Cutting Cable Housing
This article will discuss the cutting and sizing of both brake and derailleur housing. See also related article Brake and Shift levers.
Typical Tools and Supplies:
- Cable Cutter: CN-10
- Brake housing and cables as needed
- Shift housing (compressionless) and cables as needed
- Housing end caps (ferrules) as needed
- Light lubricant
- Mill file (for brake housing as needed). Bench grinder or dermel also useable.
- Hex wrenches for cable binder bolts
The Park Tool CN-10 is designed to cut multi-strand wires such as gear and brake cable, brake housing, and compressionless gear housing. Compressionless shift housing uses many inner support wires running longitudinally with the inner plastic liner. Compressionless shift housing is intended for shifting systems only, not braking. Brake housing is made of a wire wound around a plastic liner. Use ends caps or ferules at the ends of housing when ever possible. It is recommended to lubricate inside the housing or the cable is installed.
The jaws of the cable cutter surround and then sheer the material. Using plain diagonal cutters can simply flatten and smash cables. As with all cutting tools, it is recommended to wear eye protection.
Grab and hold the cable or housing close to the jaws. Use care not to cut your fingers. Hold cable or housing perpendicular to jaws and squeeze levers quickly for a clean cut, as seen below.
After cutting the compressionless gear housing, inspect the end to see if it flattened a bit. Use the crimper section of the CN-10 or CN-4 to open up the housing and inner liner before installing an end cap and cable. You can also use the crimper section cutter to crimp on a cable end cap, as seen below.
How Long Should Housing Be?
Brake and gear housing allows the cable wire to be routed around bends and connects the levers to the frame stops. The less the drag on the cables, the better for the shifting and braking. Too short of housing will cause it to kink and bind, making even more friction. As a rule of thumb, try to size the housing so it is as short as possible but it still enters the stops and barrel adjusters in a straight approach. For the rear derailleur housing, note especially how the housing enters the barrel adjuster.
In the image above, the housing bends immediately upon leaving the barrel adjuster. This can actually bend the housing end cap. The image to the right shows how longer housing in this case allows the housing to enter straight.
The image above is a typical new bike housing length. The housing bends and kinks as it enters the barrel adjuster. The image to the right shows longer housing allowing a straight entry into the barrel adjuster.
The image above shows brake and shift housing which is much too long. The housing could be shortened and still have a smooth, straight approach to the levers and housing stops.
The routing of housing may affect the length. Typically the front derailleur shift housing is run on the left side of the frame, while the rear derailleur shift housing is run on the right. This may at time cause unnecessary bending in the housing. In some cases, it is possible to "cross over" the housing, running the front shifter to the right side stop, and the rear shifter to the left side stop. It will then be necessary to again cross the cable. Consider this option, but if the cable ends up rubbing the frame, it is not a good idea. There may be some light rubbing between cables, but this would result in less friction than poorly routed housing.
Shift lever housing that is too long. Housing passes center line of bike, then must bend back to housing stops.
Shift housing is crossed over at headtube, and crossed again on downtube. Arc of housing is much smoother than black housing in example of too long housing.
Cutting Brake Housing
Brake housing is typically made of single strand flat wire wrapped around an inner plastic tube. This housing may be cut with the CN-10, CN-4, or diagonal pliers. Because of the design of the housing wire, it is not always possible to get a flat, clean cut. It is best to finish any burr with a file. Lightly grinding the end will also improve the housing and reduce friction. NOTE: Compressionless housing does not require finishing.
Adjustment of the CN-4
As a cable cutter wears, it may require readjustment for best cutting results. Grab the handles and wiggle them against the axis of the thread. If there is play between handles, turn locknut counterclockwise to loosen nut, turn bolt head clockwise slightly to tighten adjustment, and retighten locknut. Repeat adjustments as needed until tool cuts cable cleanly. If handles bind, turn locknut counterclockwise to loosen nut, turn bolt head counterclockwise slightly to tighten adjustment, then retighten locking nut. Repeat adjustments as needed until tool cuts cable cleanly.