ZachB

I recently got a State 4130 Road Bike with 1x8 gearing using a Suntour R80 and indexed friction shifter. I took it out for my first ride on it and everything felt great until I tried shifting down to some smaller gears for a hill. I got most of the way up the hill and I feel the chain jump between cogs. I shift back up to a higher gear at the top of the hill and everything seems fine. When I got home, I tried adjusting the high and low screws and the barrel adjuster for the cable. I followed a park tool guide I found on YouTube to try to get it shifting smoothly. I got it so that the bike will shift from the highest gear (smallest tooth rear cog) to the lowest gear (largest rear cog) smoothly. The problem is when I try to shift the other direction the chain is skipping over cogs and jumping back and forth between them. I went through the process of trying to readjust the screws and barrel adjuster multiple times and I can only get it to shift smoothly one direction and only ever going down. I checked another guide for other problems and it mentioned checking worn parts, bent derailleur hangers, etc. but the bike is band new so I don't think that's the issue. While i was tinkering around on it, I noticed that if I shift to a higher gear and it's skipping around, I can apply some pressure on the shifter towards shifting back down a gear and it seems to fixed the jumping around of the gears. I can put it in any gear and just apply some pressure make the other direction and it makes them all smooth. Is there a way I can fix it so I can just shift smoothly both directions without having to fiddle with it? It's like the spring in the rear derailleur isn't pulling back on the shift cable hard enough is my guess, but I have no idea how to deal with this.

cyclintom

It sounds like the limit screws are set incorrectly and the friction/index levers may need to have the friction increased. If you're not an experienced bike mechanic you should probably take it to a shop since it is easy to misadjust things and drop a chain to the inside between your cogs and the wheel and cut the spokes.

ZachB

I'm at about that point. I wanted to try and fix it myself just for the joy of tinkering and learning about how bikes work. If I can't get it, I'll take it to my local bike shop and see if they can get it sorted.

veganbikes

Just FYI it is SunRace no relation to Maeda Industries the original SunTour or the new thing which also really doesn't have relations. SR Suntour.

Make sure tension is correct and make sure limit screws are set or just take it to your local shop. Also make sure not to shift under load (so like pedaling up a hill) Even really high end stuff is not so much designed for that.

ARider2

Fist make sure the hanger is not bent. This is sometimes an issue on brand new bikes.

Lombard

I'll second this.

cxwrench

Since I'm still banned from the mechanics section (and it's getting to be a bit tiresome) we'll do this here. Do the following, in this order:

1) Shift to the small cog and undo the cable from the derailleur.
2) Confirm the high limit is correct. Pedal the bike and tighten til the chain makes noise, then back it off til it doesn't plus 1/4 - 1/2 a turn. On most drivetrains you want the inside edge of the upper pulley to line up with the outside edge of the small cog.
3) Adjust the barrel adjuster on the rear derailleur all the way in, then back it out a turn or so.
4) Attach the cable, making sure the shifter is in high gear position.
5) Turn the crank and shift once to a lower gear. If you don't get any noise you're ok to continue slowly shifting to easier gears. Shift to the next to the largest cog using the shifter, then use your thumb to carefully push the derailleur the last bit to the big cog. Once it makes that shift stop pedaling and see if you can push the derailleur any further. If you can, adjust the low limit. You should end up w/ the teeth of the upper pulley centered under the teeth of the big cog. Confirm by pushing the derailleur body w/ your thumb to make sure it doesn't go into the spokes. ***If you make the first shift and you get some noise, determine which way you need to adjust by pushing lightly on the derailleur...if the noise stops you know which direction you need to turn the barrel...counter clockwise. If you push the derailleur and the chain immediately goes to the next cog you know you need to turn the barrel clockwise. ***If you get some noise and it seems to get progressively worse as you shift to bigger cogs your derailleur hanger is most likely out of alignment, bent in towards the wheel. EVERY time a bike goes in my stand at the shop with 'shifting problems', especially if it's a kid's bike, I ALWAYS eyeball the hanger from directly behind the bike first. If this is the care, align the hanger. At this point you can check the b gap adjustment. Small ring, big cog. Eyeball the gap between the upper pulley and the large cog. With your derailleur you probably want about 6mm or so clearance. Enough that when you make that last shift to the big cog you don't get any noise/the chain isn't getting pinched between the cog and the pulley. Also, you should confirm your chain is the proper length. Small ring, small cog. Chain should be just short enough it doesn't rub one the pulley cage at all. The cage should also NOT be pulled all the way forward when in the big cog. If it is either your chain is too short OR your derailleur pulley cage isn't long enough. With 1X this isn't usually a problem. If the bike is new I'd compress the housing and make sure the ferrules are seated fully by starting in the small cog, hold the derailleur body in your hand like you're trying to keep it from moving and shift back and forth 1-2 shifts with the lever. Re-adjust as necessary. This will ONLY affect housing length (NOT cable tension...that is not an adjustment, it's always the same) relative to cable length. You NEVER adjust cable tension, you are only changing the length of the housing relative to the cable.
Done.

Camilo

There's a mechanics section where you'll get great advice

cxwrench

That freakin' novel I wrote isn't great advice?

Camilo

Of course. Just being pedantic to the OP... and hoping you get back in the Mechanics good graces.