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Old 02-08-09, 08:49 PM   #1
thirdin77
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won't shift into small ring

I've got a 09 Specialized Tricross Sport which came set up like so:
  • 50/39/30 JIS (square taper) crankset
  • 68x103 JIS bottom bracket
  • Tiagra triple front derailleur
  • 11-34 cassette
  • Deore LX long cage rear derailleur

I changed the crankset and cassette so that it is set up like so:
  • 46/34/24 Stronglight Impact JIS crankset
  • 68x110mm JIS bottom bracket (Stronglight recommends a 110mm-width bb)
  • (original) Tiagra triple front derailleur
  • Sram 12-26 cassette
  • (original) Deore LX long cage rear derailleur
I installed the bottom bracket and crank arms per the instructions on bicycletutor.com, including tightening the bb's drive side to 300-350 in lbs and torquing both crank arms to 420 in lbs. I used a Park TW-2 torque wrench.

I adjusted the front derailleur per the Tiagra triple derailleur instructions, setting height 1-2mm above the big ring, setting the rotation parallel to the rings, setting the stops correctly and setting the tension to allow me to trim in the middle ring.

The set-up allowed me to shift into all cogs from the middle ring and shift easily into the big or small ring, without dropping the chain off of the big or small ring. I test rode it shifting into any combination I could think of and it worked great.

Then, early into my ride the other day, I shifted from my middle to my small ring at the base of a hill, crested the hill and shifted back into my middle, and at the beginning of the next hill, when I shifted my derailleur to my small ring position, the chain just wouldn't derail onto my small ring; it would just rub against the front derailleur but not shift.

I tried adjusting my low stop but it's let out all the way and when I manually place the chain onto the small ring, with the derailleur in the small ring position, the chain is perfectly centered between the sides of the derailleur cage.

I tried adjusting my cable tension but that produced no effect.

My front derailleur's height looks great, 1-2mm above the big ring when shifted into the big ring.

I can still shift between the big and middle rings and trim the middle ring.

Again, it was working and then it spontaneously decided to stop working. I'm all ears, or eyes, I guess.

Last edited by thirdin77; 02-08-09 at 08:53 PM.
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Old 02-08-09, 10:02 PM   #2
Panthers007
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First thing I'd look at would be the cable-tension. Physically, if needed, move the chain onto the small chainring, and the largest rear cog of the cassette - your lowest gear. Now check the cable. Is it really tight? If so, release the cable-anchor bolt and give it a bit of slack. It should still be tight - but not very. There should be no bends in the cable and it should have resistance to being pushed. But not tight like it was under load in high-gears.

You are the second person in as many days to have this problem. Might be a virus?

EDIT: Work carefully on the anchor bolt. They tend to be alloy and will strip if one applies high torque. It's an acquired touch to know how much torque to apply. I never did it with a Park Tool TW-2 though. I'll check that sometime.
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Old 02-09-09, 03:41 PM   #3
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Adjust height of derailleur and angle of cage to get closer to small ring...keep trying. A longer bottom bracket (3-5mm) would bring the small ring out more.
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Old 02-09-09, 04:23 PM   #4
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If it worked before and not now and you didn't change anything, something moved or seated or got bent etc.

If everything is as it should be, disconnect the cable and tighten the low stop until the chain shifts into the middle ring.
With the chain on a middle-ish cog, turn the cranks and loosen the low stop until the chain falls onto the small ring.
If it won't go, try on a big cog.
If it still won't go, you can try rotating the der. just a hair clockwise looking down on it from the riders position.
If it still doesn't work (obviously you're gonna have to adjust everything else after you get the little ring to work), the chainline is probably wrong or the der. doesn't like that crankset.
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Old 03-01-09, 04:37 PM   #5
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Well, to follow up and so that others can use this thread as a reference, I did replace the 110mm bottom bracket with a 113 and now it'll shift into the small ring.

With the 110mm bb, I had tried adjusting the cable tension and the front derailleur rotation, both to no avail.

While inspecting the set-up as as whole, though, noted that my low stop screw was almost all the way out and that letting it out any more would let the derailleur hit the seat tube. As well, my high stop screw was almost all the way in.

Given the above, it seemed obvious that the crankset was situated too far inboard so it needed to come farther outboard- but how far? To find out, I loosened my high stop screw all the way and noted that there was about 3-3.5mm clearance between the chain and the outer cage fo the front derailleur so that was how much wider my bb could be while still being compatible with my Tiagra front derailleur.

That being, I chose to upsize by a small increment, from a 110 to 113, understanding that I could get 1.5mm more width on the drive side.

After installing the 113, I can adjust the front derailleur's low stop such that the chain doesn't rub when I'm in my small ring/big cog combination and there's still enough clearance between my front der and my seat tube.

On my test ride, shifting was mostly fine except the chain would sometimes kink- like it was being folded into an s-shape- when I shifted from my small to my middle ring so that's the next fun problem to work with.

Coincidentally, my Park chain checker says my chain is stretched to .75", though it's a nearly-new HG73 chain. Also, I did exceed my front derailleur's manufacturer-stated capacity of 20T as I'm running a 22T capacity. So I guess I can reduce the capacity/small ring or change the chain if troubleshooting and tuning fails.
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Old 03-01-09, 05:02 PM   #6
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Quote:
Originally Posted by thirdin77 View Post
Well, to follow up and so that others can use this thread as a reference, I did replace the 110mm bottom bracket with a 113 and now it'll shift into the small ring.

With the 110mm bb, I had tried adjusting the cable tension and the front derailleur rotation, both to no avail.

While inspecting the set-up as as whole, though, noted that my low stop screw was almost all the way out and that letting it out any more would let the derailleur hit the seat tube. As well, my high stop screw was almost all the way in.

Given the above, it seemed obvious that the crankset was situated too far inboard so it needed to come farther outboard- but how far? To find out, I loosened my high stop screw all the way and noted that there was about 3-3.5mm clearance between the chain and the outer cage fo the front derailleur so that was how much wider my bb could be while still being compatible with my Tiagra front derailleur.

That being, I chose to upsize by a small increment, from a 110 to 113, understanding that I could get 1.5mm more width on the drive side.

After installing the 113, I can adjust the front derailleur's low stop such that the chain doesn't rub when I'm in my small ring/big cog combination and there's still enough clearance between my front der and my seat tube.

On my test ride, shifting was mostly fine except the chain would sometimes kink- like it was being folded into an s-shape- when I shifted from my small to my middle ring so that's the next fun problem to work with.

Coincidentally, my Park chain checker says my chain is stretched to .75", though it's a nearly-new HG73 chain. Also, I did exceed my front derailleur's manufacturer-stated capacity of 20T as I'm running a 22T capacity. So I guess I can reduce the capacity/small ring or change the chain if troubleshooting and tuning fails.
Just by visual inspection with the middle chainring lasering to the middle of the cogset - was it off?
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Old 03-01-09, 05:29 PM   #7
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Just by visual inspection with the middle chainring lasering to the middle of the cogset - was it off?
When I had the 110mm bb, I never did ascertain the chain's straightness when I was in the middle/middle, nor did I measure via Parktool.com's instructions for measuring chainline. I probably should.

In the times that I've been riding and looked down and seen my chain in the middle/middle, though, it looked straight.

What did you have in mind when you asked? That I should measure my chainline as a criterion for choosing my bb width? To see if I should change to a 115mm bb? I'm open to input.
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Old 03-01-09, 10:50 PM   #8
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My rule of thumb for front derailleurs, after height and adjustment, is to set the limit screws. At first the outer is set to keep the chain from dropping between the large ring and the crank. The inner is set to just clear the chain in its innermost position. Then, starting with a quite slack front cable, I progressively take in cable until I can hit the middle ring consistently. For Shimano and SRAM triples this means the cable stays somewhat slack when on the inner ring.

Only after being able to hit the middle ring from all rear cogs do I start to work on hitting the outer ring, and that involves working mostly with the limit screw and fine-tuning the cable tension.

Sometimes, when a fat seat tub will prevent the front cage from getting in close enough, I cheat a little by rotating the derailleur so the rear of the cage turns in a smidge.
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