Front mech: can't get into 3rd ring !

[NigelA]

Re: Front mech.
Have fitted a replacement Shimano front groupset 3 chain wheel selector (SHIMANO SIS LEFT THUMB Bike SHIFTER SL-TY31) because the previous one was broken. The issue is that small and medium wheel can be selected but for the large wheel the selector just jumps back to position two. The stop adjustment screw at the mech is right out, so that won't be getting in the way. The inference is that the tension is too great meaning the 3rd wheel position on the selection can not hold it's position and so it jumps back to position two. The starting point for setting up was to have the selector in position one and the cable dis-connected at the anchor point on the mech, meaning the mech was in position over the smallest wheel, then pull the cable take up the slack and secure it. Originally, the adjuster at the selector was screwed fully in. Thanks in advance for any helpful advice.

 

[boydj]

Your front mech is not getting quite far enough out for the chain to stay on the large chainwheel. This means either there is not enough tension on the cable when the chain is on the small chainring (most likely), or the low adjustment screw is slightly too far in, so the starting point of the mech is too far inboard. There's a lot of trial and error with a triple in getting the front mech just right and sometimes just a very minor adjustment is all it takes.

 

[NigelA]

Many thanks, boydj, much appreciated. Will try that.

 

[NigelA]

The selector will go to position three (for the largest chain ring) and will select the large ring, but it seems the return spring on the mech is so strong that the click stop on the selector can not hold it there and it flicks back to position two. So, not contradicting you, boydj, but I think it is not a matter of adjustment as such but how to reduce, if possible, the return spring tension on the derailleur.

 

[boydj]

There's no way to reduce the spring tension on the derailleur, other than by adjusting the cable, assuming that the positioning of the mech is correctly adjusted (this is important).

I've changed the front mech on my triple, or taken it off to clean it multiple times. Getting it correctly adjusted is fiddly, but a bit of patience gets me there. The 'L' screw needs to be where the chain just gets pushed off the middle ring and no more, and the tension on the cable when the chain is on the small ring should be not too tight, so that it can get to the big ring easily with not too much pressure on the cable.

I've done this on both Campag and Shimano bikes. Campag is easier, because the shifter has multiple stops. I can remember a lot of frustration the first couple of times I did it because there is a learning curve. Stick with it.

 

[Ajax Bay]

Getting [the FD ona triple] correctly adjusted is fiddly, but a bit of patience gets me there.

This ^^. Especially if you haven't got an effective in-line adjuster. Experience is no substitute for (ETA: persistence and) patience, and the odd deep breath or three.

 

[NigelA]

Many thanks, boydj and Ajax Bay. Will follow your advices. Thanks again.