The Shimano 200GS STI is a rear mountain bike derailleur that is out of production. It is a seven-speed system that was abandoned when Shimano introduced the Sora shifter in the mid-1990s. The 200GS derailleur has only one barrel adjuster to increase tension on the cable. Shifting problems in a 200GS are almost always due to cable problems. In older mountain bikes, cables get dirty and will not travel inside their housings, causing shifter problems. To fix this, you need to clean the cable to get your bike shifting better and then tighten your derailleur barrel adjuster.
Put your bike in a bike stand. Shift the bike by hand into its smallest gear on the front and back. Reach down with one hand and pull the derailleur backwards up toward the seat as far as it will go. This will allow slack to form in the derailleur cable.
Grab the black plastic housing with the other hand where the housing leaves the derailleur. Slide your hand up the housing to where the housing stops, it should be about 10-inches from the derailleur. Pull down on the housing. This should dislodge the small, shiny bullet-like end of the cable from the ferrule. The ferrules are the small, round bullet-like receivers that are welded onto the bike's frame. Let go of the housing. The cable will go slack. Release the derailleur letting it go back into its normal position.
Trace the remaining cable up from the first housing. Locate two other housings along the length of the cable between the derailleur and the handlebars, including the one that enters the shifter. Pull all of the housings loose from the ferrules.
Spray down the entire length of the cable with the silicone spray. Move the housings up and down the cable, sliding them and spraying the cable in between the housings.
Wipe down the cable, sliding the housings up and down the cable to get all the dirt and grime out of the housings and off the cable as you wipe the cable in between the housings. When the housings slide freely up and down the cable, the cables are clean.
Pull up on the derailleur like you did the first time. Place all the bullets back into their respective receivers. Let go of the derailleur.
Turn the pedals with your hand as you reach up and shift the bike with the other hand. Watch as the chain moves up and down the gears. If the chain does not shift up to bigger gears as you shift the bike, reach down and turn the barrel adjuster counterclockwise two turns. The barrel adjuster is the serrated black knob attached to the back of your derailleur, the cable passes through the middle of it.
Turn the pedals by hand as you watch the chain. If the chain still does not move up the gears easily, turn the barrel adjuster two more times or until the chain shifts up the gears easily.
- If the cable is frayed or strands of cable are showing, clip them off with wire cutters.
- a downhill mountainbike gear wheel and gearshift mechanism image by Stephen Gibson from Fotolia.com