Test drove today.. Questions for people who know.

I did look at the brake linkage this morning and there appears to be a physical rod that goes through the firewall from the brake pedal into the back of the master cylinder. I have no idea if that's connected to the piston in the cylinder and can produce fluid pressure by itself, or if it requires the electronics/motors to build pressure. Hopefully some of both, with normal braking function requiring the electronics/motor but with a fail-safe of a mechanical connection as a last resort. The diagram posted by @insightman from @AnthonyW doesn't seem to explicitly show the mechanical connection. Further, the parking brake is operated by a switch and a motor, not a mechanical linkage operated by the driver. So in an electrical failure of any type (fuse, switch,motor, wire, etc), or a mechanical failure of the mechanism, you are SOL with the parking brake. I'm going to cc this post over to the Brake Issue thread too.

 

I'm certain that like all current automobiles, the Clarity's braking system has redundancy. However, I've never heard of a brake pedal going to the floor in a modern automobile, which makes me wonder what happened. Here's the diagram from the PDF document. It seems to me that the rod attached to the master cylinder must be connected to the brake pedal. If there was an intermediate device between the brake pedal and the master cylinder, I believe it would be part of this diagram. I don't see any redundancy in this diagram and I don't know what the "motor" and "gearbox" are in the braking system.

 

The 1998-2007 Toyota Land Cruiser uses a motor-driven booster pump in the ABS accumulator that builds pressure in the brake system. If that motor fails (and they have), the pedal goes to the floor and the vehicle acts as though it has a complete brake failure. There is, however, a completely mechanical parking brake for the rear wheels. And, I believe it was in 2012 that Subaru issued a stop-sale order on their Outbacks for at least a short time because of a master cylinder defect that resulted in a complete loss of brakes and no pedal. So, not unheard of to lose brake pedal action, but thankfully rare.

 

I use the paddles in that situation so my leg isn't in one position for a long time, pushing constantly on the brake pedal. I've gotten minor cramps that way on long road trips going down steep mountain ranges. I really don't worry about brake wear at all. I know that >90% of the stopping from the brake pedal (assuming a normal stop) is from regen so we'll probably need to replace the brake pads every 15 years or so.

 

Actually, I haven't on long downgrades. That's a good tip!