What do the screws do on a rear derailleur?

Asked by: Scott Lefebvre

Derailleurs are fitted with limit screws that stop the derailleur from moving too far inward or too far outward. If you look closely as the derailleur moves, you can see the limit screws stopping the derailleur at each end of it’s travel.

What does each screw on a derailleur do?

Your derailleur has two limit screws. For the outer limit, you adjust the H-Screw, so your chain does not fall between the cog and the dropout and for the inner limit, you turn the L-Screw, keeping the chain from derailing towards the spokes.

What are the three screws for on derailleur?

On most derailleurs there are three limit screws: the upper limit, Lower limit, and B-limit. The upper limit screw sets the maximum distance the derailleur can shift in high gears. The lower limit screw sets the maximum distance the derailleur can shift in the lower gears.

What is the third screw on a rear derailleur?

B-Tension

B-Tension is an adjustment using that mysterious third screw on the back of your rear derailleur. Its proper adjustment is the final step to clean and quiet shifting. It also provides a degree of chain tension assuming: Chain is properly installed and the right length.

How do I adjust the tension on my rear derailleur?

So what you want to do is first shift your bike into the smallest gear releasing all of the cable tension. And you'll feel that it's quite loose. Here. Once you've done that.

What does the low limit screw on a rear derailleur prevent?

If you look closely as the derailleur moves, you can see the limit screws stopping the derailleur at each end of it’s travel. The main purpose for the limit screw is to prevent the chain from going into the spokes or into the frame.

Why is my derailleur hitting my spokes?

Often, the derailleur hits the spokes when its hanger is bent following a heavy hit. If that’s not the case, it could be due to wobbly spokes, misadjusted limit screws, or incorrect cable tension.

Why does my rear derailleur slip?

Most of the time, a skipping chain is caused by cable stretch. In the first half dozen rides on a new bike your shift cables stretch the most. They can also stretch over time as you ride. Hippley explains, “It takes cable tension to open a derailleur, which shifts your chain between gears.

How do you fix a derailleur skipping?

Now one of the most common causes is simple derailleur adjustment on modern derailers with index shifting. The pulleys in the cage. Here should line up with the cog that the chain is on.

Where is the B tension screw?

The G is the guide pulley it guides our chain across the cassette B is for the B set screw that's the body angle screw that helps position the guide pulley close to the cogs.

How does B screw affect shifting?

You may experience poor shifting performance before adjusting the B smooth shift to the smallest chainring.

Why is my derailleur touching my cassette?

When the spring breaks or wears down, the derailleur becomes “weak”, and the chain pulls it forward too much. In some cases, the derailleur assumes an awkward position causing rubbing against the cassette. If you have a bad derailleur spring, the solution is to replace it or buy a new derailleur.

How does B tension screw work?

Simply put, the B-Tension screw is there to control the gap between guide pulley (the upper pulley on the derailleur) and the bottom of the cogs.

How do I adjust my Shimano rear derailleur?

The derailleur down into the small cog. Once we do that we're going to turn the barrel adjuster all the way in so that we have room to adjust it. After adjusting the cable position at the anchor.

How do you adjust the tension on a derailleur chain?

The barrel adjuster on the rear of the derailleur controls cable tension turn it one turn clockwise.

How do you adjust the tension on a derailleur cable?

Adjust the cable tension



Turning the adjuster anticlockwise increases tension on the cable, bringing the derailleur closer to the wheel. Clockwise decreases the tension, moving it back towards the frame. If the chain seems hesitant to shift up, increase the cable tension by turning the barrel adjuster anticlockwise.

How do you tighten a rear gear cable?

For a second and then comes back down it means the cable is too loose so the best way to adjust it is to take this adjustment knob here which adjusts the cable tension. And turn it out a few turns

How do I calibrate my bike gears?

Keep it as close to that as possible and that also allows then for the chain to move its maximum range at the back there to give it hopefully.

Do derailleur springs wear out?

That said, derailleur springs will lose tension overtime, and pivots will get sloppier. Shifters can wear out too (if you ride enough), and most cannot be serviced back to health. But before you go sinking money into these more expensive components, best try a new cable/housing or get a second opinion.

How long will rear derailleur last?

Derailleurs will last almost indefinitely. The jockey wheels will wear out in time (tens of thousands of km) but the rest of the mechanism shouldn’t see significant wear. It could be that the spring will break at some point due to material fatigue, but that is also a relatively easy to replace part on most derailleurs.

How do I know if my rear derailleur is worn out?

Worn Derailleur



All derailleurs wear out at some point. Check for wear by pulling laterally on the lower cage. Compare this movement in the linkage of a new derailleur. Sloppy pivot and linkages will produce inconsistent shifting, and the only solution is a new derailleur.