"B" (engine break?) mode

Please note that "Brake fading" and "Vapor lock" is different symptom.

Regards,
Ken@Japan

 

Good point. There is at least one other way in which heat causes brakes to fade: http://www.cars.com/carsapp/national/?srv=...fade_popup.tmpl

It is good that the Prius has a "B" mode to prevent overheating the brakes.

 

OK,
Friction brakes rely upon dissipation of heat to transfer energy. In the case of friction brakes that transfer occurs to the atmosphere. Various methods of air cooling are employed. If rotors (drums) and pads (shoes) accumulate heat faster than it is dissipated, braking will then become an exercise of 'squeezing' pads on rotors to little or no avail. I have experienced overheated rotors, pads and vaporization of brake fluid simultaneously. Result....you get a spongy pedal which though mashed down as hard a possible, leads to no decrease in momentum....a very uncomfortable situation indeed.

 

Does anyone know if using the B mode will cause excess wear on the tranny or any other part? I never use to downshift on manuals trannys because I was told it was hard on the clutch. I've only used B mode a couple of times and that was by accident in a parking lot. I thought I left the emergency brake on! I'm a little nervous about using the shifter while going downhill at high speeds I guess....

 

It shouldn't. It doesn't move anything in the transmission, it just tells the computer to spin up the engine and to regen more when you lift your foot off the gas. There is much more torque and stress put on the transmission from accelerating than using B.

 

This was my best post explaining B.

B under the D in the Drive gears? | PriusChat

One answer to the question "Why does Toyota include a B gear?" is that they are legally required to.

Standard No. 102; Transmission shift position sequence starter interlock, and transmission braking effect. - Federal Motor Carrier Safety Administration

 

Every month I make an 160 mile round trip which includes a summit and downward b braking. In the b mode the car stays at 65 going down the summit side of the trip both ways. With 198,000 miles my battery for the engine(not the 12v) is still running. I hope that the constant recharge of the battery on the trips up and down the mountain keep it charged. I wonder if the batteries that died sooner than others used the b mode. If not maybe using the b mode would extend the life of the main battery.

 

Hmmm... So far I've only noticed that the hv battery life for cars in very hot climates seem to be a little shorter. I live in a city of 100k with one Toyota dealership and they've only seen one gen 2 with a bad battery. The city north of me with a pop of 40k has never seen a bad gen 2 battery. This being up north where summers can be hot for a few weeks and the rest of the year fairly moderate...