The Vespa "old PX" drive shaft, also built in Sprint, Rally and other models, has a collar on the tire side, which means there's no recess for the cruciform to grip for power transmission. Slipping gears is often a problem if your selector box is in poor shape or has seen better days allowing the cruciform to slip and slide.

PX Lusso drive shafts built from '83 on up have 2 security rings and 2 shoulder rings instead of a collar. There are small recesses in the slide groove of the cruciform: the cruciform locks into gear at power transmission making this the no. 1 choice for tuned motors. If you're looking for a new transmission for a tuned motor, the Lusso transmission is the one.

SIP-TIP: Absolutely important to use the right selector box, shift rod, cruciform and gear wheel. Best source to order from is from our online replacement part catalog. Gear up with SIP!