Your Front Derailleur

How to Adjust It
by Geoff Slater

Nothing can make an MTBer feel more helpless than not being able to service their own bike.

One area that needs TLC more often than not, is the bike's transmission. What's that noise? What are all those cables and adjustment screws for? How do they all work? Where do I start? Your MTB guide is here to help.

The first part of a bike's transmission that tends to get a little screwy is the front derailleur, so this my friends is where we'll begin...

The Front Derailleur
Most front derailleurs on mountain bikes today are of the Shimano Deore type (meaning Deore, LX, XT, XTR). What follows is an in-depth look at how you, a budding MTB technician, can squeeze some performance out of this sometimes-troublesome piece of Japanese hardware.

Just Do It
To begin with, elevate your rear wheel in some creative manner. Either suspend your bike from the ceiling or clamp it in a work stand; what you're looking for here is to have the drive train and rear wheel free to spin.

Removing The Front Derailleur

• Shift the chain to the smallest chain ring and the largest cog.
• Loosen the cable attachment bolt and remove the cable from the derailleur.
• Unclamp the unit from the seat tube.
• On the bottom end of the derailleur cage assembly is a bolt that keeps the cage closed. Remove this bolt and carefully pry it apart, slipping the chain out of the cage. (Do not pry too hard and bend the cage.) Now the derailleur is removed. Look it over. Notice the two adjustment screws and see what they do. Play with it. Get to know it. The "L" on one of the adjustment screws stands for low-gear (small chain ring), and the "H" on the other stands for high-gear (large chain ring). Adjusting them while the derailleur is off the bike will allow you to see that these screws act as nothing more than "stops", and allow positions to be fixed in any position you think is appropriate. These are the positions that you must locate. For the time being, however, just loosen them so they are making no stops at all. (Simply turn them both most of the way out.)

The Barrel Adjuster
On the left hand shifter - where the cable runs into the shifting mechanism - is an adjusting screw called the barrel adjuster. It is there to remove any slack in the cable after the adjustment of the derailleur is complete. More on that later. What is important now is that the barrel adjuster is turned out to its "slackest" position. Holding the free end of the derailleur cable and turning the barrel adjuster can check this. If it is pulling the cable towards the shifter your turning it the wrong way. Draw as much cable towards the derailleur as the barrel adjuster will allow.

Front Derailleur Installation
Now you're ready to put the derailleur back on the bike.

• First, move the chain out of the way. Slip it off the smallest chain ring, allowing it to sit on the bottom bracket of the bike. (It is much easier to position the derailleur without the chain in the way).
• Next, position the derailleur so that the height of the cage passes 1/16" to 1/8" above the highest point of the outer chain ring.  Moving the derailleur through its shifting motion with your thumb can check this. Also, the outer plate of the derailleur cage should run parallel to the chain rings when viewed from above.
• With the low-gear adjustment (marked "L" for low), position the derailleur cage in the center of the small chain ring when viewed from above.
• Re-attach the cable to the derailleur and take up the slack with the barrel adjuster. The cable is at the proper tension when the derailleur moves as soon as the shifter does.
• The chain can now go back in place. Carefully pry the cage open and slip the chain back on the smallest chain ring.
• Replace the screw that closes the bottom of the derailleur cage.

Limit Screw Adjustment Low-gear
Shift rear derailleur to the largest cog. When shifting back and forth between the small and middle chain rings, and the chain drops off the small chain ring to the inside, tighten the low-gear screw 1/2 turn and shift again. If the chain does not drop off easily from the middle to the small chain ring when shifted, loosen the low-gear screw 1/2 turn and shift again. Find the happy spot.

Limit Screw Adjustment High-gear
Shift rear derailleur to the smallest cog. When shifting back and forth between the middle and large chain rings, and the chain jumps over the large chain ring, tighten the high-gear screw 1/2 turn and shift again. If the chain is slow to go from the middle chain ring to the large one, loosen the high gear screw 1/2 turn and shift again. Find the happy spot.

Fine Tuning
Once you have set the derailleur adjustments to your liking, you may want to fine-tune the barrel adjuster to eliminate any noise from the chain rubbing the derailleur in some cross gears, or just to make the shifting a little more precise. On a 27-speed drive train you should not be running cross gears too often. (e.g.: large front chain ring large rear cog; small front chain ring small rear cog.) This will result in rubbing on the front derailleur and stress on the chain. Too much rubbing can be from misusing gear combinations. Instead, shift often and run your chain straight.

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