New Rotors at 45k??

New pads on an old disc definitely should be bedded in as the discs can be grooved and ridged. If you do not bed in it can lead to very poor brake performance in an emergency stop. With new discs and pads because both are machined flat they bed in very fast but it is still recommended.
Some pad manufacturers put a coating on there pads to promote faster bedding in.

 

I have in the past cleaned the discs when they are smooth but rusty by jacking up the car on one side only, and removing the wheel putting the car in ready and drive ( with parking brake on and wheels chocked)then cleaning the rotating disc with a wire brush and emery cloth. The lug nuts should be put on to hold the disc in place, however great care is needed to avoid the rotating lug nuts. Do this at your own risk, but it does work. An angle grinder with a flexible disc also works well but the disc (rotor) must be rotating to avoid flat spotting the disc. This only works on the outside of the disc as you cannot get to the rear face.

If the discs are below or near 20mm thick (23mm new) or badly scored or ridged I would change them, since they should then last at least 150,000miles.

In the UK a good source of discs is Ebay. Try to stick to well known brands, being from the UK I do not know what those are in the US, but in the UK there does not seem to be any quality issues with discs I have bought and all seem as good and sometimes better than OEM.

I recently replaced my own front and rear (UK Prius has discs on rear) for a total of £57/$90 OEM's were £400.

Hope this helps.

John.

 

The rotors do not look to bad and will be ok for further use. The black spots are rust polished in to the rotors. Looks like you have lost the use of a 1/4 inch of the outside edge, this will not clean up with use and will machine that portion of the pads away immediately.

A light regrind no more than 1/2mm (20thou) per side of each rotor would be good if you can get it done at a realistic price but would probably be cheaper, quicker and more economical in the long run to replace rather than regrind.

You do not report on how much pad was left if 2mm (80thou) or more I would run these as they are for another 10,000 miles and maybe more dependant on pad life left then change discs and pads. On the Prius in normal use it is reasonable to expect 10,000 miles per/mm of pad thickness.

If you just fit new pads to the old discs bed them in well, you will know when they are bedded in when the brakes feel good braking from 50mph quickly in neutral.
Hope this is of help, and do not forget the precautions before you start the job as apart from the difficulty of bleeding if a piston pops out I would hate to think what it would do to fingers if they were in there at the time. Do not let this put you off doing it yourself just be careful.

John.

 

My diagnosis is excessive rust caused by road salt left on the rotor. It looks like the salt wasn't regularly washed off of the car. It is a good practice to wash your car weekly when salt is spread on the road (cheap insurance). I've never seen that much corrosion on an 07 with so little miles. Like Brit said, the black is rust ground into the metal. I agree with him to change out the rotors but I would DIY. Some times you have to bite the bullet and that is the case here.

 

So the dealer was completely correct in the first place. Sounds like a keeper.

 

Yikes I did not realize the rear pad footprint was so much smaller than the front. Good job on the brakes most people bone that up.
Be aware the weather really attacks and rusts new rotors on a Prius since so little use. Get in the habit of putting the car in neutral and apply the brakes. In neutral no regen brakes only. Just a little firm pressure now and then like on slight hills. Really helps keep the rotors clean. They'll still look like crap compared to reg front rotor but will not get as bad as yours.

 

Congrats on a job well done, and your brakes should now last you 100,000+ miles. Follow what many have said and use the brakes in neutral on occasions to keep them clean you will not measure the extra wear.

The corrosion on the back of the discs looks very much like mine did but at 80,000 miles I even contemplated removing the dust shields.

My UK version of the Prius has discs (rotors) on the rear and while I have no problem keeping the fronts bright and clear the rears are milk chocolate brown colored after 8000 miles but smooth and shinny. The rears do to little work to keep clean.

John (Britprius)

 

The drums do not suffer with the problem as when the vehicle is parked with the parking brake on the surface of the drum is 90% sealed by the shoes in contact with the drum.

 

What really really helps is wheel covers if the car has to stay outside. The brakes will start barking really quick with new rotors left outside. There really cheap and go on fast. They keep all the moisture off the rotors & wheels.

 

No cloth covers. They have vinyl on outside and soft inside. They fit right over wheel. Keep entire wheel assy mint clean. Down here in Fla everything is soaked at night and it rusts the rotors bad. Like these:

eBay
Jc Whitney

Set of Four New Wheel Tire Covers for Use on RV Trailer Truck or Car | eBay

 

Everyday. Takes 30 seconds to take off.

Driving does little in a Prius to clean the rotors. Must release regen and therapeutically apply brakes to clean them. They rust while the car sits overnight. Boston like Fla is wet at night.

Just mentioning it to you because your going to be very bummed when you see how fast your raw new rotors are going to get rusted. Look at your rotors tomorrow morning. Cloth wheel covers will fix that I promise you.