Front mech question

mynydd

Über Member
hi, I recently changed the cable to my tiagra front mech, as the old was was frayed and worn. And it wasn't shifting smoothly.
I now have an issue where if I drop down from the top ring, it jumps straight to the smallest ring missing the middle ring altogether. I then have to shift back up to get on to the middle ring.
I suspect I've probably fiddled around too much with the limit screws to be honest, and am not quite sure how to re start the adjustment proces.
Any ideas or suggestions would be great, thanks in advance
 
Location
Loch side.
The limit screws aren't the problem. They simply limit the maximum range of the derailer's movement. In the case of a triple, it has no effect on the middle ring.

Your problem is cable tension. Start all over again. Loosen the cable, remove the chain and confirm that the limit screws don't allow the derailer to move past the two crucial points. The FD's two blades should perfectly straddle the top and bottom rings at those respective maximum positions. Then, the outside blade of the FD should be 1mm above the highest point on the large chainring.
Now shift the shifter to the smallest chainring position and anchor the cable so that there is no slack, but also no pull in the cable. Every click should now produce one shift only, in either direction. With very cheap FDs you sometimes need a bit of slack in the low gear, but Tiagra is OK.
 
OP
mynydd

mynydd

Über Member
Thanks, that makes sense. Quite likely I've over tensioned it then.
I'll have another look after work
 

gwhite

Über Member
If you have fiddled with the limit screws, than by having the "H" screw just a little too tight means that too much force is required to place the chain on the big ring. The result is that when changing down the chain springs past the middle ring position and on to the small ring.
 
OP
mynydd

mynydd

Über Member
Many thanks, that also makes sense, as it is harder than I would like to change up to the big ring.
Will have a look at both issues later.......
 

shadow master

Well-Known Member
Cables too tight and locks the system under load on the top ring,when you release by down shifting it wants to release so much it goes straight to the bottom
 
OP
mynydd

mynydd

Über Member
Thanks all, yes it was a combination of he cable being too tight and a couple of tweeks of the limit screws, and after a lot of fiddling it's now working perfectly
 

HOU5EY

Active Member
I had the same problem recently after changing my crankset, I have done everything else on the bike myself but this time I gave in and took it to my LBS. I'm so glad I did as it only took them a few minutes and only cost £6. Would have taken me hours to get it right.
 

mrandmrspoves

Middle aged bald git.
Location
Narfuk
I had the same problem recently after changing my crankset, I have done everything else on the bike myself but this time I gave in and took it to my LBS. I'm so glad I did as it only took them a few minutes and only cost £6. Would have taken me hours to get it right.
Yes - but if you had persisted, next time you would have been able to do it much quicker..... and you could have gone to the pub for a celebratory drink and still had change in your pocket. ☺
 

HOU5EY

Active Member
Yes - but if you had persisted, next time you would have been able to do it much quicker..... and you could have gone to the pub for a celebratory drink and still had change in your pocket. ☺
You're right, it did pain me to do it especially as I had almost got it right, just a couple of mm out. But a nice feeling now I can get into every gear without a worry. Next time I'll tackle it myself, and go for the pint after. :smile:
 
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