Cutting and fitting gear and brake housing and cables
Level of difficulty: Straightforward
Typical tools and supplies needed
- Cable Cutter 
- Brake housing and cables as needed
- Shift housing (compressionless) and cables as needed
- Housing ferrules and cable end caps as needed
- Light lubricant
- Mill file (for brake housing as needed). Bench grinder or dremel also
- Hex wrenches for cable binder bolts
About housing and cables
With the outer plastic coating removed, the difference between
longitudinally-stranded 'compresionless' shift housing and wound
brake housing is obvious. These two varieties are purpose-specific
and not interchangeable.
Almost all gear and brake cables on bicycles are of the multi-strand
type in which many strands of wire are twisted together. 'Braided' cable,
which has the wire strands woven together as in a rope, is now rare, and
for the purposes of repair can be treated the same as twisted cable.
There are two types of housing: 'compressionless' housing, intended for
gear cables, and wound housing, for brake cables.
Compresionless housing uses many inner support wires running longitudinally
within an inner plastic liner. Compressionless housing is intended for
shifting systems only, not braking. The longitudinal strands in
this housing act to maintain constant housing length when the housing
is curved and so prevent 'ghost' shifts when the handlebars are turned.
Despite its name, compresionless housing is actually weaker in compression
than wound housing. Brake housing must resist compression when the brake
cable is pulled, so compressionless housing must not be used for brake
Brake housing is made of a wire wound around a plastic liner. This design
resists the compression that occurs in reaction to the brake cable being
pulled by the brake lever.
Housing ferrules are steel or plastic caps that fit over the end of teh
housing and have a hole for the cable to pass. Ferrules should be used
with all housings whenever possible. Cable ends should be capped with
soft aluminium cable end caps to prevent them fraying.
Cable cutters are designed to cut multi-strand wires such as gear and
brake cable, brake housing, and compressionless gear housing. 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.
After cutting compressionless gear housing, inspect the end to
see if it has been flattened a bit. Use the crimper section of the
CN-10 or CN-4 to open up the housing and inner liner before installing
a ferrule and cable. You can also use the crimper section cutter
to crimp on a cable end cap, as seen left.
Determining housing length
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 left 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 left 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 left 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.
Routing of cable and housing
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.
Left: the shift lever housing is too long. Housing passes center
line of bike, then must bend back to housing stops.
Right: 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 may be cut with cable cutters 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 cable cutters
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.
Content for this page courtesy Park Tool. For more on Park's range of
tools and workshop supplies, see: Park
Tool 's website.
 Suggested Park Tools:
- Cable Cutter:CN-10 or CN-4
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