clicking when backing up

maybe some debris in there, or the emergency brake. best to open them up for a look see

 

Is it a constant "tick, tick, tick" noise or just one loud click?

 

Each brake caliper on the Prius just sits over the brake pads, and is only responsible for squeezing the pads together when you brake.

The caliper is not responsible for taking up the forces that act on the pads from the brake rotor while you are braking. Those forces are taken up by the rather beefy bracket that the caliper is mounted to. The ears on the ends of the pads ride in slots in that bracket, while the caliper just sits over them to squeeze.

There are spring clips (known as the "fitting kit") in those slots, and they normally push the pads in the same direction they would move when braking forward, so they are already snug up against that end of the bracket and do not move or click when you make a forward stop.

When you stop in reverse, the first thing that happens as the pads squeeze down on the rotor is they get carried about a millimeter in the other direction until they hit that other end of the bracket. There's your click sound, which is entirely normal.

IIRC, there does exist a Toyota TSB for when a customer comes in who doesn't like to hear the click sound in reverse. There was at least one thread here on PC where it was mentioned, which I'm not finding at the moment. It involved some strategically placed dollops of a heavier grease, so that instead of a click! sound you could have a more aesthetically satisfying shplt? sound.

Doesn't change the stopping behavior of the brakes at all. Reminds me of the doctor who offered to write me a prescription for something to stop me from noticing a harmless condition I had asked him about.

I, for one, welcome my click sound in reverse. I smile every time I hear it, knowing that my brake parts are moving easily and doing what they are there to do.

 

I might add, that my 2006 Scion XB did the same "tick" noise when going into reverse.