Derailleur Maintenance and Tuning

2007.11.11

Mike Daniels

Key points:

To get the best performance (e.g. smooth, quick, and quiet changes) and long life from a Derailleur transmission it must be kept:

CLEAN, WELL LUBRICATED, AND CORRECTLY ADJUSTED.

Since the system is mechanically vulnerable, the degree of maintenance required varies considerably with the weather and road conditions which you ride in, and how carefully you protect the components from physical damage.

Keep the cassette sprockets, jockey pulleys, and chain ring sprockets free from built up greasy debris.
Lubricate the chain frequently and keep it clean. The interval depends very much on weather, road conditions, and distance ridden,.
Suggest re-lubing every 500-1000Kms

Cleaning every 1000-2000Kms (e.g.at least twice in the cycling season).
Lubricate the front and rear derailleur pivot points and cables occasionally
Suggest twice in the cycling, season, a minimum of once per year.
Check that there is no damage to the rear derailleur cage or support arm, e.g. they sometimes get bent after a fall or when transporting the bike
To get the best life and reliability worn parts should be replaced as soon as detected.
Specifically:
Check the chain for wear after cleaning (measure chain length). Note:
Continuing to use worn chains is false economy, they will shorten the life of sprockets and chain rings
New chains are cheaper than sprockets!
Check the cables to the front and rear derailleurs ensure there are no broken or frayed strands along their length
(Broken cable strands can get caught in the outer cable and prevent the derailleur from functioning smoothly).

Adjusting the Rear Derailleur for correct operation:

There are 3 possible adjustments
1. LIMIT STOPS: These small screws control the amount of movement of the derailleur cage, usually labeled 'H' & 'L'
  
  If the stops are incorrectly adjusted the derailleur cage may:
  "Over travel" allowing the chain to jump off the cassette's high or low cogs.
  
  Or "undertravel" so that you can't select the highest or lowest cogs
  
  Normally these adjustments don't change so if it's necessary to re set them it may be due to damage to the derailleur, e.g a bent cage
2. CABLE TENSION: This 'barrel screw' adjustment controls the position of the cage for any gear selected
  
  It's the most often needed adjustment to ensure smooth changing and noise-free operation. Usually necessary due to general wear and tear and/or cable stretch, but can also be required due to damage to the derailleur, e.g. a bent cage.
3. "B" SCREW: You normally don't need to touch this unless you have changed parts such as a new cassette
Adjusting the Front Derailleur for correct operation:

There are 2 possible adjustments
1. LIMIT STOPS: these small screws control the amount of movement of the derailleur cage
  If the stops are incorrectly adjusted the cage may:
  "Over travel" allowing the chain to jump off the high or low chainring.
  
  Or "undertravel" so that you can't select the highest or lowest chainrings
  
  Normally these adjustments don't change so if it's necessary to readjust it may be due to damage to the changer, e.g a bent cage, or movement of the changer assembly on the frame downtube
2. CABLE TENSION: this adjustment controls the position of the cage for any selected chainring.
  Note: Often there is not an adjuster for this purpose so the cable clamp will have to be slackened to make small cable length changes
  This is the most often needed adjustment to ensure smooth changing and noise-free operation.
  Usually due to general wear and tear and/or cable stretch, but can also be necessary to readjust due to damage to the derailleur, e.g a bent cage or movement of the changer assembly on the frame downtube.

USEFUL Links if you need more information:

An excellent article by Sheldon Brown:
http://www.sheldonbrown.com/derailer-adjustment.html

Others:
http://www.cobr.co.uk/e-cobr_information/workshop/introduction.shtml
http://www.parktool.com/repair/readhowto.asp?id=641