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So I've not cycled in a while but my step dad was using my bike and he has a habbit of breaking stuff. I have since decided to start cycling to work again and I replaced various parts due to rust etc (Chain, Cassette, brake pads, cables) and seeing as they didn't work properly in the first place I decided to take some time to tune the gears. Now I think I understand them but the issue I have is: On the cassette at the back the gears will happily and smoothly shift from 7 to 1 under load or not under load. But going from 1-7 it will ignore me when I switch to 2 but when I then go 2-3 it will skip over 2 and onto 3.

So the question is: Why does it work perfectly from 7-1 under any load but then under any load it will not go 1-2 but every other gear works? It's literally that 1 down to 2 that won't work.

Please take note that there is no grinding noise or anything when i flick from 1-2 it quite literally just ignores me and makes 100% no attempt to switch but it happily jumps over 2 to 3 when I flick down to 3.

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By 7-1 do you mean small cog to large or vice versa? My first guess is a cable problem. You said you replaced the cables. Is it possible you have a kink somewhere? Also did you replace housing? Did you use correct housing?Brake housing has a flat spiral wire beneath the outer plastic. Gear housing thin wires that run the length of the housing. Did you lube cable/housing before installing. Did you replace all ferrules? A missing ferrule will often cause gear housing to crush on the end and lose tension. –  vlieg Jun 25 at 13:31
    
Could be that the ramps are worn on the cassette and it shifts down fine, but won't go up very well. –  Aaron Jun 25 at 16:37

4 Answers 4

A rear derailleur moves two ways: the tension from the shifter cable will pull it one way (usually towards the larger rear cogs) and spring tension within the derailleur will pull it back when you shift down into the smaller cogs.

It sounds like the spring tension is not strong enough to overcome the cable tension / resistance when you're shifting.

If you had to replace other rusty parts, you can try oiling or just replacing the derailleur cable and housing. If those are rusty or sticky, then your derailleur spring has to pull a lot harder to get things to move.

I have also had shifting troubles when the derailleur hanger is bent, causing the mechanism to swing the wrong way when I was shifting. You can get a bike shop to check / straighten the hanger, or if you don't have a hanger (claw type derailleur) you can try to do it yourself.

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It is harder to go to a bigger (more teeth) gear as the chain is going up hill. Hyperglide helps the up hill.
The smallest gear is often loose. Not even sure you can put it on backwards. But if you could and if you did then the hyperglide would be backwards. Maybe worth checking.

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it came pre-built i simply fitted it onto the bike and then adjusted the cable. It seems to work fine going to a bigger cog or 1-3,3-4,4-5,5-6 and 6-7 all work its just 1-2 does not. the derailier makes no attempt to move. –  Dale Swire Jun 25 at 19:03
    
That is just strange that is would move down from 2-1. But not make any movement up from 1-2. Maybe try removing the chain to see is if it moves with no resistance. Lube and check cable as suggested in the comment for vlieg. Maybe something strange going on in the shifter. –  Blam Jun 25 at 19:20

I think the derailleur cable may be too loose. Try increasing the tension in the cable a tad and see if that helps. On many bikes you can increase the cable tension both at the derailleur and at the shifter using the thumbscrew.

If that doesn't help, either lube or replace the cable, and lube all the derailleur pivots.

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I had a similar issues getting into my 16 tooth gear but not coming out of it. Turns out that gear had some teeth worn down which made shifting a little sticky. After checking online and talking to a few good LBS the common answer was to swap out the cassette and chain. I had wondered if simply swapping one gear in the cassette would do it and in the end the prevailing answer is that Shimano cassettes work better as a group and by not swapping the whole thing out you are only delaying the inevitable. As for the chain, it just makes sense to put a new chain on a new cassette so that none of the nasties infect the new cassette. This might seem silly and a little OCD but I usually also take the same time to clean the BB and wipe dow the crankset with WD40. this gives my chain a few rides with that nice "new look".

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