Replacing Front Brake Disc Pads (PX 125, 150 & 200)
While checking front brake pad wear is one of the tasks included in the Haynes manual's Routine Maintenance Schedule for PX125, 150 & 200 electric start models (p. 121), no recommendations are given as to time intervals or distance travelled between checks. The Vespa PX Owner's Handbook (Pontedera 2001) p. 53 recommends brake pads and shoes be examined every 5,000 kms, which is perhaps a little excessive. Obviously riding styles will greatly affect the longevity of the pads, but as a general guide the pads should be inspected for wear every 10,000 kms.
As to wear, the Haynes manual states: "The pads are not marked with wear indicators but if the amount of friction material remaining is below 1.5 mm (0.06 in), new pads must be fitted."
Below are two links illustrating the procedure of replacing the pads. Take note, however, that the second link which has very clear pictures, is of a Stella, not of a Vespa, although the procedure and parts involved are almost exactly the same. The only significant difference is that the two bolts securing the caliper unit to the lower suspension arm of the Stella have regular 13 mm hexagonal nut heads while the corresponding bolts on the Vespa are round-headed sleeve bolts requiring an Allen or hex key (HX6) to remove and reinstall them.