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Fixing Triban RC120 gears - locked down in Italy

Hi,

Im locked down in Italy and all the bike shops are shut, so I’m having to learn quickly how to fix stuff myself and am a complete novice. Would appreciate some advice about a very specific problem I’m having.

My new bike was having problems with the gears - shifting up and down and also catching on the front derailleur. I ordered it online so have a feeling it wasnt serviced before they sent it out.

I tried to fix this by following various online videos, particularly focused on high/low settings for the derailleurs, the cable tension, indexing etc.

Now it shifts down gears pretty smoothly but when im in the lowest gear at the rear/biggest sprocket, when I shift up it jumps 3 or four gears, so its just 2 clicks from lowest to highest, when there are 7 gears.

I’ve tried fiddling with the tension indexing etc, but its no good.

Any suggestions as to what the problem might be and how to fix it? I’d really like to be able to use the bike for a bit of exercise, but at the moment its basically unusable unless i stay in top or bottom gear.

Cheers

Dan

Posts

  • I'd make sure everything is moving smoothly. Lube the derailleurs and make sure the cables are moving freely and not bent or caught in anyway. Make sure the rear wheel is full inserted into the dropouts. You said 7 speed but isn't it a 8 speed cassette on the back?

    The dual derailleur setup is a rubbish engineering solution in my opinion. Remember you don't do small to small or big to big on the cogs if the front derailleur is touching the chain in those that is pretty normal i.e. 52F > 34R or 34F > 11R because the chain line is so extreme. A 16 speed bike doesn't really have 16 gears, you can probably eliminate 4 of those gears that you shouldn't be using. I only write that as I've seen people complain about the the front derailleur touching the chain but they were using an extreme angled chain line.

    I'm unsure about how good Microshift groupsets are but Decathlon would have fitted them because they are cheaper than Claris. Personally I'd much rather have Claris. I do have a folding bike with a Microshift 8 speed rear derailleur and its not great but to be honest being a folding bike with 20" wheels the derailleur can easily get caked in mud and censored from the road so it would probably be unfair to judge it. In my limited experience I would consider Microshift derailleurs more equal to the higher end Tourneys than Claris.
  • arlowoodarlowood Posts: 2,538
    edited March 2020
    It sounds as if you have too much tension in the rear derailleur cable/spring.

    The null point or "rest point" for the derailleur cage is the smallest sprocket (highest gear). In the set up videos for indexing you should normally have been advised that with the chain on the big ring at the front, click your rear shifter all the way so that it is in the highest gear (smallest sprocket). Loosen the cable at the rear derailleur and wind the barrel adjuster clockwise to release all the tension. To index the gears you then need reattach the cable and click your shifter once as if you were changing to the second smallest sprocket. You then apply tension to the cable with the barrel adjuster at the rear derailleur so that the cage eventually moves over to shift the chain onto the second smallest cog. Turn the barrel adjuster a further quarter turn and then check that the down-shifting (moving to larger cogs across the cassette) is smooth.

    From what you describe it appears that to get your down-shifting to work you have had to wind the barrel adjuster too far and created too much tension on the spring that moves the derailleur cage. Because of that, the chain is being whipped across the cassette rather than doing a more measured single switch to a smaller cog.

    It sounds like the cause may be due to poor cable routing or a particular pinch point in the routing of the rear cable. This will restrict the smooth movement of the inner cable and lead to having to put too much tension on the cable to get the indexing to work initially.

    Try detaching the cable from the derailleur and if you can access the shifter end of the cable, try pulling it back and forward to see if you can feel any resistance. Try lubing the inner cable where you can get at it and also examine the routing to see if there are obvious kinks or sharp bends that might be the issue.
  • Thanks Arlowood. Really helpful and clear. I tried releasing tension/unwinding barrel adjustors/indexing again. Lubed up the cable which seems to be moving fine and with no obvious kinks. It’s a new bike so wouldnt really expect that anyway.

    Still the same problem. Gears shift down (small to large sprocket) pretty much fine. But when i come back up (large to small) it jumps straight from the largest sprocket to the smallest.

    The front derailleur is rubbing a bit and frankly was the reason I started fiddling with it in the first place but this feels like its got more to do with the tension in the spring in the rear derailleur.

    Any other ideas?
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