Rear Left Prius Brake Caliper Seized

Change calipers in pairs. Both front, both rear. And you should do a brake fluid flush.
That's why they seized, it's probably never be flushed.
Get some course grit sandpaper and sand down the disc's. It's hard to tell from that photo if there
is a lip or not. If there's not, you should be okay with just the sandpaper.
Go easy on the brake pedal the first 100 miles or so so they can "seat" in.

If you can use compressed air to get the puck out, you may be able to rebuild them.
It will depend on how badly pitted the caliper wall is. If it's not too bad, you can use some super fine steel wool
to clean it up. The repair kit will have a new piston seal and dust cover.
Soak it with rust penetrant and maybe try pushing it in a little. You may have to go back and with air and
pushing the puck to get it out. The rubber seal has glued itself to the wall.

I've done it on MY vehicles. I would not risk it on a customer car because they wouldn't drive the way I would.
If you don't feel comfortable with that, then get new or remanufactured ones for peace of mind.

 

I had rear brake problems a few years back; the rotors had scoring and a zone on the inside face with next to no contact, and consequently a lot of rust. I removed the calipers and scrubbed them with steel wool. I think a better job could be done though, with a conical wire brush wheel on a drill, for example. To remove the rotors if they're really rust-glued on, there's a pair of threaded holes that you can screw M8x1.25 bolts into, to pop them loose.

Anyway, with new pads, the rear brakes were very noisy at first, but within a week were back to normal.

I would recommend to just visit a Toyota dealership parts department.

Have a read through this, it might apply to your situation:

Regen Braking should save the mechanical brakes | Page 2 | PriusChat

 

Wow. I just changed my LH rear caliper last Thursday and my old rotor looked exactly like your picture. Except my caliper wasn't seized. In my case, the upper brake hardware was loose which caused the pads to get stuck/seize. I needed to replace the caliper bracket but I ended up replacing the whole caliper instead.

I ended up buying a Raybestos Element3 Caliper because it is not remanufactured, there is no core charge and it costs less than the OEM caliper bracket. Beware as the Raybestos Element3 caliper piston head face is different than Toyota OEM piston face. I can still retract it but with a different side of my Isle cube tool.
Catalog

I am also in Canada, but I ordered my caliper from RockAuto. I bought a bunch of other parts to offset the shipping. My family was going to the US anyways and picked up the shipment at mailbox at the border. Although, you can now directly ship across the border.

 

You'll also hear of using brake fluid, or even a grease gun, to force a stubborn piston out. Advantages are, you can often get a way higher pressure out of a grease gun than an air compressor, plus, because the fluid or grease doesn't compress and store energy like air will, the piston just goes plop when it finally comes out; you haven't built a cannon.

If you search for the Toyota caliper part number with -84 tacked on the end, sometimes you'll find a Toyota-rebuilt one available. They do a good job.

 

Raybestos FRC12542N came pre-assembled with the caliper mounting bracket, so it has guide pins and boots.
1) Caliper
2) Caliper bracket
3) Guide Pins + bolts (the bolts on there very tight out of the factory!)
4) Upper and lower brake hardware that goes on caliper bracket (but missing vibration clips that hooks on to pad ears)
5) Two copper washers

No replacement banjo bolt. No "V" shaped anti-vibration clips that go on the brake pad ears. I paid a mechanic to install so I don't know if there are bushings at the bottom of the guide pins.

Beware. The piston face does not match Toyota OEM. It looks like a flat clover rather than a the Toyota propeller. See picture on their website:
https://www.brakepartsinc.com/.imaging/mte/raybestos-theme/catalogProductImage/image-catalog/catalog-images/FRC12542N/Images/FRC12542N_BAC.jpg/jcr:content/FRC12542N_BAC.jpg
OEM:
Toyota-Prius-Rear-Brake-Pads-Replacement-Guide-028

The pictures for FRC12542N on RockAuto are wrong. Actually, the Raybestos website shows all the parts quite clearly in the 6 photos. Click on the "catalog" link below:
Catalog

The reason I bought this caliper is because it is not remanufactured and it has no core charge. It also cost less than the $188 OEM caliper bracket or the $255 OEM caliper assembly from my local Toronto dealership. You need to factor in shipping costs and taxes before deciding. Of course, I bought extra rotors and pads too to offset the shipping. Don't forget to apply the 5% RockAuto coupon (if you can find it).

 

Not sure about "flat clover" mention by @Siward. Does it still lock on the pin on back of inner pad? The cross pattern on piston face, locking on that pin, is mandatory to prevent the piston rotating when parking brake is applied.

More info in my previous link.

 

I just did this as well at 165,000. I went to a local Napa store and replaced the LH caliper. The list price was half of the Toyota dealer. I was able to visually match the caliper. Topico brand? When you button it up you can turn in your old caliper for a rebate. I got a couple of qts and flushed brake fluid. My rotor was like yours so I replaced both rear rotors and pads. I selected the favorite rotors and pads on Rock Auto. 10,000 + miles. All good. Got new tires for the winter and had them double my work. All good.

 

Clover-like piston face for Raybestos Element3 FRC12542N. It is also more flat than OEM. Yes, you need align the pin on the back of the brake pad shim to fit in the gap.

 

Looks effective.

 

I took that approach with a Gen 1 caliper and the experience dragged me into a whole exploration of finishes on brake parts after I saw how many weeks (yes, actual weeks, countable on one hand) the sharp-looking highly-touted "exclusive rustproof" coating on the aftermarket caliper actually held up.

Granted, those were Gen 1 front calipers, cast iron. I believe the later generations to be aluminum, at least in front. Not sure about the rears. The brackets are still ferrous as far as I know.

Aluminum construction surely changes the finish story somewhat, but the basic takeaway is still with me: it's no problem for the finish on an aftermarket part to look awesome in the box, on the shelf, or on the webpage.

 

Use what you got!
Grease is messy and harder to clean out. Brake fluid would also be messy.
But if they work, they work.

There are many options available. Just pick one that you like best.

I used air because it was available.

 

There's a stubby pin on the pad back, that locks in between the spokes. Looks like it might work with that alternate.

Do check out the price of OEM caliper too. Might be sticker shock, but doesn't hurt to ask.

Is it a done deal that the caliper needs replacement??

 

Nothing wrong with cutting corners, as long as you don't cut safety!
Replacing all calipers, pads, and possible rotors, and flushing the brake fluid should give you
a safe braking system, and peace of mind.
Using the brake paste and grease should keep things from rusting up again.

 

Are you ordering from RockAuto? If so, I would suggest to consider buying the brake piston retractor cube (if you don't have it already) or the cheap Dot3 brake fluid only provided you can get it to ship from the same warehouse. It could save you a few bucks.



Brake & Wheel Hub Tool Disc Brake Piston Tool Parts | RockAuto

The cube costs about $13 in Ontario. It is only worth getting if it comes from the same warehouse as your existing order. Buy it locally otherwise.

Brake & Wheel Hub Fluid / Chemical Brake Fluid Parts | RockAuto

The US prices auto parts are always less than Canada. The only deterrent is shipping.

 

Just for a data point: I get Toyota DOT3 fluid for 7 something a pint, through dealership.

I use Sil-Glyde Brake Lubricant on pins, and Permatex Anti-Seize on pad backing plates, shims and caliper contact points.

It's frustrating what can happen to AC systems, the mold issues. Especially considering the insane measures needed to open up the dash to get to it.