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Old 07-31-09, 12:07 PM   #1
1781ccT
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FD issues while upgrading an oldie

I'm updating my father's older '80's era Cannondale touring bike from downtube shifters to 9 speed STI.
It was originally 126mm spaced 6-speed in the rear, with a triple up front.


We've got a rear wheel with 9 speed cassette installed.
New-ish rear derailleur and rear shifter installed, and that works just fine.

Front shifter is installed, but I cannot get the original front derailleur to shift properly.
High/low limits are set properly, this was unchanged from the old setup. I did lower the FD so the outer plate of the FD is within 2mm of the large ring, and it's definitely lined up properly.
I can set the cable tension low and get it to shift back and forth between the inner ring and the middle ring - but the FD will not move enough to come close to moving the chain onto the big ring.
OR - I can set cable tension higher and go between middle ring and big ring perfectly, but no possibility of moving into the little ring.

With that said, I was able to find a *perfect* tension such that ON THE STAND, it will shift onto all three front rings, but with heavy leaning on the shift to get big ring, and only dropping the chain onto the little ring 75% of the time, which means that out on the road under real riding conditions, it will shift there less often. With this very precise tension setting, there is a LOT of chain rub when the chain is on the inner or outer ring.

SOOOOOOO.....
My questions are:
1. is this problem related to the different amount of cable pull between the downtube shifter and STI?
2. could the spacing between chainrings be different from the 6-speed era versus here in the new millenium? (this, to me, is very closely related to #1)
3. is this problem related to the movement ratio in the FD for the amount of cable pulled. (also closely related to #1)
Basically, I'm hoping that a new FD will solve the issue, but hoped somebody could shed light before throwing more and more money at it.
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Old 07-31-09, 01:11 PM   #2
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Did you try adjusting the high and low limit screws on the FD to give it more throw range?
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Old 07-31-09, 01:27 PM   #3
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The triple crank and FD were already on the bike, and they worked with the original downtube shifters. As mentioned earlier (might've gotten lost in the long post), the limit screws were already adjusted properly prior to the project.

When the cable is just hand tight, and goes just fine between the inner chainring and the middle chainring, if you try to shift from middle to outer...it literally feels like the derailleur is against the outer limit, but you can reach down along the downtube and pull the cable tighter and the FD moves the chain into the outer ring.

That's why I tightened the cable. But then with tightening the cable so that it goes onto the big ring the way it should with a "normal" shift, there's so much tension in the cable that the FD won't move inward enough to derail the chain onto the little ring.
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Old 07-31-09, 01:41 PM   #4
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What kind of front derailleur is on the bike? You said it was a touring bike so it may be mountain(ish) components. Apparently road and mountain Shimano front derailleurs use slightly different cable pull amounts, meaning an STI shifter may not shift the front derailleur properly.

Since the derailluer is original you know it has enough thrown to shift all three rings. Was the original shifter indexed or friction? Are you sure your left STI is designed for a triple?
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Old 07-31-09, 01:43 PM   #5
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You really haven't offered enough information about the components.
If Shimano or compatible you need a Shimano triple front derailleur of 7, 9, or 9-speed vintage. The chain needs to be 9-speed, preferably Shimano. The left shifter needs to be a Shimano triple compatible shifter.
Set the low-limit screw with the chain on the largest cassette cog and smallest chainring and with the derailleur cable detached.
Flip the smaller shift lever several times while pulling all slack out of the cable.
Then attach the cable to the front derailleur being very careful with the cable routing.
You should need very little if any cable tension to make it shift properly.
Shimano triple shifters have four (4) main positions plus a trim position. This effectively gives you two positions to use for trimming each chainring.

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Old 07-31-09, 07:39 PM   #6
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Shifters are 6510, which Shimano tech docs say are triple compatible
Old FD just says Shimano on it, couldn't find model information. Admittedly, I did not remove the 20-something year old part to look inside the clamp band.
Of course the chain was changed out, otherwise how could I have the rear derailleur shifting perfectly on the rear (9sp) cassette?

Crank is the original Shimano 600 triple.
Cables are brand new, Dura Ace.

Without question, the lower limit screw is adjust properly. I wrenched for 4 years.

In fact, I even went so far as to purposely back out the lower AND upper limit screws to see if that would affect the problem. It does not. The amount of cable pulled/released appears to be the limiting factor. I *can* shift it into all three front rings ON THE STAND, but it's very hesitant to drop onto the little ring under real riding. That is why I asked if the amount of cable pulled by the shifter is known to be different than previous downtube shifters, or if gear spacing up front was wider back in the day, or if the ratio of movement by the FD per given amount of cable pulled is different.
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Old 07-31-09, 07:41 PM   #7
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PS - I even considered adjusting chainline via narrower axle at the BB, but the inner ring bolts are already within 2mm of the driveside chainstay
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Old 07-31-09, 07:46 PM   #8
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Here follows my best advice for any and all problems with a front-derailleur:

Take the cable off the FD. Now install it from scratch as per Park Tool Repair:

http://www.parktool.com/repair/readhowto.asp?id=75

And BicycleTutor:

http://bicycletutor.com/adjust-front-derailer/

When you have it properly trimmed and are ready for the cable - a new one wouldn't hurt - you want to pull the cable taut - not too tight, taut. Then apply 48 to 60 inch-pounds to the pinch-bolt. Then put it through it's paces.

It's always easier and faster to install a FD from square-one, than it is to make adjustments with it already attached. This tends to fix one thing - while throwing another out of kilter. Start fresh. You'll get it.

Adding a barrel-adjuster can solve many problems with the cable coming loose - or being too tight.
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Old 08-02-09, 09:14 PM   #9
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Well, since I basically did "start from scratch" with the FD when I disconnected old cable, repositioned FD so the outer cage is within 2mm of the large ring, adjusted low limit given new chain line with the 9sp cassette, and confirmed high limit - I think that's covered. (wink wink)

There actually are barrel adjusters in place for both the front and rear derailleurs after removing the downtube shifters but the reality is, the presence of BA's does not affect my inquiry in terms of diagnostics.

If I put the "normal" amount of tension to drop the chain into the little ring (which is really just a matter of drawing out the slack by hand), the shifter won't pull cable after the middle ring - it's like I've hit the high limit, but I can physically see that the high limit screw is not in contact with the stop. Similar with the large ring...if I adjust tension such that the system properly shifts onto the large ring from the middle, but now there's too much tension to drop the chain to the little ring.

I did actually ask a couple of questions that I believe are critical to solving this issue - particularly whether the STI shifter pulls a different amount of cable compared to the downtube shifters, or whether the older FD might have a different pull/movement ratio?
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Old 08-02-09, 09:21 PM   #10
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Originally Posted by 1781ccT View Post
I did actually ask a couple of questions that I believe are critical to solving this issue - particularly whether the STI shifter pulls a different amount of cable compared to the downtube shifters, or whether the older FD might have a different pull/movement ratio?
I think the answer to both is "yes". "Mountain" derailleurs require more cable pull than "road" shifters supply. I think this is why the derailleur won't shift to the big chainring.

Could you post a picture of the existing derailleur? It would help us identify it.
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Old 08-02-09, 09:48 PM   #11
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BWAHAHA - I just wiped the thing down to take a closer look at it and it does say it's a Shimano 600 right there on the outer cage. My work area has been kinda dimly lit, but that's just no excuse!

Anyways, here's a pic of the same FD I pulled from google:
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Old 08-02-09, 10:31 PM   #12
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That derailleur looks like it is designed for a double (50-52 teeth) and would shift a triple poorly.

However, I have the same derailleur on an old 12 speed road bike and just had a look. I have to say that it does seem to have enough throw to shift a triple and it will come inboard pretty far too. Can you shift into all three gears by grabbing the cable and pulling while riding (simulating a friction shifter)? I have a feeling your problem is caused by old derailleur + new shifter, even though the 600 is a road derailleur so it should be compatible with STI.
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Old 08-02-09, 10:55 PM   #13
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Well, if I've snagged a wrong pic...my bad.


The FD that's on the bike right now was on the bike when it was originally purchased brand new, with the triple. And it definitely worked perfectly with the triple previous to this conversion.

Yes, I can actually grab the cable along the downtube and pull enough cable to move it through the entire range of motion and shift from the little ring -> middle -> large. If the cable tension is set "normally", aka hand taught or enough to pull out the slack while in little ring, I can only get it to shift from little to middle, using all available "clicks" or shifts. At this point, the shift won't pull any more cable. And at this point, I can pull the exposed cable away from the downtube to get the chain to shift onto the large ring. (see post #3)
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Old 08-03-09, 12:33 PM   #14
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Was the front shifter in its lowest position, all of the cable out of the shifter, when the cable was attached to the front derailleur? This is critical and often overlooked.
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Old 08-03-09, 12:42 PM   #15
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I'm wondering how you got a 9 spd wheelset into a 126-spaced aluminum frame?
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Old 08-03-09, 01:07 PM   #16
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I think part (or all) of the problem may be an incompatibility between the wide cage needed for a 3/32 chain and the narrower 9 sp chain that you're running now. That would mean that the FD has to travel farther to touch the narrower chain and push it onto the next chainwheel. The total travel of the FD may be correct but there is just too much 'lost motion' because of the wide cage/narrow chain misfit
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Old 08-03-09, 02:41 PM   #17
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Al1943 - yes, lowest position, all cable out

tellyho - re: aluminum frame. we're talking about going up from 126mm to 130mm, or 2mm per chain/seat stay, which is not a lot. Sheldon Brown even says it's perfectly fine. We're not cold-forming a new permanent position.

johnlyons53 - that's a reasonable theory. But it still doesn't really address how the left shifter goes through all of the shifting clicks and not be able to even come close to moving the chain onto the large ring. I suppose if I still worked at the shop, I could just swap parts and see if it would work before buying.
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Old 08-03-09, 02:45 PM   #18
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I think part (or all) of the problem may be an incompatibility between the wide cage needed for a 3/32 chain and the narrower 9 sp chain that you're running now. That would mean that the FD has to travel farther to touch the narrower chain and push it onto the next chainwheel. The total travel of the FD may be correct but there is just too much 'lost motion' because of the wide cage/narrow chain misfit

Hmm, yeah that is possible. A 9 speed chain is 6.8mm wide and an 8 speed is ~7.2 wide, those are pretty fine differences though...
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Old 08-06-09, 09:00 AM   #19
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PS - this thing was originally 3 x 6

I'm convinced more and more that it must have more to do with how much cable is pulled by the left STI shifter versus the original downtube shifter.

The shifter model number is 6510. The shifter has the appropriate number of "clicks". The documentation from Shimano indicates that it is triple compatible. That takes of shifter and whether it can handle triple.

Chain is 9sp hyperglide.

Crankset did not change. Though it could be said that slightly thinner chainrings with the newer shift ramps would smooth the process of up/down shifting, the problem has nothing to do with whether the chain balks at going up/down.

Cables are brand new. Genuine Shimano. Dura Ace, not that it should matter.

If the cable tension is set "properly" wheil the left brifter is set to the most inboard FD position, and cable movement is noted with the slightest amount of shifter movement, the farthest the derailleur moves is to the middle ring and then the shifter won't pull any more cable because it runs out of "clicks" or shift positions. The upper limit screws are set properly, so I can then pull on the shift cable where it runs exposed along the downtube, and this results in more movement from the FD, and the chain shifts onto the largest ring.

Conversely, I can set cable tension high enough to acheive a large ring shift when the left brifter makes the last shifter 'click' position. But when the other lever is pushed to downshift to middle and inner ring, the cable tension is too high to allow inward motion of the FD.

There is a very precise sweet spot that will eventually give me all three rings, with the shifter only (no pulling cable), but ONLY when the bike is in the stand. And in this very precise cable tension setting, the user really has to 'lean' on the left shifter and hold it there to upshift onto the large ring. And in order to get down to the innermost ring, the user has to either completely throw the shift from largest ring to smallest (like using momentum), or to take all the pressure off the pedals whatsoever and then pray that it'll drop. Of course, as soon as a human actually rides the bike, the chain will never drop onto the innermost ring.

Does this seem like it points toward a newer shifter, older derailleur compatibility issue?
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