I picked up an old mountain bike which has a triple front ring. It has 200 gs components which seem to be thumb trigger shifters. I don't know how these shifters are supposed to work but the best that I can tell is that the large thumb lever on the front derailer system moves the derailer such that it shifts from the small ring into the larger ring. It seems that this lever works much like a friction shifter and you select the ring which you want by how far you move the lever. Now for the small lever. The small lever seems to activate an indexing function which allows the derailer to move so that it shifts from a big ring into a smaller ring. At present when I am in the middle ring I can press the small lever and it drops the chain into the smaller inside ring.
Now for the problem. If I adjust the shift cable so that I can get the chain to stay in the larger ring then I can only shift down to the middle ring. If I adjust the cable so that I can shift into the small ring then I can only shift into the middle ring and not the large ring. It seems as though the shifter does not have enough throw to shift from top to bottom ring at the same time. I think that I have a shifter problem because if I hold the large lever and get the chain onto the large ring and then I release the pressure from the large lever the chain will drop onto the middle ring. Also I think that I should have two indexing triggers and I have a very weak trigger which does not move the chain from the middle ring and then I have a normal trigger which moves the chain to the lower ring.
I am probably going to take this shifter apart and try to see what is going on inside. If anyone knows what I should be checking in the shifter please let me know. If I can't get this shifter fixed I will probably go with an old friction shifter and be done with the problem.
Rans Enduro Sport, Hase Kettweisel Tandem, Merin Bear Valley beater bike
Before you start taking things apart you need to make sure that everything is properly adjusted.
Goto the Park Tool website. Find the section on front derailleur installation/adjustment. Now disconnect your shift cable completely and start at step 1 just as if you were installing the derailleur for the first time. Odds are that'll do it.
Just venting...Im sorry. Ignore now if you dont
want to hear whining
We just bought a brand new Trek 7.3 for my
wife. 10 rides later the crappo, unecassarily complicated thumb
shifters do the same thing. This is Vermont. It will take an hour to
drive 1 way to the LBS where I bought it. It took long enuff to get her
on a bike and now it doesnt work. Very frustrating.
Retro Grouch....Thank you for the parktool website tip
I am sorry to hear about the problem with the new bike. I checked park tool and then took a look inside the shifter. I did not get the shifter completely apart but I could see a wheel with teeth which is probably the problem. I am guessing that some of the teeth are stripped for the large ring setting. So unless there is some way to disassemble the shifter and rotate or replace this wheel with teeth the shifter is probably down for the count.
I can take the shifter completely apart by removing the shift cable and then I could see exactly what is going on but unless there is some way to repair shifters this would just be a waste of time.
Are you sure you are dropping the shifter all the way down to start with? Push the top shift lever twice. This should drop the derailleur all the way down. If you don't start with the shifter this way, it will make it look like the shifter doesn't have enough clicks. Now use the low limit screw to adjust where the derailleur needs to be. I usually release the cable to make sure tension doesn't cause a problem. Then take all the tension out of the cable and tighten the screw. Now push the lower lever one click. This should move the der. up to the middle chainring. Use the adjuster barrell to get this adjustment right and where the chain doesn't rub. Now push the bottom lever again. Now you should be in the top ring. If the der. doesn't move far enough, or moves to far and drops the chain, adjust the high limit screw. At this point you should be done. Push the upper lever and you should drop back into the middle chain ring. Push the upper lever again and it should drop into the small chainring.
Thanks Ray for the suggestion. When I first got the bike I did not know how the shifter worked but after some experimentation I came to the same method of operation as you described. I have noticed that when the big lever is used to shift into the largest ring that the shifter does not hold the cable tension at its fartherest point of travel. As the large lever is released the cable lets the derailer move enough that the chain will drop from the large ring to the middle ring. If I push the small lever a small down shift movement will occur which is not enough to move the chain off the middle ring. Now if I push the small lever again a positive shift will occur and the chain will move to the small ring. So my conclusion is that the rachet mechanism in the shifter has some missing teeth and the shifter will not hold the cable in the correct position to maintain the chain on the large ring.
I guess that my next step will be to totally disassemble the shifter and see if I can fix it. This will require me to remove the cable from the derailer and pull it from the shifter. This will be needed even if I decide to go with another type of shifter. Maybe I will get lucky.