Modern Vespa

Hi there,

I'm looking for some help with a brake issue I had this morning.

This morning on my way to work, my right brake lever stopped working for a minute or so. By "not working", I mean if I squeezed it, it would give no (or very very little) resistance and squeeze shut without causing the brakes to engage. The left brake lever was working as normal. Then after about a minute or so, the right brake started working normally again.

Any ideas? I don't want to be stuck in this position when I need my brakes to engage.

A couple of things can cause this, right off the top of my head:

1) Worn/leaking master cylinder seals. The brake fluid can go right past the seals instead of pumping into the brake lines. Can be caused by worn hard/brittle seals or a bit of detritus lodging in the wrong place.

2) Brake fade- if a caliper gets really hot, the residual water in the brake fluid can boil, and that vapor is way more compressible than brake fluid. This can be caused by a lot of hard braking, or a stuck caliper rubbing the pad all the time.

To remedy, I'd first change the brake fluid. Might as well replace the pads and clean the calipers at the same time. Brake fluid absorbs water and that causes corrosion, lowered boiling point, all kinds of bad stuff. It's not supposed to last forever- if it's brown, flush it. If the fade happens again with new fluid, I'd rebuild the master cylinder and the calipers.

Thanks. Very helpful.

Any idea how difficult it is to change the fluid and/or rebuild the calipers/cylinder myself with the right tools? I'm planning on changing the oil and rollers/slides soon, so I'm wondering if I could add this to the to-do list.

60cc or 100cc irregation syringe
Hose and a tee.

Push the flush up from the caliper to the master cylinder. Pushes all the air the dirrection it wants to go instead of fighting it.
Suck all the fluid out of the master cylinder first and have someone keep an eye on it when you are dong it so you don't over flow it.

Thanks, WebTech. This helps me know what I'm up against.

Like web-tech says, just push the fluid from the caliper at the wheel up to the master cylinder on the handlebar. A couple of notes:

1) if you're changing the pads (and it's a good time to do it when you change the fluid), then remove the wheel, remove the caliper from the disk (a couple of bolts), remove the pads (pins and circlips). Then wash everything around the caliper.
2) Suck all the fluid from the master cylinder on the handlebars. Only after the fluid was sucked from the master cylinder and the caliper pistons are clean do you lever the calipers open for the new pads. Then suck the bad fluid from the master cylinder again. Then re-assemble everything.
3) Do the other side.
4) Use only new DOT-4 brake fluid from an unopened can. It collects water from the air, so discard any leftover fluid after you're done. Loosen the little bleed screw while forcing the new fluid in with the syringe through the hose. Don't get any air bubbles in it- always apply pressure, don't withdraw the plunger unless the bleed screw is closed. It will leak around the bleed screw's threads- just try to keep the fluid off the pads and disk- you can wipe it up later. Keep doing it while removing the fluid from the master cylinder until it's clear and clean.
5) Do the other side.
6) Fill the master cylinder then make sure the brake is nice and hard. If it's spongy, then you got air in it and need to do it again.

One caution about replacing brake pads and flushing the fluid at the same time. I did it, and fought what I thought was air in the lines for a bit. Turned out the new pads required some bedding in, as the rotors were no longer perfectly flat. Point is, I had really mushy rear brakes, so I bled again. Mushy brakes, bled again.
Got fed up with it, took it for a ride, and within a mile of slow stop and go the brakes were fine.

Next time, I'll replace the pads. Ride for a while, then flush the fluid.