When to Replace Cables
Replace cables and housing together — fitting a new cable into old housing negates most of the benefit. Signs it's time:
- Shift cable: gear indexing drifts frequently, barrel adjuster is near the end of its travel, cable is frayed or kinked, or it's been 2+ years since the last replacement.
- Brake cable: lever feels vague or the lever pulls too far before braking, visible rust or fraying near the anchor bolt or inside the housing, or housing feels rough when you compress it by hand.
- Housing: cracks in the outer sheath, hard spots (indicate internal corrosion or damage), or if new cables are being installed — always replace together.
Tools and Materials
Step 1 — Measure and Cut the Housing
Before removing anything, note how long each housing segment is. The easiest method is to cut new housing to exactly the same length as the old pieces. If you're changing the routing or have no reference, a good rule is: the housing should allow full handlebar turn in both directions without pulling taut or creating kinks, and should follow the most direct clean path between cable stops.
Use proper bike cable cutters — they cut in a shearing action that leaves a clean, flat end. Side-cutters crimp the housing closed. After cutting, the inner liner of the housing is often collapsed. Use an awl, a sharp nail, or the tip of a spoke to push the liner open so it's circular again. A collapsed end pinches the inner cable and causes sticky, imprecise shifting or braking. Fit a ferrule over each end before installing.
Step 2 — Route the Cable
Thread the new inner cable through the lever or shifter first. On Shimano STI levers, shift to the highest gear (smallest sprocket) to expose the cable entry port — it's usually visible with a flashlight. On MTB trigger shifters, the port is usually on the inboard face. The cable nipple must seat fully in the lever pocket — a partially seated nipple will pull through under load and leave you with no gears.
Thread the inner cable through each housing segment and cable stop in sequence. Apply a thin smear of cable lubricant to the inner cable as you thread it through each housing piece — do this before fitting ferrules and cutting to final length. The inner cable should slide freely through the housing with light finger pressure. Any stiffness suggests a collapsed housing end or sharp bend in the housing routing.
Pull the inner cable taut and clamp it at the derailleur or caliper anchor bolt. For shift cables, the correct tension starting point is: pull the cable taut by hand (not yanked) and tighten the pinch bolt to the specified torque (usually 5–6 Nm for Shimano). You'll fine-tune with the barrel adjuster after routing.
Step 3 — Set Initial Tension
For rim brakes, anchor the cable with the pads sitting about 1–2mm from the rim surface. Squeeze the lever — it should feel firm at roughly two-thirds of the travel distance to the handlebar. Too far from the bar means cable is too slack (loosen the anchor bolt, pull more cable through, re-clamp). Too close to the bar means over-tensioned. For rim brakes, the straddle cable or yoke height (on cantilever/V-brakes) affects the mechanical advantage — refer to your brake manufacturer's setup specs.
After anchoring the shift cable with medium hand tension, follow the indexing procedure in the Derailleur Adjustment guide. New cables will need the barrel adjuster wound out (counter-clockwise) about 2–3 turns more than you'd normally need — they'll stretch in over the first few rides and require re-adjustment.
Cable Stretch — The First Few Rides
Before finalising tension, pre-stretch the cables. For brake cables: clamp the lever hard several times. For shift cables: back-pedal while pulling the cable taut with your hand (or shift through the full range several times). This removes the initial slack from the cable seating into the housing ends and lever/caliper anchor grooves. Re-tension after pre-stretching and you'll need far fewer mid-ride barrel adjuster corrections.
Leave 2–3cm of cable protruding beyond the pinch bolt — enough to re-tension if needed, not so much it catches on things. Crimp a cable end cap onto the end using the flat side of cable cutters or pliers. An uncapped cable frays within a few rides and becomes impossible to thread back through the housing.
Tips and Common Mistakes
- Don't over-tension brake cables. Pulling the cable too tight before clamping means your barrel adjusters are maxed out from day one with no room to compensate for stretch. Start with moderate tension and use the barrel adjuster to fine-tune.
- Wrong housing length is the #1 mistake. Too short and the cable pulls taut on full handlebar turn, steering and braking simultaneously. Too long and the housing sags and kinks, increasing friction. Check full lock both ways after routing.
- Lube the inner cable, not the housing outside. Lubricant on the outside of housing makes no difference and attracts dirt. Lube the inner cable as it's being threaded through.
- Full outer housing to the rear derailleur. Many bikes have a full outer housing run from the frame to the rear derailleur rather than using the bare cable run. Full housing has higher friction but is more protected from mud and damage — a worthwhile trade for MTB.
- Electronic shifting. This guide covers mechanical (cable-actuated) systems only. Shimano Di2, SRAM AXS, and Campagnolo EPS are electronically actuated and require completely different maintenance procedures.