Hello everyone! I've recently purchased my first road bike, a Trek 1500, with shimano st-5510 shifters. Everything was going great but noticed that the left shifter was having an issue moving the front derailleur from the second chainring to the 3rd, so I figured that the front derailleur cable just needed to be tightened a bit. Tightened the cable and bit and give it another shot. Had no issue going from the 1st to second chainring, but when shifting to the third, the shifter lever was really stiff, so I stupidly pushed it pretty hard and heard a pop. Now I can still shift in and out of the 1st and 2nd chainring no problem, but when trying to shift into the third, the shifter just clicks and does not pull the cable. My gut tells me that the shifter is shot and will need replacement. Is there a possibly that the issue could be elsewhere or the shifter repaired? Now, I've tried to source a replacement st-5510 triple shifter, but have had no luck. I am though, able to find a st-5603 triple shifter, I feel that it should work just fine, but I have a few concerns. It seems that the 5603 shifter is meant to only work with a 10 speed cassette, but mine is a 9. I don't think it should be an issue though , since we're talking about the front shifter and not the rear, or am I mistaken? Thanks in advance for any help!

Front shifter will work. Any road triple front shifter.

Back to the original problem for future reference.
The "H" limit screw was/is probably in a bit too far, preventing the FD from swinging out far enough. Unscrew it 1/2 turn at a time and retest.

The limit screws "Low" and "Hi" need to be set correctly first.

Thanks a lot for the replies guys. And good point about the limit screws, just wish I knew about them sooner haha. This is my first "real" bike, so i still have a lot of learning to do. I'll go ahead and order the st-5603 shifter then!

So another question has come to mind. I've ordered the 5603 shifter, will that be compatible with my current derailer, which is an fd-5504? Or will I need to replace that with a 5600 series derailer? Thanks again for any help! I've never serviced a bike before, other than changing tires, so I'm learning as I go here. I know I could just take it to a local bike shop, but I'd much prefer to learn how to work on them myself.

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Well Slaninar, thanks for the input I guess. Just looking to make sure I'm going about this the right way, and fully equipped to tackle this repair without running into further issues. This may seem like a basic question to some, but everyone has to start somewhere.

Loads of good info on the Net. Both youtube videos and sites. As far as compatibility goes, some detailed explanation from my blog:

6) Compatibility - front shifters - Cycle Gremlin

5) Compatibility - front derailleurs - Cycle Gremlin