Gear-shift cables in a vintage Vespa scooter provide the critical control for the user to change gears as the scooter is operating. Changing the cable, however, does not pose a large problem when following the necessary steps.
Provide for a clear workspace if the repair is being performed in a garage. Pull over to a clear area off a road if the repair occurs while en route to a location. Unpack all your tools so they can be easily accessed. Unpack a hand towel or paper towels to clean excess grease off as needed.
Remove the headlight, the speedometer or the scooter headset top with a screwdriver to gain access to the gear lever cable control inside; the part removed will depend on the model scooter owned. Disconnect the gear lever box cover at the bottom of the scooter underneath the main engine body. Determine which gear lever cable is broken; there are two controlled by the gear lever handle.
Pull the top end of the cable out of the gear lever control. Pull the bottom end of the broken cable out of the gear lever box. Remove the cable securing nut off the bottom end of the broken cable. Do not throw it away. Take the remaining cable remnants and dispose of them. Clean off any excess dirt or grease from the cable housing ends that the cable remnants came out of.
Unpack your replacement cables and unroll the new cable to be used so it is fully extended. Place it somewhere off the floor or ground to avoid contamination. Take a dab of grease, hold one end of the cable with the securing tab on the end, and run the grease with your hand down the cable. Make sure the entire cable is greased.
Take the non-tabbed end of the greased cable and insert it into the cable housing in the headset. Slowly feed more of the cable into the housing, twisting as needed to get it go through to the end at the bottom of the scooter. Look for the end to poke out by the gear lever box underneath the engine. Insert the securing tab on the other end of the gear lever cable into the gear lever control attached to the gear lever handle. Then, take the end poking out of the gear lever box and pull all remain slack through the cable housing so the top is snug in the gear lever control.
Confirm the gear lever handle is in the same position as the gearing of the engine--i.e., neutral. Slip on the gear securing nut to the cable end sticking out of the gear lever box. Do not secure it yet. Place the nut with the cable running through it into the slot where the nut sits, similar to the other gear lever cable nut next to it. Use the cable-securing tool to secure the cable before tightening, removing any remaining slack in the cable. Pull on the cable tightly if no securing tool is available. Use the 7mm crescent wrench to tighten down the top of the securing nut onto cable to secure it. Use the 7mm and 8mm wrenches to finish tightening but avoid doing so much that the cable is cut. Snip off the remaining end of the cable past the securing nut once tightening is complete.
Add a bit of grease around the gear lever box internals and then replace the box cover. Replace whatever was removed from the headset to gain access to the gear lever control. Clean up remaining trash and put away your tools.
Vespa scooter control cables snap frequently due to corrosion, age and wear and tear. Cables for the clutch and gear lever controls should be replaced annually, since these cables take the most abuse when riding.
Do not overtighten control cables. This will cause then to break and snap under use. It will also make it very hard to shift gears.