Shimming the Vespa transmission made easy
In order to be able to adjust the sprocket free play on the main shaft you will need the corresponding transmission shims and two thickness gauges (you really need them twice) for measuring the transmission.
It is best if you begin in first gear with a standard shoulder ring measuring 1.0mm so that later on when everything is mounted the gears firmly stay in place and you can properly shift the transmission into the neutral gear.
Beginning below the first gear using a shoulder ring that is too thick could cause the gear selector cruciform to no longer be in a free position between the sprocket segments and make it want to engage the sprockets in the neutral.
Checking the transmission free play
You can now check the sprockets‘ free play using the thickness gauges.
After mounting the parts the free play should range from 0.05mm to 0.15mm. In transmissions that entirely consist of new components you should rather opt for a tighter free play because the components have yet to “adapt to one another”.
Do not choose too little free play
What you should not do either is overdoing it and allowing too little free play. This will result in the contrary of what you want on a running transmission. The hardened surfaces of the sprockets and shoulder rings tend to chew in, hence drastically increasing the free play within a short period.
If you want to replace individual sprockets of your transmission, we recommend that you order a set of shoulder rings ranging from 1.0mm to 1.3mm right away. And while you’re at it anyways, have a look at the gear selector cruciform. Do not try to save on transmission oil and replace it – and don’t forget to use new O-rings.
The right tools in good quality for your scooter will always help you do the job.