2012 Prius: Weird Dragging RL Caliper


Hey Scotty,

I got a really weird dragging caliper issues and whatever troubleshooting I tried nothing seems to work so far; there's a ton of details from troubleshooting so bear with me. I bought a 2012 Prius (about 84k miles), soon I realized the rear calipers were seized for good on the RL side. I ordered Raybestos E3 calipers, rotors and some good pads to go with them from RockAuto.

I changed the calipers, but RL got a bit hot when driving; drags a little (I get maybe 1.5x turns of a wheel when hoisted vs 3x turns out of RR which is working fine, the disc gets warm but I can touch it after driving without any issues - or even stays cold in the winter). I changed the flexible line to rule out an issue there (and the hard line after because of rusted nuts). I checked with a comparative dial clamped on the caliper's bracket if the disc is warped, and I checked the travel on the caliper's cylinder/piston (got 0.08mm on the disc, and 0.35mm travel on the piston, seems good from what Priuschat community says, right or wrong?). I checked if the pins are lubed so many times, if the caliper's cylinder sits flush on the pad (ie not riding the pad's pin, for the hand brake system), I bled the brakes quite a few times double checking using Invalid Mode (Toyota's way of disabling the electronic brake system). To no avail.

Toyota had changed my booster under their extended warranty program right after this repair. I checked with VXDiag dongle and pirated Techstream (watching live - I got a YT link for that: https://www.youtube.com/watch?v=uqCI1rwxifs&ab_channel=AndreiFasola - AND if you look there you'll see the comparative dial tests and a couple more) to see if the actuators are working properly - so it seems from reading the repair manual and after discussing the data with a coupe of knowledgeable folks on PriusChat.

If I take the caliper off and spin the wheel, it spins well, smoothly, freely (I get 8-9x spins without even trying) . So it doesn't seem to be the bearing. It's the pads rubbing against as soon as I depress the brake.

So. Now I exchanged the calipers under warranty with new ones - thinking there's an issues with the caliper - and RL still drags so it can't be the caliper, no way. I used Permatex copper anti-seize and AGS sil-glyde to lube the calipers btw.

One important detail: when I took of that RL seized caliper, I accidentally forgot the key in my pocket and I pressed the break like stupid while the caliper was off the rotor (somebody did it and I wasn't aware) and the cylinder went all the way and I lost a lot of brake fluid along that problem side (the fluid was gone in the brake fluid reservoir).

So I looked online and found out about master bleeding and this guy was saying that I don't even need to unhook the master, all I need to do is to connect the caliper's bleeding point to the reservoir with a long hose and I'm going to bleed out all the bubbles in the system. I did that thinking that "yeah, short circuit, long circuit, same thing". So I did it for 45-60min to make sure I get all the air out.

And I thought it did the trick. And I say this only because the other brakes are working fine and are not overheating (they are luke-warm to warm if at all).

So THAT master bleeding is the only thing which I did that I don't have a lot of faith in. The rest, I was as careful as a surgeon. And I wonder: could it be some air stuck somewhere? If yes, how???

Am I missing something?

I am going crazy. Sorry for the long post - too many details. If you have any idea: please enlighten me! Thank you.

Andrei from Montreal.

Comments (2)
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Scotty Kilmer
Scotty Kilmer


You should learn to be a bit more To the point. What does hybrid cars are extremely complex I would pay a guy with a Toyota previous deal I level scanner to analyze the breaking and regenerative electronics. Though sometimes it's a simple as a collapsing brake hose