The Vespa PX is a rugged engine, but gear selection is a weakness that gets worse with age and harder to cure with dubious quality spare parts.
There was a time when – for standard engines at least – you could usually cure gear selection problems by replacing all the usual suspects (cruciform, gear selector box, any loose gear that jumped, and re-shimming) with genuine Piaggio parts. As long as you used the right parts for the right model then your problems were over.
Sadly the quality of some spares sold as genuine parts has slipped dramatically. For the PX, gear selector boxes are a real problem. Some ‘genuine’ ones we’ve seen don’t correctly fit ANY of the Italian-made models.
There are broadly two different gearbox layouts in use in the PX; each with their own gears, layshaft, cruciform and selector rod. While the gear selector boxes for these look very similar they are actually subtly different, so it is important to match them to the correct gearbox.
PX Mk1 (pre-1984):
The early set-up uses:
- a non-flat cruciform
- a selector rod which is tightened with a 13mm spanner.
- A 2.5mm thick spacer washer between the rod and cruciform – with the counter-sink facing the rod.
It is essential that the cruciform is fitted the right way up as shown in the photo.
PX EFL & T5 (post 1984)
The later “EFL” type (also T5) uses:
- a flat cruciform
- a selector rod that is tightened with a 17mm spanner.
- No washer is used between the cruciform and rod.
The condition of the selector box is a very important item because any wear in the mechanism can make gear selection imprecise and that can lead to gear jumping and further rapid damage.
For Italian-made production there are two main types of gear selector box, and these are not interchangeable. Using the wrong type can cause gear jumping so it is vital to fit the correct one.
Know your selector wheels
Some EFL selector boxes do not have the indent mark to identify them, however it is also possible to tell the selectors apart by the shape of the 2nd gear notch (the central one of the five notches) in the wheel.
On early gear selectors the notch is a definite ‘V’-shape with two equal length sides. On EFL selectors the notch has a ‘tick’-shape with uneven length sides.
It’s still early
Early types can also be identified by the fact that with the wheel in the 3rd gear position (next-to-last position when turned anti-clockwise) the selector pawl should be raised above the gasket surface by around 1.5mm.
Later type selectors should have the pawl located approximately level with (or very slightly higher than) the gasket surface in 3rd gear position.
The 2008 genuine Piaggio spare part below has a pawl located around 2mm below the gasket surface in 3rd gear. This will not work correctly in any Italian-produced PX.
Spotting a wrong-un
The problematic EFL-type gear selector boxes have a Piaggio mark inside the casting but do not have an identifying indent hole in the wheel, only a series of ugly welds. Some of them have a threaded hole at the rear for a neutral light switch. The arm inside the ones we checked were marked ‘TVS’; which are the initials of an Indian engineering company.
How it should be
This photo using a cut-away engine casing shows how a cruciform should sit when used with the correct selector box. The selector is in third gear position. The cruciform should then line up perfectly with the shiny wear mark left on the shaft by third gear.
Bad Selector Box
This photo perfectly illustrates the problem of using a faulty gear selector box. With this one in the third gear position the cruciform is only half-way in line with the mark left by the gear.
Thanks to the following for help with this article: Harry Barlow (Pro Porting), Phil (Grand Prix Scooters), Ian (Eddie Bullet), Wolle (Scooter & Service) and the guys at ScooterCenter.com.
Now you know what to look for in a good selector box, we’ll show you how to spot wear that causes gear jumping and make old selector boxes as good as new for pennies.
Lean on me
It’s fair to say that not many road riders will lean far enough to scrape their gear selector – unless they’re falling off but racers need all the extra clearance they can get. This new slimline gear selector from French company, Liztor Racing will give racers a few degrees of extra lean.
Whether you need that extra angle on your dangle on the road or not it looks as cool as and if you own a tasty Vespa street racer it’s an extra bit of bling that you ‘need’ – even if it does cost €239. We’ll be trying one out in 2017.
We supply quality CNC Vespa selector boxes from KR Automation