Modern Vespa

As the title says the scooter has begun wobbling when I release the throttle. Very disconcerting especially on corners. Also rear brake working intermittently. Sometimes you squeeze the handle and get nothing, release it squeeze again and get a little braking. Release, squeeze again and get full brake!

Just putting this out there for the GTS geniuses to help me solve the issue. Cheers

You have air in your rear brake line.

Check your tire pressure for the wobble. Many others have discussed cause and solutions that worked for them.

It could be a warped rotor that is pushing the pads back into the caliper.

I bled and replaced the rear brake fluid (twice) and it was still happening.

I'll check tire pressure re' wobble.

It might be this. Do u no how to resolve it?

There is a tool to check it. It's called a dial indicator. It mounts to the swing arm and has a pin connected to a dial that measures the amount of variation in the surface of the rotor as you turn the wheel. If it were out of tolerance on a car you might be able to turn it flat on a lathe but on a scooter it would probably mean replacing the rotor.

The wobbling that you mention could also be caused by something being worn or loose in the rear suspention or a wheel bearing. Is there any play side to side or up and down on the rear wheel when it's on the center stand?

Hope it's not the rotor then but I really am at a loss regards the brake problem.

There's no play at all on the rear wheel when the scooters on its stand.

If there is a bubble in the line, the lever will be consistently mushy after waiting a short period of time with the scooter stationary.

A wobbling feel is likely to come from the front. ( Tyre Pressure)

A weaving feeling will likely come from the rear. ( Tyre pressure)

Put the front break on and rock it back and forth.Any play in front end?
Loose head set bearings or bad?Im just saying that because I'm not sure if your talking about front or the outher end.

I genuinely think its tire pressure as I used a dodgy pump last time I checked and I felt at the time that what I was putting in seemed excessive. I'll be checking again later with more reliable pump and gague.

My wobble came from the back, weight had come off rear rim.

I would check out the tires , pressure, rotor ... but at the end of the day the 300's whobble which is why i sold mine.

If you take your hand off the steering wheel decelerating at low speed's its always present or at least on mine. Couldn't stand it.

My bmw 1200 gs also had an issue with always pulling too one side if you took your hands off the wheel at any speed. Sold that too.

Hope you resolve the issue and have better luck with your 300 than me.

My 300 does not wobble, regardless of pressure in tires. All the way 1.8 to 3 bars tried.

But I would say it is not the most "stable" ride I have had. But, that is what makes it fun. It is lively and really fun to drive. Maybe not for 2 hours on a freeway, but still. But it does not wobble, mine that is.

The brake issue, a warped disc/rotor I would have thought you would feel, pulsating lever when you use the brake. Good luck, I know how frustrating these sorts of things can be.

Oh now I got to think about another thing here, could it be that the tires have worn "flat" they are not round anymore? You get a bigger contact patch, that can seriously mess up handling in general.

Weights are applied for wheel balancing on the rotation axis.

Wheel balance is not noticed as "wobble" ie lateral shaking movement.

Front wheels can wobble because they have a steering axis to pass lateral movement through.

Rear wheels are fixed laterally via a fixed axle. The balance weight does not affect that.

Two wheel machines do not exhibit wheel alignment issues that 4 wheel vehicles do.

What's the mileage? how did you bleed the breaks? Might want to invest in a mighty vac. Think back to when the problem started. What did you do differently than normal.
Good luck.

Rear wheel was loose. Stripped the lot off checked the brake calipers which also gave me a chance to check the shoes/pads. All fine and back together snug as a bug. Not tested yet though as I'm waiting on an oil filter but I reckon the dodgy loose rear wheel is the culprit. Will let you all know after test ride so fingers crossed

I'm more concerned that your scooter and motorcycle had steering wheels!

Touche ! That made me laugh

Me too, thanks for the chuckle!