Left rear brake rotor groove

Hmm isn't this usually caused by the incorrect positioning of the parking brake pin on the piston? It is essential that the pin is aligned correctly or you can see problems like this.

 

I got grooving on rear disk, after doing my own rear brake inspection, and neglecting to get the caliper piston oriented correctly, so that the stubby pin on back of inside pad is between the spokes on the piston face, and well seated thus, so that it can't slip/jump, say when you apply parking brake.

Have you had a brake inspection, where the caliper was pulled off? Who did it? How long ago?

If the piston has rotated, so that the pin on the back of inner pad is riding up on the piston's raised spoke pattern, you will get significant/constant drag, bevelled pad wear, uneven contact between the brake pad and rotor, and so on. The piston, instead of applying uniform/full pressure on the back of brake pad, is bearing only on the pin, messing everything up.

To check:

1. Feel the rear wheels after a drive, see if they're hot.
2. Chock front wheels, raise rear of car, and try spinning the wheels with parking brake off. They might have slight drag, but should easily spin a revolution or two without a lot of effort.

To remedy if this is the issue, and it might be best to start with fresh pads:

1. Ensure piston is oriented like a letter "X" (see attachment) when reassembling:



2. Tromp brake pedal multiple times to firm up brakes, ensure they're well seated.
3. Reconnect 12 negative cable. (should be disconnected at outset, to ensure no accidental pressurizing, which could pop the piston out.) Do not use parking brake.
4. Go for short test drive, gently using the brakes.
5. Upon getting back, gently apply/release parking brake several times.
6. Chock front wheels and raise rear, release parking brake and check wheel spin is near-free.

 

looks like rock got lodged in between your pad and rotor

 

Could be a rock or something, I would pull the pads out and see what’s causing it.

 

Before any disassemble, try turning the wheel. If it's really dragging I'd put money on misaligned piston, which you can determine when you open it up. The inner pad will have bevelled wear, and the pin on backing plate will be chewed up. The piston pattern too is a tip off. Also, the inner face of the rotor will be only 50% used, the rest likely rusty, if there's been any rain to speak of.

 

We wait...

 

Are you saying the wheels should spin more freely after this process, or the same as before?

 

Yes. If you have the pin properly positioned, between the caliper spokes, the wheel should easily spin a revolution or two. If misaligned it will fight you.

 

plus make a lot of grinding noise

 

When I had that condition I actually didn't have any noise, and when I remedied it, got the alignment fixed, then I had noise, for the next week or two, with every brake application, getting the previously unused, rusty zone of the rotor back to snuff.

 

My 2012 is a refresh and at the last meet up, I did rear caliper pin lube. There was no pin on either side to align, verified this with Raytheeagle as he was there. Think the 2013 won't have pins either to be aligned, could just be a rock stuck in between.

 

This is the pin, at least on mine:



Both inside and outside pads have them, though it's only the inside pad (the one against the caliper piston) which uses the pin, to prevent the piston from rotating when you apply parking brake. I ended up replacing my rear pads, invoice dated Aug, 2014, the parts numbers for replacement pads was:

04466-76012

Looking up a 2012 Prius on McGeorge Toyota, I see this (supersceding) part number for rear brake pad:

04466-47080

Googling that part number, I find this image:



Which looks to have the same pin. If it didn't, the piston would be free to rotate, and screw itself outwards, when you apply the parking brake. The intent with the pin is to lock in between the spokes on face of piston, prevent this rotation.

As far as I can see, the only modification in the new pad is a greater bevelled area, which I believe was a half-hearted attempt to quell brake squeal some owners were noticing, just at start up, often when reversing.

 

There is a pin where you need to align the caliper to the brake pads, I see it on my 2012 Prius when I was filming too.