New front thumbshifter woes

[IaninSheffield]

I've just replaced the front mech thumbshifter assembly and gear cable on my Specialized Sirrus. The problem is that, when fully connected, I can't get it to click into top gear. I've adjusted it so that the chain will shift across the three front chainrings (and stay on each), but without that click into top, the downshift obviously takes the chain back to the small ring.
The new shifter works fine across the three stops when there's no cable tension.
I've not changed the front derailleur position, nor the high & low limit settings from before the new shifter, when they were set fine.
Rear cassette and chain are relatively new.
Anyone any thoughts? Thanks.

 

[fossyant]

You might need a little more slack in the cable, or adjust the limit screw so the shifter clicks - Its a new shifter so you might need a couple of tweaks to get the click to engage.

 

[Ajax Bay]

Try resetting the top limit screw first.

 

[keithmac]

Set cable for best middle shift then set top and bottom limit screw.

As said with new bits more than likely top limit screw needs adjusting.

 

[IaninSheffield]

Thanks @fossyant @Ajax Bay & @keithmac
Have addressed my attention to the top limit screw as you've kindly suggested. Adjusting in or out didn't seem to be affecting the limit of the outward swing of the derailleur, so I took a closer look. The screw doesn't seem to come into play at all, whether I push the derailleur across manually or use the thumbshifter; the plate beneath the screw never makes contact. There's always a gap, even with the derailleur pushed as far across as it can go:

What I'm struggling with is why the thumbshifter works fine across the range ... until any tension is put onto the cable. 🤔

 

[keithmac]

Can you push the derailleur over then click into top position with the chain on the top chainring?.

 

[IaninSheffield]

Can you push the derailleur over then click into top position with the chain on the top chainring?.

Nope, no joy on that either.

Don't like being beaten, but thinking a visit to the LBS might have to be in order.