The limit screws do not control the derailleur on the sprockets between the two extremes. These are set using the barrel adjuster and tension on the inner wire. The limit screws are usually marked "H" and "L". The "H" controls the outer most limit of the derailleur, and the "L" controls the inner most limit.
What do the H and L screws do on a derailleur?
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 does H and L mean on a derailleur?
You need to adjust the high (H) and low (L) limit screws on the derailleur. Viewed from behind the bike, the H screw limits how far the derailleur can move to the right, while the L screw limits how far the derailleur can move to the left.
What are the three screws on a rear 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 does the B-tension screw do on a rear derailleur?
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.
34 related questions foundWhat is AB screw?
Type AB: Found on Sheet Metal (Tapping) Screws. Type AB tapping screws have spaced threads and gimlet points. Like the Type A, they are used in thin metal, resinous plywood, and various composite boards. Type AB screws offer a wider range of applications over Type A screws.
What size are Shimano limit screws?
Based on the sizes listed on a couple of Shimano rear derailleurs, the limit screws (Shimano calls these "Stroke Adjusting Screws") are metric machine screws. Specifically, M4 x around 18 mm.
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.
How do you adjust a derailleur limit screw?
Set the limit screws
With the gear cable disconnected, gently pedal forwards until the chain drops onto the smallest sprocket. Find the screw towards the back of the derailleur marked H (for high). This is typically a cross-head, but some derailleurs use hex-head screws instead.
How do I know what derailleur I need?
If you are replacing an existing derailleur on a bike, simply count the number of cogs on your cassette and you're good to go. If your drivetrain's speed is an unknown quantity, you can count the number of steps that your shifter runs through and add 'one' to determine the number of gears your drivetrain has.
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.
Why is my derailleur hitting 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 do you know if you have a bent derailleur hanger?
Rotate the arm of the alignment tool to the 12 o'clock position (pointing straight up). If your hanger is straight, the gauge arm should sit in the same position relative to the rim. If it's not straight, this will indicate the direction in which the hanger is bent.
What is a rear derailleur?
The rear derailleur is the mechanism that shifts the chain at the rear sprockets. There are many different models but they all share the same basic design and functionality. Derailleurs are secured to the bike with a mounting bolt to the frame's derailleur hanger.
What size is derailleur B screw?
The B-screw is an M4 x . 75 pitch x 12mm length. Looking at a couple older shimano derailleur's, it appears that the B-screw is also an M4.
What is derailleur B screw?
The B-gap or B-tension screw is located at the very back of your derailleur. It pushes against a tab on your frame's derailleur hanger, allowing you to adjust the distance between your rear derailleur's top pulley and the cassette. That distance is your B-gap.
What are Type 17 screws?
The Type 17 Screw has a course tapping thread and a special long sharp fluted point to capture chips in timber.
What are Type A screws?
Type A: Type A screws have coarse threads that make them useful when you need to drill or nest a hole in thin sheet metal, resin plywood, asbestos combinations and other materials. They are threading screws and not recommended for new designs.
How do you move the rear derailleur outwards?
When adjusting limit screws, tightening (clockwise) the screws will always restrict movement of the chain outward and loosening the limit screw (counterclockwise) will allow the chain to move farther outward toward the spokes or dropout. The low limit prevents the derailleur moving in toward the spokes.
How long should a 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.
