Shimano SIS broken shifter

[jfilmerman]

I have an 18 speed mountain bike with shimano sis derailleur, and the left shifter will move the front derailleur, but there won't be any click into the set place. How can I fix this?

[Alex Ramon]

If the shifter still works ok, the plastic inside the shifter is likely worn down or gummed up. Try squirting some TriFlow into the shifter housing and see if it helps.

[Roger]

If you hear no click when you shift there's a good chance that the spring inside the shifter is broken. Take the shifter apart and have a look. If it's broken a bike shop might have a replacement but small items like twist-shifter springs can be hard to come by. Most bike shops don't want to bother with stocking small items like this. If you can't find one maybe you could order one from an online bike place.
How old is the bike? If it's seen better days maybe you should consider getting new and upgraded shifters. Trying to find springs just might lead you nowhere.
By the way, when you have the shifter apart, do clean it out but not with a chemical solvent like varsol. Varsol can degrade and destroy the plastic in twist-shifters and cause them to break eventually. Use a biodegradeable degreaser such as Simple Green or some other. Remember, when you regrease the inside of the shifters (do both of them) don't use a petroleum-based grease. That can do bad things to the plastic too. The best grease for grip-shifters is Jonisnnot grease and since it comes in a syringe-type applicator with a pointed tip it's easy to get into the right places. If you can't find Jonisnnot then a good synthetic bike grease will do but it's not as good as Jonisnnot which is made specifically for grip-shifters.

[DaveM]

A lot of the early SIS systems did not have indexing on the front (left) shifter. Since you have to adjust the front derailleur to stop the chain from rubbing as you move the chain around in the back, they didn't put set clicks on the front. This is mainly true of the thumb style shifters. If you have the more modern, under bar with a separate up and down lever, then ignore me and follow the advice above.

[jfilmerman]

Thanks DaveM. I think that is the case, because the bike is older. I wonder if that bothered anyone, or does it still work well like that?