Modern Vespa

Hello 2t vespa fans. I have a pk 50 with about 5000 kilometers. Whenever I ride uphill, or when the is a lot of weight on the engine and gearbox (mostly on 4th gear) the gear fails for half a second or less. It is like pulling the cluch really fast while driving. Any opinions about the problem? Is it some broken gear teeth? (info I have a bad clutch)

Sounds to me your shifting cross needs to be replaced.

Shifting cross and possibly worn 4th gear. It will require the cases to be opened up.

Maybe the gear cables are too tight so they put pressure on the gear selector while sitting on the scoot…

Having experienced similar issues, I concur with SaFiS on this. Also because time and again Vespas have proven to me that on a standard scooter the simplest possible problem is the most likely one...

Even if it was originally the gear cables, now that it's bashed the cruciform and gears around for a while, the cruciform and possibly gear will need to be replaced in any case.

Why does it only happen uphill or with weight on it? Wouldn't it show more often if it was just a cable issue?

my smallframe did this. in one case it was because i had tuned it and did not get a strong enough spring in the selector. i think the other time was cables. if you don't get the pressure on the selector it can pop out. cables are a likely source, well worth checking.

Advice I was given to keep the selector in place was to keep the standard spring, but add an extra ball bearing. I did that on the Smallstate and it's never had problems staying in gear.

The other piece of advice from Matt & Dave was to assemble the whole thing in a clear plastic bag so when (it's a "when," not an "if") a ball bearing or the spring go flying, you won't lose them.