mm above the large ring is suggested) or maybe rotated (not flush/parallel with the rings). Its probably a tuning problem, it takes a while to get good doing front derailleur setups. ...
It can't be the FD itself because it does shift but won't stay there. FD issues effect the shift itself not the retention of position afterward. Also it used to work, and for the problem to manifest as described the FD return spring would need to have suddenly gotten too strong for the lever's latch, something beyond unlikely.

So we're back to the lever, which is the simplest theory which fits the symptoms as described. Either the latching mechanism is dirty, rusty or clogged with dried grease and will respond to flushing, or a pawl or detent is damaged and weakened in which the OP is SOL and needs a new lever as these are not considered repairable.
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Old 03-29-11, 11:30 AM   #12
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The first rule of diagnostics in medicine or mechanics is the suspected problem must reflect the symptoms. The problem described is failure to latch securely into position against the FD return spring. The latching occurs in the lever and nowhere else, ergo the problem must be in the lever mechanism.
The lever does indeed lock the front derailer in place. However, it doesn't do it by itself. The cables are part of the system too. If the cable is allowed to move, the shifter can't keep the cable under the proper tension and the derailer moves.

Quote:
Originally Posted by FBinNY View Post
Let's apply Ockham's Razor and consider the possibilities raised.

It can't be cable related because degraded cables would only add friction and have nothing to do with the latching process, a loose or slack cable wouldn't enable the upshift in the first place.
Indeed apply Ockham's Razor. Just know where to apply it. You are thinking about friction from the inner cable. That's not the problem. The outer cable housing is also involved. I've had exactly this problem occur with shifting and it was due to the wire bundle that makes up the compressionless housing breaking loose. The inner cable can be moved enough to shift but the inner cable won't retain tension because the outer housing wires are moving too. The outer cable may be bowing outward at some point which you really couldn't see.

At the very least, it's worth looking into before you go replacing the shifters.

Quote:
Originally Posted by FBinNY View Post
An overly tight outer limit could cause the same effect by unduly raising the required latching force, but I rule it out because that can't happen over time (limits and cables don't magically get tighter). Also an overly tight limit would make the upshift difficult difficult and OP doesn't report this.
I agree that it's not limit screw related. Everyone wants to fiddle with the limit screws but they are almost never off...unless someone fiddled with them

Quote:
Originally Posted by FBinNY View Post
It can't be the FD itself because it does shift but won't stay there. FD issues effect the shift itself not the retention of position afterward. Also it used to work, and for the problem to manifest as described the FD return spring would need to have suddenly gotten too strong for the lever's latch, something beyond unlikely.
Yep. The derailer is a robot. It just goes where it is told to go.

Quote:
Originally Posted by FBinNY View Post
So we're back to the lever, which is the simplest theory which fits the symptoms as described. Either the latching mechanism is dirty, rusty or clogged with dried grease and will respond to flushing, or a pawl or detent is damaged and weakened in which the OP is SOL and needs a new lever as these are not considered repairable.
This is where Occam's Razor cuts. Cables and cable housing are easy to check and replace. Check them first. Replace them first. If that doesn't work then move on to the shifter. Do the cheap things first before moving on to the expensive stuff.
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Old 03-29-11, 11:38 AM   #13
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Read the original description of the symptoms. It shifts fine, but won't stay shifted. Unless he has magic cables that are stiff enough to allow a shift and then somehow get too tired and stretch or sag immediately afterward it's not likely cable related.

I'm all for doing the cheapest thing first, and replacing cables is often a good place to start, but this case doesn't fit the description of a cable related problem.

He has a latching problem, the simplest theory is that he has a problem with the latch.

If my front gate keeps swinging open, I check the latch, not the hinge or the rest of the fence.

BTW- the suggested flush and re-lube of the levers (with fingers crossed) is the easiest, least expensive remedy, costing far less than a set of cables.
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Old 03-29-11, 12:18 PM   #14
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I've thought of something else the OP could try.
The Tiagra shifters are double/triple compatible and the crankset is a double. There is more than one way to setup these shifters to work with a double crankset. The standard setup is to have all of the cable out of the shifter when the derailleur is in the inside ring position. Another way to set it up is to shift up one full position before attaching the derailleur. I think this would make the big ring position the same as it would be for a triple. "I think" because I haven't done this myself but it has been discussed on this forum by others. Most Shimano triple shifters have 4 main positions for the 3 rings, plus an extra trim position for the smallest chainring. Of course it's possible that this shifter may already be set up this way, if so the OP could try the standard setup as an alternative.
It seems that Shimano is phasing out their double/triple compatible shifters. First it was Ultegra, then 105 that changed to double or triple specific shifters. Dura-Ace has always been double or triple specific.

But first I would try the WD40 flush, it can't hurt anything and it may help a lot.
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Old 03-29-11, 01:16 PM   #15
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Read the original description of the symptoms. It shifts fine, but won't stay shifted. Unless he has magic cables that are stiff enough to allow a shift and then somehow get too tired and stretch or sag immediately afterward it's not likely cable related.
Yes, I've read his original description. I've had exactly the same problem. The outer housing is a bundle of rods. I've had one or a few of the rods break loose from the plastic around them and slide. If you put tension on the outer housing and the shift will be made but it won't stay there because the rods move and allow it to shift back. Some of the rods even came out of the housing ferrule. The rods put friction on the inner cable but, as they relax and move, they allow the cable to go back to a nontensioned state and the chain comes off the chainwheel. In extreme cases, the outer wall of the cable housing will rupture.
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