A bottom bracket is the primary component in the pedal system of your bicycle. The bracket resides in a circular hub where the lower tubes of your bicycle frame intersect. A chain-ring assembly attaches at one side of the bracket and pedal cranks attach at each end of the bracket spindle. The tools needed to access a bottom bracket vary with the particular type of bracket.
Cartridge
The first order of business when accessing the modern cartridge bottom bracket is removing the pedal cranks. Small, plastic caps cover hex-head bolts that secure each crank arm to spindles on each end of the bracket. You pop the caps off with a small screwdriver to access the bolts. A crank tool is used to loosen and remove each crank bolt as you hold that crank arm steady with one hand. Your crank puller removes the cranks from each spindle with a prying motion. With the right and left bracket nuts now exposed, you install a lock ring tool on the inside ring of a nut and turn the tool with a bottom bracket wrench. The cartridge threads out of the hub by hand once the lock ring nuts are removed.
Cup and Cone
Similar to a cartridge type, accessing a cup and cone bracket begins with removing the pedal cranks using a crank tool and crank puller. Once the cranks are removed, you install a pin wrench behind the adjustable bearing cap on one side of the bottom bracket. Inserting both pins of the wrench into slots on the bearing cap allows you to apply opposite force while loosening the lock ring. Unlike the cartridge lockring, the cup and cone lockring has splines on the outer edge, allowing you to loosen the ring with a lockring wrench. Bearing cups on each side of the bracket are removed with your small screwdriver. Bearings on each side are removed by pushing the bottom bracket side-to-side in the hub. The spindle, or axle in this case, is removed by hand.
One-Piece
Most likely, your vintage bicycle has a one-piece bottom bracket that you identify by large nuts and flat bearing caps at each side of the hub. The unit is aptly named for the one-piece unit that consists of the axle and both pedal cranks. In this regard, the one-piece is not a typical bottom bracket, but a crank unit. Once the pedals are removed from each crank arm, your adjustable wrench is used to remove the left side nut. A keyed washer is removed by hand and a lock nut behind the washer is removed with your wrench. The left bearing cone is removed with your screwdriver and the retainer ball behind the cone pulled out by hand. The one-piece crank unit is then maneuvered through the hub and removed.
Bottom Bracket Adjustment
Opposite threads on each end of the bottom bracket prevent the nuts from loosening as you pedal. During installation, the nuts are tightened to a point where the bracket is stable in the hub. Pedaling your bicycle self-tightens the nuts to the appropriate tension. Most bicycle experts concur that modern bottom brackets need no adjustment other than pedaling the bike following installation of the bottom bracket. One-piece brackets require the nuts to be tightened securely with your adjustable wrench.
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