Thursday, September 2, 2010

How-To: Adjust rear derailleur limit screws

What the heck are all these screws for???!

Limit screws are very crucial to the proper operation and longevity of your sensitive and expensive parts. They are located on your front and rear derailleurs. Here we will deal with the limit screws on your rear derailleur.
These guys are super easy to adjust and are yet another 5 minute job once you get the hang of it. This How-To assumes that all other adjustments are in spec (cable tension, b-tension, hanger alignment, friction free housing/cable). Of course once you get more familiar with how everything works in harmony you will be able to switch around between all of these adjustments since one adjustment usually affects the other. So adjusting limit screws you may run into a cable tension problem, or b-tension problems, or discover that your housing needs replacing. Don’t be intimidated, just take your time.
Limit screws are used to, you guessed it, limit the rear derailleur. Since the spacing on frames and cassettes vary slightly, and some bikes are 7, 8, 9, or 10 (ok Campy or 11) speeds there needs to be a way to set limits for the amount the derailleur can travel. By adding limit screws it means a lot of the time you can use the same derailleur for 7, 8, 9, or 10 speeds.
Limit screws are little screws that physically stop the rear derailleur from moving out of a certain range regardless of what your shifter is doing. They are like the bookends and have no function unless you are in your easiest or hardest gear on the back.

Here you can see the limit screws on the sexy Ben-meya derailleur and how they contact the body of the derailleur to limit its movement.
This is the other limit screw on the Ben-meya. One for the High limit, one for the Low limit.

Tools needed:
-Slotted screwdriver
-hand

It is important to select a screwdriver that fits snugly into the limit screw. Some limit screws are soft aluminum (like the ones on my 7900 DuraAce) so by selecting a tool with a secure fit it will ensure that you don’t damage the head of the screw (which sucks as you might have guessed). Also note that some derailleurs you need Allen keys to adjust the limit screws (SRAM XO and others) and they may be located in an entirely different place on the derailleur. Just look for the two screws labelled “L” and “H”. Sometimes you can also tell which limit screws they are by shifting to either the lowest or highest gear and locating the screw that is blocking the derailleur from moving beyond that point (as pictured above on the Ben-meya).

As always, make sure your wheel is square in your frame. I do this by leaning over the bike from the other side, putting my weight down on the saddle to keep the wheel square in the dropouts, and closing the skewer while my weight is keeping the wheel square.

Tighten

Step 1:
Shift your rear derailleur into the hardest/smallest cog on the back. Locate the limit screws on your rear derailleur. On my DuraAce they are at the back and labelled “L” for Low (easiest) and “H” for High (hardest).


Step 2:
Check your High limit.
When you are in your hardest gear the upper pulley wheel on the derailleur should sit squarely in the centre of the hardest cog when viewed from the back. Spin your cranks so that your chain is moving to make sure it is running smoothly along the hardest gear if it does look centred.

Symptoms of improperly adjusted High limit:
Screwed in too far
-chain wants to jump up to the next easiest gear. In doing this your chain makes a *clicking* noise every time your cassette makes a revolution or your chain hunts around between the two hardest gears (or doesn't go into the hardest gear at all).
Screwed out too far
-chain wants to jump off the hardest cog and into the frame. It can get jammed in there and wreck your chain, derailleur, frame, hanger, ect……


Step 3:
Adjust your High limit.
Use your snug fitting screwdriver to make the appropriate adjustments. If you are screwing out counter clockwise and your derailleur isn't moving down towards the hardest cog it means the derailleur is being held in place by cable tension. Release some cable tension with either the barrel adjuster on the shifter/derailleur, or by loosening the cable pinch bolt on the rear derailleur. This will allow the derailleur to rest on the High limit screw.
*You rear derailleur will always rest on your High limit screw when you are in your hardest gear if your High limit is adjusted properly.
When cable tension and High limit screw are in harmony there is often just a tiny bit of slack in the cable when in your hardest gear on the back.

Here you can see there is lots of slack in the cable which will allow me to adjust the High limit as I please.



When it's all said and done there should be the smallest touch of slack in the rear derailleur cable and the derailleur should rest against the High limit screw when in the hardest gear.

Step 4:
Final check of your High limit.
You want to stress your High limit to make sure that your chain is not going to jump off the cog and into your frame. To stress your High limit and expose it to the kind of forces it will encounter out on the trail you need to and pull your rear derailleur to try and get the chain to come off into the frame.
Do this by firmly grasping the derailleur in your hand. While spinning the cranks, pull outward with a small amount of pressure. If the chain jumps off into your frame it means you need to tighten the High limit screw a bit more by turning it clockwise.
Finish up with your High limit.

Chain will fall off when derailleur is loaded by hand if not properly adjusted.
Step 5:
Check your Low limit
When you are in your easiest gear your upper pulley wheel on your derailleur should sit squarely in the centre of your easiest cog on the back. Again spin your cranks to make sure your chain is moving smoothly along this gear.

Symptoms of an improperly adjusted Low limit:
Screwed in too far
-chain wants to jump down to the next hardest gear. Makes a *clicking* noise with every revolution of the cassette or the chain hunts around between the two easiest gears or doesn't shift into the easiest gear at all.
Screwed out too far
-chain wants to jump off the easiest cassette and get lodged in your spokes. This is the most common cause of death for a rear derailleur/chain. Often the derailleur cage will get caught in your spokes and the whole derailleur will get ripped right off the bike. Usually it making a big mess of your rear wheel in the process.


Step 6:
Adjust your Low limit.
Again use your screwdriver to make the appropriate adjustments. Essentially just screw in your Low limit clockwise until it snugs against your derailleur when you are in your easiest gear. Or if your derailleur won’t make the shift to your easiest gear then screw your Low limit out counter clockwise to allow your rear derailleur to travel a little bit further up the cassette to complete the shift.
*You rear derailleur will always rest against your Low limit screw when you are in your easiest gear if your Low limit is adjusted properly.
When cable tension and Low limit screw are in harmony you should feel your derailleur just touch your Low limit when shifting into your easiest gear. Not enough to make it hard to shift into that gear, just enough to know that it is resting against the Low limit screw.

Step 7:
Final check of your Low limit.
Now you want to stress your Low limit to make sure that your chain is not going to jump off the easiest cog and into your spokes. To stress your Low limit and expose it to regular every day riding forces you need to push on your rear derailleur to try and get the chain to come off into the spokes.
Again grasp the derailleur firmly in your hand. While spinning the cranks SLOWLY, CAREFULLY push your derailleur towards your wheel with a small amount of force. If the chain jumps off into your spokes makes sure your wheel is moving slowly enough to not damage your chain/spokes/derailleur in the process. If it does jump off it means you need to tighten your Low limit screw a bit more by turning it clockwise.
Finish up with your Low limit.

Chain will fall off into spokes when pressured by hand if the Lower limit is not properly adjusted. Better here than being torqued up a hill out on the trail!
That’s if my friend you are all finished! Again, takes some fiddling back and forth but eventually you will get it. After a while you will get a feel for it and you will be able to troubleshoot almost any problem that comes your way concerning shifting. Every bike is different and practice makes perfect.


Let me know if you have any questions, concerns, comments, stories.

Benno

4 comments:

  1. thanks man! this just what I've been looking for for the last three months
    this kicks so much ass.really nice tuto, i'm sure my bike will be happy I found this
    Special thanks from El Salvador!
    Gracias amigo!!

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  2. This comment has been removed by the author.

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  3. Hey Miguel,
    Sorry I am so late to reply, just browsing my old postings making sure they are up to date still. Glad I was able to help clarify things for you regarding limit screws. Other riders always seem amazed when I make micro limit screw adjustments like I'm some sort of wizard lol. Little do they know just how easy it is!

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  4. What do you do if one of the limit screws is missing? Running fine at the mo' but when the back tyre needs changing...

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