Vespa Post 1979 Large Frame Engine Work

Transmission Rebuild

This page shows the steps to reinstall the transmission in a P series bike...which is pretty much the same as an older bike. If you'd like to replace the cush drive bearing see the page on the cush drive overhall.

Take the input cluster (sometimes called the Xmas tree) and push the axle through it with your finger so that it is flush with the bearing on the other side.

Then place it in the casing so that the helical cut gear runs underneath where the crank is located as shown. Once it is in place you'll be able to push the central axle through the small hole in the casing and the locate the cluster correctly. At this point don't push it all the way down as you'll need to add the needle bearings.

Put some grease around the area shown and slowly and carefully install the free needles so that they run all the way around the shaft.

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Above is an image of how the needles should be arranged.

Once all the needles are in, push the axle through the casing all the way until the needle area is flush with the end of the input shaft.

On the casing side you'll see where the axle pokes through....

...and there is a slot (shown with the red arrow above) that needs to be aligned as shown in the image. The alignment doesn't need to be exact as it will get finalized in the next step.

Slide on the special retaining washer so that the small tab on the inside fits in to the slot in the axle. Leave the other tabs slightly bent for now.


Then place the thick shaped washer so that the flatter side is aligned with the exterior casing shelf. It is a wise idea to roughly fit the clutch cover at this time to make sure the small recess in the cover fits over this shaped washer.

Finally, place the nut on and tighten it down, again checking that the clutch cover fits once it is tight. If it all looks good, bend the tabs up and against the side of the nut to stop it from rotating in the future.

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