Do I have a brake problem?

[ionbeam]

Elsewhere in this thread, the metering valve has been mentioned. This is a separate component from the ABS pump assembly and a new one costs ~$175. Does anyone know what this thing does? It does not appear to have any electrical connections, just mechano-hydraulic internals...

The metering valve is in series between the rear brake master cylinder and the right front linked brake. The job of the metering valve is to set an activation threshold for the front linked brake. With light rear brake pedal force the metering valve stays closed preventing the right front linked brake from activating. This is done (according to Yamaha) to maintain 'normal feel' at slow speeds. As you increase brake force on the rear brake pedal the metering valve will open and provide linked braking.

 

[RichDoyle]

I got to pondering this and dug into my Maintenance Manual. There's this deal about comparing chassis speed to wheel speed. Ok, makes sense. But does anyone know how chassis speed is derived? I'm trying to figure out how the heck the bike could calculate chassis speed independently from wheel speed? There seem to be no kind of data input I could find that would directly support this, unless there were accelerometers built into the system (not inconceivable).

 

[Donal]

I got to pondering this and dug into my Maintenance Manual. There's this deal about comparing chassis speed to wheel speed. Ok, makes sense. But does anyone know how chassis speed is derived? I'm trying to figure out how the heck the bike could calculate chassis speed independently from wheel speed? There seem to be no kind of data input I could find that would directly support this, unless there were accelerometers built into the system (not inconceivable).

My SWAG (scientific wild *** guess) is that it compares engine RPM + gear selected and comes up with a good approximation of what chassis speed should be...................

 

[RichDoyle]

I got to pondering this and dug into my Maintenance Manual. There's this deal about comparing chassis speed to wheel speed. Ok, makes sense. But does anyone know how chassis speed is derived? I'm trying to figure out how the heck the bike could calculate chassis speed independently from wheel speed? There seem to be no kind of data input I could find that would directly support this, unless there were accelerometers built into the system (not inconceivable).

My SWAG (scientific wild *** guess) is that it compares engine RPM + gear selected and comes up with a good approximation of what chassis speed should be...................

Except the speedometer still works with the clutch pulled in and engine at idle. And you wouldn't want ABS to think you were stopped just because you did this.

The only inputs I can find to even come up with a speedometer reading (and therefore chassis speed) are the ABS wheel sensors themselves. I could conceive of algorithms that, coupled with appropriate accelerometer(s) could make this all work. But the MM makes no mention of this possible aspect that I can find. Despite an extensive discussion on how the system operates it says nothing about how chassis speed is derived.

 

[mcatrophy]

I suspect "chassis speed" is their way of describing the current speed and the maximum rate the bike can decelerate. If both wheels are braked and hit ice, they will stop rotating in a fraction of a second, obviously they've hit a slippery bit, even if they agree on the sensors' speeds. The ABS computer will recognise this.