RevoShift Friction: shifting to the largest gear takes a lot of force? My wife's bicycle has Shimano Revoshift shifters, and while the right (rear) one works fine, the left (front, Friction) has been problematic for a while. Originally, when we bought the bicycle, the left shifter made a clicking sound when it was turned. After a while, it stopped clicking, and since last summer, it has required tons of force to shift from the middle gear to the biggest gear.

I've tried to adjust the front derailleur (orientation, height) and the low and high limits, as well as the cable tightness, but nothing seems to remedy the force. This morning, I took the shifter apart, suspecting that something would be broken inside it, but everything seemed OK. I put it back together, but it still doesn't click and I have to use both hands to turn the lever to get it to the biggest gear.

I suspect that there's still something wrong going on in the shifter, though. If I gently pull the cable underneath the body, the shifter rotates. It shouldn't do that, should it?

The exact model is Shimano SL-RS35. Thanks for any help in advance!
Some of the revoshifts are actually friction and just don't click period, while others are pseudo-friction (they click in small increments so you can trim your shifts) - I suspect you have the latter. They are also the bargain bin parts (less than 20 dollars for a set), and thus are built with low quality and things often go wrong. Pretty much all you can do is check that the cable tension is OK, the cable isn't caught on anything and the derailleur is set up properly (If the shifter is gunked up, sometimes flushing it with WD40 helps, but thats just a temporary fix).

As suggested in this question, I recommend throwing out the RevoShift shifters if they start to cause problems and then replacing them with some other cheap shifters (maybe switch the left on a cheap thumb friction shifter, or a Shimano trigger shifter with the same number of speeds, or a SRAM Attack front shifter if you want to stick with twist).