How to Fix a Bottom Bracket on a Mountain Bike

How to Fix a Bottom Bracket on a Mountain Bike
Modern higher-quality mountain bikes use a "cartridge style" bottom bracket. While this style of bottom bracket is more durable and longer lasting, it is also non-serviceable, meaning that it must be replaced when it breaks or wears out. Replacing a bottom bracket requires specialized tools that are available from any bike shop.
 

Instructions

Difficulty: Moderately Challenging

Remove the Cranks

Things You’ll Need:
  • Socket wrench with metric sockets Adjustable (crescent) wrench Crack extractor Bottom bracket tool Grease Rags
  • Socket wrench with metric sockets
  • Adjustable (crescent) wrench
  • Crack extractor
  • Bottom bracket tool
  • Grease
  • Rags
 
Step 1
Shift the bike into the smallest front chain ring, then derail the chain so that it is resting loosely against the bottom bracket shell. There is no need to remove the chain completely. Remove the dust caps from the cranks. The dust caps are small plastic or metal caps which cover the bolts attaching the cranks to the bottom bracket.
Step 2
Using the socket wrench, remove the bolts that attach the cranks to the bottom bracket. Most bottom bracket bolts use a 14-mm socket.
Step 3
Ready the crank extractor by backing out the inner threaded section as far as it will go without removing it completely. Apply a small amount of grease to the threads of the outer section of the crank extractor.
Step 4
Thread the outer section of the crank extractor into the threads of one of the cranks. Tighten the extractor with an adjustable wrench, while holding onto the crank to stop it from spinning.
Step 5
Tighten the inner section of the crank extractor until the crank pops off the bottom bracket. Repeat Steps 3 through 5 for the other crank.

Replace the Bottom Bracket

Step 1
Use the bottom bracket tool and the adjustable wrench to remove the bottom bracket and bottom bracket sleeve. The non-drive side of the bottom bracket shell is reverse-threaded, meaning that it needs to be turned clockwise to remove it. The drive side is standard-threaded.
Step 2
Clean out the bottom bracket shell using a cloth. Remove as much dirt and grease as possible.
Step 3
Grease the threads of the new bottom bracket and of the bottom bracket sleeve.
Step 4
Thread the bottom bracket into the bottom bracket shell, from the drive side. Using the bottom bracket tool and adjustable wrench, tighten the bottom bracket until its outer lip is flush against the rim of the bottom bracket shell.
Step 5
Install the bottom bracket sleeve into the other side of the bottom bracket shell. It may not tighten down until flush; this is normal. Remember, the non-drive side is reverse-threaded.

Reassembly

Step 1
Install the cranks onto the bottom bracket and tighten down the bottom bracket bolts using the socket wrench.
Step 2
Reinstall the dust caps.
Step 3
Reposition the chain and you are ready to ride your bike.
 

Tips & Warnings

 
Always test ride your bike after doing any repair. Conduct your test ride in a safe spot away from all other traffic.

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