Can not select big chainring

[Lightspeed]

Using Shimano Nexave ST-T400. Can select small and middle chainring but when trying to select large chainring, the selector lever moves without any 'feel' (almost like the cable is loose - but it isn't). Only at the very limit of its movement does it feel like it is moving the cable. The derailleur does move but only a very small amount and not enough to engage the front chainring. I have read the threads and watched the videos. H - L screws are all OK. cage clearance is fine. barrel adjuster is set according to videos etc. I am totally baffled. Anybody got any ideas?

[Bill]

Check for kinks, bends, or smashed sections in the cable housing. Also try putting something like tri-flow in the top end of the cable and the bottom end of the cable holding it upwards letting it drain deep into the housing. Put some tri-flow on the working parts of the Front derailler as well manually move it to see if it is "sticky".

[cyclerUK]

Can you make it work the top and middle if you adjust the cable. Or if you pull manually on the cable will the derailleur move the chain onto the big ring?

[Lightspeed]

(04-04-2010, 01:44 PM)cyclerUK Wrote:  Can you make it work the top and middle if you adjust the cable. Or if you pull manually on the cable will the derailleur move the chain onto the big ring?

Good call! yes, if I pull the cable manually, the derailleur will pull the chain to the big chainring. When I let go of the cable, the derailleur pulls back to the middle CR and the chain goes with it. I think this confirms the H screw is set OK but not why the actual shift lever will not work. The shift lever sits in the correct place but when you press it to effect the change to the big CR, it moves very freely until almost the very end of its travel before it seems to 'grip' the cable and pull it a little bit but not far enough to reach the big CR.
Thanks fo yr reply.

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(04-04-2010, 12:43 PM)Bill Wrote:  Check for kinks, bends, or smashed sections in the cable housing. Also try putting something like tri-flow in the top end of the cable and the bottom end of the cable holding it upwards letting it drain deep into the housing. Put some tri-flow on the working parts of the Front derailler as well manually move it to see if it is "sticky".

The cable is very free (have disconnected the derailleur lock bolt and can move it back /forth very easily), no kinks etc The derailleur is clean but feels very firm to move manually. I will take yr advice lube it to see if it will move more freely.

[timiji]

Since your manual manipulation of the cable gets you into the big chain ring, it may 'just' be an issue with cable tension, though I'm not familiar with the shifter you're using. First check to see if you have way too much slack in the cable when you're in your smallest ring - you might be a full gear out of sync. You can try getting rid of all the slack with the barrel adjuster ('unscrew' the adjuster to increase the cable tension), or you can loosen the cable bolt at the front derailleur and fully re-adjust the cable that way.

Sorry if you've tried all this before. Make sure the shifter (and the derailleur) is all the way to the small ring when you're checking the slack in the cable.

[DaveM]

I suspect you have a sticky pall inside the shifter. You say it moves freely at first and only seems to "grab" the cable after pushing pretty far. When you are in the middle ring and go to shift to the large, does the cable move at all as you push the shifter or does it only start moving once it feels like the shifter "grabs". Depending on what kind of shifter you have, you may be able to open it up and flush with chain lube to free up whatever is sticking. But sometime shifters just wear out.

But try to rule out any cable/limit screw adjustment issues first of course.

[Lightspeed]

(04-05-2010, 06:23 PM)DaveM Wrote:  I suspect you have a sticky pall inside the shifter. You say it moves freely at first and only seems to "grab" the cable after pushing pretty far. When you are in the middle ring and go to shift to the large, does the cable move at all as you push the shifter or does it only start moving once it feels like the shifter "grabs". Depending on what kind of shifter you have, you may be able to open it up and flush with chain lube to free up whatever is sticking. But sometime shifters just wear out.

But try to rule out any cable/limit screw adjustment issues first of course.

When on the middle CR and I try to go to the big CR, the lever moves freely (no cable movement) then 'grabs' for the last very small part of the movement. The cable and derailleur move then but not far enough to engage the big CR before the lever is at its full movement. I will see if I can degrease/flush the whole shift mechanism as you suggest. If that doesn't work, time for new shifters I guess. Thanks.

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(04-05-2010, 04:03 PM)timiji Wrote:  Since your manual manipulation of the cable gets you into the big chain ring, it may 'just' be an issue with cable tension, though I'm not familiar with the shifter you're using. First check to see if you have way too much slack in the cable when you're in your smallest ring - you might be a full gear out of sync. You can try getting rid of all the slack with the barrel adjuster ('unscrew' the adjuster to increase the cable tension), or you can loosen the cable bolt at the front derailleur and fully re-adjust the cable that way.

Sorry if you've tried all this before. Make sure the shifter (and the derailleur) is all the way to the small ring when you're checking the slack in the cable.

Thanks for yr suggestion. I feel I have done the front derailleur adjustment often enough - like about 8 times now! I have followed the instructions on this site and others to the letter. Right now, I think the shifter is wrecked somehow. Will look further into that.