Bicycle Mechanics - Set screws not functioning
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07-11-10, 04:38 PM
I tried a search of the forum, but anything with deraileur or set in it gave a lot of responses.
Anyway, the problem is that on my friends specialized dolce, with a tiagra FD it is unable to shift down to the smallest chainring. We released the derailleur cable so it would spring back and it is now possible to manually set the chain on the chainring, but it rubs the whole length of the FD cage.
The real problem is in atempting to adjust the set screws, they dont seem to do anything at all. We have tried tightening and losening the screws, but it wont move either direction. On my bike the slightest turn gives some movement so I am unsure what to do now.
Thanks for your help
07-11-10, 05:30 PM
Are you sure the "set screws" are not working ? If you do remove the cable and back off the (L) screw the dérailleur should move closer to the seat tube. It could already be there, specialized is known to run shorter BB axle which can and will cost this problem, to solve this you need a longer axle just 3 MM will do it . In other words if the axle is a 111 MM then try a 113 MM to fix it. Also make sure the dérailleur is clean , dirt can keep the dérailleur from moving.
The sure way to check the FD's limits of travel, hold the cage out and bring the inner screw in a bit. Let the spring take it in and note the position. repeat the process backing out the inner limit one turn at a time, until the FD won't move in any more. That's it's design limit and probably it's leaning on the body by now.
If that isn't inboard enough, you'll have to bring the crank out to meet it. This means either a new spindle, or swapping spacers depending on the type of BB. It isn't an entirely bad thing since most FDs are built to cover chainrings with fairly decent chainline, and if the crank is too far in you should be moving it out anyway.
07-12-10, 08:12 PM
The bike was functioning properly until recently, so it could potentially be that it is really dirty. I don't see how a longer axle would be needed because, like i said, it did shift fine.
FBinNY, I will try adjusting the inner limit screw while the cable tension is released to see what happens. I think she may plan on bringing the bike in, so I may not have any time to work on it anyway.
Thanks for your help, I'll update you if something new develops.
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