Modern Vespa

This topic seems to be as old as modern Vespas, and up to now, I thought I know how to fix it: clean the transmission case and the clutch from dust.

Well, I am sure we cleaned Salima's GTS (under 5K miles) very diligently, with compressed air, and completely, but the sea lion is back.

What else could it be caused by? The tranny generally looks clean, no oil or anything else that could cause slippage.

Is this even something we should worry about? Or just accept it as proof that the clutch is doing its job? It mostly happens at non-WOT starts.

Glazed clutch shoes cause it too, along with a highly polished bell. If you give the shoes and the bell a quick once over with some emery paper, all shoud be sorted.

Yup, sometimes you just have to persist. For a while I felt like it was recurring every 3-5k. Now it hasn't happened for 18 months/10k. I agree with the glazed clutch pads. Get the cover off and abrade the surface and the clutch bell housing with 180 - 250 grit carborundum (we call it Wet and Dry) paper.

+1 on the glazed pads. I like a little 200 grit sandpaper on the shoes, and some scotchbrite on the inside of the clutch bell.

I'm not too sure about the strangling though. Defo on the sea-lion though but more of slightly drunk sea-lion in a sea-lion karaoke bar trying too sing. and it's singing.... P---ii--aa--ggiiiooooo......

No, our sea lion isn't drunk for sure. More like drowning, while he sings pe-aah-dgo. (with a short o, like in politics).

Hint: our sea lion is Italian.

We'll give him a good rub with a 200 towel when we see him again

The sound is probably caused by vibration of the clutch pads, hitting against the bell. If you have the mentioned glazing etc some slipping might occur just when the clutch is engaging, and this slipping will tend to bend the shoe away from the bell, rpm goes up and it tries to engage again. From the song you could analyze the frequency.

On the Master 460 the clutch was changed from 3 to 5 pads, probably to decrease the inertia of the shoes the gain a more positive engagement.

In the old days when the drum-brakes on a moped were screaming we would chamfer the leading edge of the shoes, and maybe cut one or two groves across the friction surface, for dust removal. This would be easy to do, once you are in there cleaning, at least it shouldn't do any harm.

This is just my theory. My BV seal is occasionally singing, when the three-shoe clutch is hot but I haven't tried this fix yet