How to Reattach the Gear Mechanism on a Mountain Bike

a downhill mountainbike gear wheel and gearshift mechanism image by Stephen Gibson from Fotolia.com

A bicycle gear mechanism, or "mech" for short, is technically known as a derailleur. These mechanisms can be removed, cleaned, and oiled. Due to off-road activity, mountain bike gear mechanisms are particularly prone to grit and grime. Removing the mechanism from the bicycle may be the only way to adequately clean it. Reattaching it will take a little more time. But, if the entire process is done correctly, your mountain bike will be shifting cleanly and efficiently once again.

Instructions

Difficulty: Moderately Easy

Things You’ll Need:

5 mm and 3 mm Allen wrenches
Needle-nose pliers

Step 1

Use a 3 mm Allen wrench to unscrew the bolt at the center of the lower mechanism pulley. This pulley is held between two plates called the derailleur cage. Set the pulley and its bolt aside for the moment.

Step 2

Attach the mechanism pivot bolt, on the backside of the mechanism body, to the mechanism hanger on the bike frame. Use a 5 mm Allen wrench to tighten the bolt.

Step 3

Move the chain by hand to the smallest rear sprocket (if it is not already there). This will put the chain in position to be threaded through the mechanism pulleys.

Step 4

Pass the chain around the front and then beneath the upper mechanism pulley. You may need to spread the cage plates in order to fit the chain beneath this pulley.

Step 5

Press the lower pulley (the one you removed) against the inside of the chain, and push the pulley, and chain, back to its former place inside the derailleur cage.

Step 6

Hold this pulley in place and insert its fixing bolt back through center of the pulley. Tighten the bolt with the 3 mm Allen wrench.

Step 7

Shift your rear gears so that the shift cable has the greatest amount of slack. This would be the equivalent of shifting the chain to the outermost, or smallest, rear sprocket.

Step 8

Pass the shift cable through the cable opening at the back of the mechanism.

Step 9

Pull the end of the cable taught with a pair of needle-nose pliers, and tighten the anchor bolt on the bottom of the mechanism over the cable. The bolt requires a 5 mm Allen wrench.

Resources

ParkTool: Rear Derailleur Adjustments

Article Written By Matthew Ferguson

Matthew Ferguson is a writer living in Savannah, Ga. He has been writing for over 10 years and his work has appeared on various online publications. A collection of his short stories was published in spring 2010. He is a graduate of Appalachian State University.

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