Typically, a clicking sound when you pedal uphill on your mountain bike indicates that something needs adjustment. The chain and derailleurs must be properly adjusted to reposition the chain correctly when you shift gears. An improperly adjusted shift cable can reduce the efficiency of a derailleur, causing the chain to travel against the side of a sprocket. In most cases, you can resolve clicking by adjusting or lubricating a particular component on your mountain bike.
Chain
The chain on your mountain bike relaxes when you coast and tightens when you pedal. A loose chain might click or pop when you exert more power to pedal uphill. Before you adjust the chain, inspect it closely for signs of excessive wear, such as worn or broken roller links. If the chain is not worn or damaged, refer to your service manual and adjust the chain to the proper tension. If the clicking persists, the problem might be a derailleur.
Derailleurs
A derailleur can be adjusted to allow you to correctly position the unit in relation to the sprockets. If you hear clicks when shifting gears on an incline, the front or rear derailleur is not positioned correctly. Identify which set of sprockets is clicking and adjust the appropriate derailleur. The front derailleur has a positioning clamp on the bike frame that you loosen to adjust the unit so the cage doesn't ride atop the chain. Use a 2 mm feeler gauge to set the correct clearance between the bottom of the cage and the upper surface of the chain and tighten the clamp. The rear derailleur has an adjustment screw that you turn with a screwdriver. Turn the screw in or out until the lower swing-arm is exactly vertical, or parallel with the rear cassette sprocket. If you still experience clicking and the chain and derailleurs are properly adjusted, check the shift cables.
Cables and Shifters
Looking at the front and rear derailleur, you notice a barrel adjuster where the shift cable attaches top of the front derailleur and at the back of the rear derailleur. Take a test ride and use the appropriate shift lever to shift each derailleur and determine the nature of the adjustment. If a derailleur is slow to respond, turn the barrel adjuster clockwise a full turn by hand and repeat the test. If a shifter is hard to operate, loosen the barrel adjuster on the corresponding derailleur a full turn and test it again. You make minor adjustments using the barrel adjusters at the shifters as you ride.
Lubrication
Lack of lubrication can cause the chain to click because of metal-on-metal contact with the sprockets. In addition, dry contacts between the rear dropout surfaces and the axle or quick-release surfaces can cause clicking at the rear wheel when you pedal uphill. Your service manual has lubrication procedures and lists the recommended lubricant for particular components. Many experts suggest using an all-weather chain lube that holds up in wet conditions. Typically, axles and dropouts are lubricated with lithium grease. When all components are adjusted and lubricated and clicking persists, consult an experienced mountain bike mechanic and describe the steps you've taken. This could avoid compounding another type of problem that might result in a costly repair.
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