Bike Repair – Fit New Cables and Index Your Gears

Fitted cable on a bike frame.

If your shifting’s stiff or unreliable, follow this guide to get your gears running smoothly again.

Set things up

Make sure your bike is clean, then clamp it in a work stand. Check that the rear mech and its hanger are straight, and that the bolt holding the mech onto the hanger is tight. While turning the cranks, shift into the smallest cassette sprocket and smallest chainring. Use a 5mm Allen key to loosen the cable clamp bolts on both mechs a few turns, turning it anticlockwise.

Expose inner cables

Wind the barrel adjusters on the shifters fully clockwise, then back them off two turns to allow adjustment later. Cut the cable end caps off the old gear cables using a good quality set of cable cutters. Grip the outer gear cable next to the first shifter with your fingers and pull it out a few inches, exposing the inner cable. Repeat on the other shifter.

Shimano shifters

If you have Shimano shifters, use a Phillips screwdriver to unscrew the plastic plug on the opposite side of the shifter to the barrel adjuster, turning it anticlockwise. Put the plug somewhere safe. Push the exposed section of inner cable into the shifter. When the end pokes out the other side, pull the cable out and discard it. Repeat on the other shifter.

Newer SRAM shifters

If you have SRAM shifters with a rubber tab on top, use a 4mm Allen key or T25 Torx key to remove the shifter from the bar, turning the bolt anticlockwise. Peel the rubber tab upwards with your fingers. Push the exposed section of inner cable into the shifter. When the end pokes out from under the rubber tab, pull the cable out and discard it. Repeat on the other shifter.

Older SRAM shifters

Some older SRAM shifters have a winged screw or Allen bolt cap on top. Use your fingers/a 3mm Allen key to remove this, turning it anticlockwise. Carefully push the exposed section of inner cable into the shifter. When the end pops out from under the spring, pull the cable out – taking care not to dislodge the spring – and discard it. Repeat on the other shifter.

Changing cable outers

It may be necessary to replace the outer cables too. In this case, remove all the old outer cables from the bike. Either cut new sections to match their length or cut a single section of outer cable to the same length as the exposed part of the old inner cable to create a full-length outer cable run. Use a pick to open up the ends. Install the new outer cables on the bike.

Lube the new inner

Lightly coat the new inner cables with lubricant by running them through a cloth or sheet of workshop paper impregnated with cable lube or ‘wet’ chain lube. Carefully feed the cables into the shifters in a reversal of step 3.

Fit the new inner cable

Feed the inner cable through the narrow end of a new ferrule, then the outer cable, then the wide end of another ferrule. Push the ferrules onto the outer cable. Repeat on each section of outer cable. Pull the inner cable through until the cable head is seated inside the shifter. Refit the plug/tab/screw/cap. Refit the shifter on the bar, if removed. Repeat on the other shifter.

Adjust the rear mech 1

Turn the cranks. The chain should sit on the smallest cassette sprocket. If not, use a Phillips screwdriver to adjust the screw marked ‘H’. Turn it anticlockwise to move the rear mech closer to the frame or clockwise to move it closer to the wheel. Adjust until the rear mech’s top jockey wheel sits directly below the smallest sprocket.

Adjust the rear mech 2

Turn the cranks while pushing the rear mech towards the wheel. The chain should sit on the largest sprocket, with the top jockey wheel directly below it. If not, adjust the screw marked ‘L’. Turn it clockwise if the chain is too close to the spokes or falls off the top of the cassette. Turn it anticlockwise if the chain won’t move up from the smaller sprockets.

Adjust the front mech 1

Turn the cranks while pulling the front mech away from the frame. The chain should shift onto the largest chainring easily. If not, turn the screw marked ‘H’ anti-clockwise half a turn at a time until it does. If the chain is pushed off the chainring, wind the screw clockwise until this no longer happens. Fine tune until the largest chainring is right in the middle of the mech.

Adjust the front mech 2

Continue turning the cranks but release the front mech. The chain should drop onto the smallest chainring and stay there. If the chain falls off the chainring towards the frame, turn the ‘L’ screw clockwise. If the chain is reluctant to shift onto the smallest chainring, turn the ‘L’ screw anticlockwise. Adjust until the mech sits centrally over the smallest chainring.

Tension rear cable

Route the inner cable through the groove under the clamp bolt on the rear mech. Without moving the mech, pull the cable to apply a little tension. Tighten the clamp bolt until snug, turning it clockwise with a 5mm Allen key. Let go of the cable. Click through the gears while turning the cranks to tension the cable. Loosen the clamp bolt, take up any slack and retighten.

Tension front cable

Ensure the front mech cage is in line with the smallest chainring and the cable is correctly routed to the clamp bolt. Tension the cable and tighten the clamp bolt, turning it clockwise with a 5mm Allen key. Let go of the cable. Click through the gears while turning the cranks. With the chain back on the smallest ring, loosen the clamp bolt, take up any slack and retighten.

Index the gears 1

Turn the cranks and click through the front gears. If the chain is reluctant to shift onto the bigger rings, turn the barrel adjuster on the shifter anticlockwise. If it’s reluctant to shift onto the smaller rings, turn the adjuster clockwise. When the shifting is smooth, use your cable cutters to cut the inner cable a few centimeters from the mech and crimp an end cap in place.

Index the gears 2

Turn the cranks and click through the rear gears. If the chain is reluctant to shift onto the bigger sprockets, turn the barrel adjuster on the shifter anticlockwise. If it’s reluctant to shift onto the smaller sprockets, turn the adjuster clockwise. When the shifting is smooth, cut the inner cable a few centimetres from the mech and crimp an end cap in place.

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