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How to Adjust a Bicycle L-Screw

Learn how to adjust the L-screw from Silk Road Cycles' Brendon Nicholas in this Howcast bicycle repair and maintenance video, part two of three.


So pull it tight with your fingers. Tighten it down with your five millimeter hex wrench. And then see if it worked. So shift up.

It's shifting really smoothly up and down. If it wasn't, like if it was a little bit slow, you're going to want to make the cable tension a little higher. So you can turn this barrel adjuster to, basically to the left and what that's going to do is it's going to pull the cable tension higher. If it's not going down fast enough, then you turn it to the right. And that make a little bit more slack in the actual cable.

So now that you're up at the lowest gear, you want to make sure that you're adjusting that screw as well. That's the L screw, lowest gear. If it's not adjusted properly, let's say it's too loose, then it goes into your spokes, as you can see. That's really dangerous and you want to make sure that that doesn't happen. So we are going to tighten it down. And basically when you tighten these screws it's bringing the derailleur in towards the center. You can also push on that derailleur a little be and see if it's going to go into your spokes. It doesn't. It looks nice and straight.

There's also another screw here. It's called the B screw and basically what that does is that it allows your derailleur to sit properly on the largest cog. When you have different size cogs, that changes. That's a little bit more advanced screw there. So we'll talk about that some other time.

Okay, so going with the front derailleur, we want to make sure that the re-derailleur is on the lowest gear, the largest cog in the back. So at first what you want to do is you want to undo your cable with your five millimeter hex wrench. So your cable's off. Now you can adjust your low limit screw. And as you can see, it pushes the derailleur back and forth. So what you want to do is you want to make sure that the limit screw is set to where the chain can move freely through and making any noise, but also not too wide to where the chain could potentially fall off when shifting down.

You can see that's going to be too close. It's making a lot of noise. Back off a little bit. Give it a little bit, maybe a half a millimeter space, depending on what kind of crank you have. And then you can install your cable. So just with the back, you want to pull it tight with your fingers. Adjust it with your five millimeter.

Then you can take your back derailleur or your rear derailleur and shift it all the way down to the highest gear.

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