I got a mountain bike that I bought new a few years back. I took it out a couple of times. I can count them all in one hand to be exact, but I always had problems with the shifting ever since I got it. I was pretty busy back then and put the bike away so I had it stored all this time. I finally got got it out yesterday to clean it up and lube it since it's been a long time since I used it. I did a test ride and the reasons of why I didn't use it much came back. I couldn't shift to the highest (larger sprocket) on the front of it no matter what. So I figured I try to see if I could get this fixed. I figured what's the worst I could do right? Well with a few precautions I learned and this video I found on youtube I hope it helps others too. So first things first. Watch this video first.
Now for my experience. It was a hot day and I got a really bad headache while I did this, so I'll tell you what not to do as I didn't realize this at the time.
1. I don't have a bike stand to work on this, so I flipped the bike upside down. If you need to do this to make shifting easier if you don't have a bike work stand, make sure you use a board or some towels under the handle bars and seat. I ended up scratching the bars on both sides which is not cool on a fairly new bike. I had it for a few years but it has been hardly used so it still looks fairly new. I also found out that the company didn't use any primer before the paint on the handle bars which sucks as I can now see the bare metal on the spots that touched the ground. There is just no primer under the pain at all, it's all nice and shiny.
2. With that in mind. I found that the best thing to do to check where the middle of the adjustment screw on the handle bar was, was to put the chain in the smallest gear up front. Leave the rear in the 5th or middle gear all the time to make life easier. You should be able to go into all three gears up front with the back in the middle.
3. Once you find the middle, leave it there and take loosen the cable to the derailleur. I found I could turn my adjusting know about 30 times. Every flick of my thumb and index finger was counted as one. This is just how I did it on mine since there are no marks unless you make them and I didn't want to do this. It works just fine.
4. Now, my bike was not shifting up to the high gear (the largest sprocket). I found out that I could put the screw driver in between the derailleur right in the middle to help me move it out past the large sprocket instead of between the tire. I think it's safer here, but it may depend on whether the bike has the space too. I then tighten the cable and was then able to go into this gear. Unfortunately I found my chain would come off. Meaning when I shifted I could move the derailleur out that far which was too much. Not what you want. This is where the adjustment screw comes in.
5. I forgot to mention the two screws on the derailleur. I found out you can play with these all day long and it won't make a difference until the derailleur is mechanically set correctly. So for now I actually unscrewed them all the way out and it made no difference. I just left them here to make my life easier.
6. When I would pull the derailleur out, I found out mine was too low. Now this is checked with the largest sprocket which also means the chain had to be on the largest sprocket in order to move this far. You can move the chain into the large sprocket with your hands so don't worry about it. I then was able to check the height which I needed to fix. Make sure to check this without the cable tension or your derailleur will just flip on you. Ask me how I know. You also only need to loosen it just enough to let you move it or it will just slide all over the place. It's hard to adjust and pull it at the same time to check the height so this is why you don't want it too lose.
7. Once I got the height correctly and made sure it was parallel to the sprocket. I tighten it up. I then pulled it enough to just clear the sprocket so that the chain had space to go into it. This is when you get the cable and pull it so that it only pulls that far out. You can go further but that will also take out the chain. So tighten up the screw for the cable and check by going through the gears to make sure you can actually get into all three if you have three sprockets like I did.
8. If all is well, now it's the time to adjust the high and low gear screws. As the video says, these are only limit screws to prevent the chain from coming out of the sprockets on each side. While on the low gear, turn the low screw to just give the derailleur enough space to clean the chain. That is all you need there. So don't use these as your main adjusting screws or you will be pulling your hair out. I adjusted these last and left them alone. Even if these are not correctly adjusted, as long as you have the derailleur mechanically adjusted, you can fix these without much fuss any time by moving the chain to the highest and lowest gear. That's what they are for.
9. Move the the chain to the large gear and do the same. This is where that handle bar adjustment will come in now. Once you got all the mechanical stuff done, you just use the thumb adjustment to allow the derailleur to move out only enough to go into the large sprocket. This will take some trial and error. I ended up riding the bike up and down my street until I was able to get into all three gears without too much fuss. It still takes a bit to get into the gears but I think it's more of my inexperience and maybe a tiny bit more high screw adjustment.
So that's pretty much it. I'm typing this with my sore fingers because getting to that thumb adjustment screw can be a pain depending on what gear you're on. I also wanted to make sure I wrote this today since I just finished getting this set up this morning. I started yesterday and that was just a bad day. So it's now done. Unfortunately for me, this is how the bike shop I bought if from tuned. I always had problems shifting from day one and finally took a look at this now and just wanted to get it fixed. So if you ever buy a new bicycle and have problems, take it back and get them to check it for you. Just make sure you understand how to shift before you do too or you'll just be wasting time as it does take some learning to do this correctly.
On a side note. I tried other gears and videos I saw online and this one was the one that actually got me closer to what I needed to do so this is why I recommend it. Yes it does take some doing, but it does work, you just be patient. Trust me I know, I almost gave up but just figured what's the worst I could do if it wasn't already working. Okay I ended up scratching the handle bars and hate myself for it, but I had a pretty bad headache so that was the last thing I was thinking of yesterday while I was trying to get it fixed. It's the middle of summer here so the heat didn't help any. Anyway this should also work for any bicycle and I also learned how to tune my own bicycle derailleur.