2015 Prius 2 rear caliper piston won’t retract

Make sure you have it aligned so the pin on the face of the piston is at the 12 o’clock position. That little pin goes into the back of the brake pad. If you try to slip the pads over the rotor without the pin aligned correctly, it will never go on.

 

RU saying that you can't get the piston in the brake caliper to retract fully so, with your new pads installed, there's no longer room for the rotor?

Maybe the brake fluid has absorbed water, expanding its volume, preventing full retraction of the piston. Old pads/worn rotor can cover up an increase in brake fluid volume whereas closer tolerance with new pads/rotors.

 

Welcome to Prius Chat .

Not sure on the 2015, but the 2010 you had to have the dice tool to retract the piston in. Is that what you mean by turning it in?

How many miles before this brake job?

Good luck and keep us posted .

 

Are you using the tool the spins and compresses it? Or are you just spinning it?
They too, which you can rent from autozone, is threaded so it presses it in as it spins it.

 

I’d wait for the dice and regroup .

The emergency brake shouldn’t matter for setting the pads and calipers.

 

Do you have an auto parts store near you?
Autozone, discount, Orielly's? etc. They have tool rental, it won't cost you anything because you get your money back when you return it.
That tool presses it in as it turns it.

 

It sounds like the internal screw mechanism is not engaging properly, for one or more of the reasons mentioned above. Every turn should retract it a little. Just to ask the dumb question: you are screwing it in clockwise?

Yeah use the proper cube, and maybe you just need to press firmly to get it started, it's not threaded in??

Also, I'd concur, it's not necessary or helpful to disconnect the parking brake cable (aka emergency brake). I've had the rear brakes open a couple of times, and I just have the parking brake release, and pull the caliper assemble off and away, tie it with some twine.

Do disconnect the negative cable from the 12 volt battery, whenerver you're doing stuff like this. When you're DIY'ing without Techstream, it's your safety net: it's possible for the hydraulics to start pumping, pop out a piston. Maybe more so with the fronts but who knows.

Also, the piston should end up with the cross pattern of spokes on it's face oriented like an "X", to fit properly with the stubby pin on the back of the brake pads. And when reassembled, pump the brake pedal multiple times, make sure everything's well seated, tightly locked together in that orientation. It's very important that it goes together thus, and stays like that. Each time you apply the parking brake the piston with attempt to turn, and that pin locked in the cross pattern prevents that from happening. Important: if the pin does manage to ride up on a spoke on the piston face, you will have problems: steady brake drag and uneven pad wear.

Anyway, here's some brake info from the repair manual:

 

2 years ago I kept reading on here that if the pistons protrudes because you open the driver door while the 12V bat was still connected, you needed techstream to get it to retract back in.

 

I 2nd this, we did this to mine last year at the meet up w/parking brakes will on.

 

Which side is it on?
One is a left handed thread. Have you tried turning counter-clockwise, and pressing it in?
It won't hurt to try.
My kit has both left and right handed threaded rods.
So I think that is your problem. Try your little square again, but this time go counter-clockwise.
And press as you turn.

 

My manual only says clockwise, nothing about the sides being different.

 

The first time you try to start it after pulling the negative lead, you get all the lights .

Try powering it up a second time and then see if any lights appear. If not, you’re good to go.

Glad the dice did the trick.

 

I see someone said the notch in the rear caliper piston had to be in the 12 oclock position is that correct? I am having problems with the rr pads but I have been putting the notch in the 6 oclock position. my prius is 2012.