On changing the brake pads in my 2010.

Think that’s overkill, i uncapped the brake cap on the brake fluid resivoir so the fluid can move freely when pumping the brakes. The level rose pretty high, Ray the eagle, sfo and I went whoa looking at the level.

 

Yep, I perform that experiment frequently, with the same result. Dumb that it runs needlessly so much.

 

If pump has recently run, and you haven't done a "zero down" before checking the fluid level, a lot of the fluid is in the accumulator, not in the reservoir. Pumping the brakes will use the fluid from the pressurized accumulator and return it to the reservoir.

The main level markings on the reservoir are meant to be read after a zero down. With new pads, and zeroed down, the MAX line is the right level to have.

 

?? But pumping the brake causes the pump to re-pressurize the accumulator, even if the door hasn't been opened and the fob is far away. Therefore to "zero down" would seem to require waiting a few days for it to leak down, or pumping the pedal with battery or relevant fuse disconnected.

 

It's easiest using Techstream, as directed in the manual:



("After the booster pump stopped" is, I believe, a translation glitch; when you request zero down, what you hear is of course not the pump running, but the fluid hissing out through the opened solenoid valves back to the reservoir.)

Without Techstream, yeah, you need to cut power or enter invalid mode, then pump the brakes a pile of times. Manual says "40 or more", but really, you can easily tell when there's no accumulator pressure left. You'll have normal brake pedal feel for 20 or 30 or 40 strokes and then the next one about breaks your foot.

Bit of trivia: this method works for Gen 1 and Gen 3, but not Gen 2. Gen 1 and Gen 3 use the fluid pressure to boost your pedal pressure, using an actual hydraulic booster behind the master cylinder piston (which is why there's such confusion potential when people also call the pump/accumulator the "booster"), but Gen 2 was a different, much more by-wire approach. No such chamber in the master cylinder, and your brake assist comes completely from the ECU's application of the pressurized fluid to the wheels. So just pumping the brake pedal with the power off does not zero down a Gen 2, nor is the pedal feel different when zeroed down.

 

That's mostly going over my head, no Techstream, but I think it's related to what I observe:

If I go out to the garage in the morning, open the front passenger door and pop the hood, check the brake fluid level, it's quite high, I believe a mark above MAX (IIRC). Then, if I open/close driver's door, the pump whir starts, and the level in the reservoir drops a good 1/2".

 

Right ... if there's enough internal leakage that it sort of self-zeroes-down overnight, then the fluid level will be high in the morning, and then the pump will run and stuff it back into the accumulator, making the reservoir level drop.

It's still possible that the overnight leakage rate only partially "zeroes down", and if you did a real zero down the reservoir level would go even higher.

It's supposed to be at MAX when zeroed down and just starting with new pads. As the pads wear it will go lower, and whenever not zeroed down it will be lower.

If you're seeing it above MAX in the morning, that means that at some point somebody checked the level when the pads weren't new, or when it wasn't zeroed down, and said "schezbzflat! I need to top this off!" and now it's a bit overfilled.

Fortunately, there's enough room above MAX in the reservoir that probably that won't lead to an overflow mess, unless it was topped off at a pretty worst-case time (like, the pads were very worn, and the pump had just run).

 

My apologies if I'm posting to the incorrect forum. I have a 2010 Prius with 236k miles. I personally just replaced the front rotors and pads, and cleaned and re-lubricated the caliper slide pins. Everything is back together and appears to be working fine after driving for approximately 50 miles. I'm now ready to do the same to the rear brakes but am now very hesitant to do so. I have been reading, watching (YouTube), and have been hearing all sorts of conflicting information regarding the rear brake service. It has been suggested that doing a DIY rear brake service is significantly more complicated than the front, and that using a rotary pressure tool (I own a kit) to force the piston back into its housing can severely damage the rear brakes. Its also been said that you should open the bleeder when turning/compressing the rear piston as well. Supposedly opening the bleeder valve then requires bleeding the whole system which I was not prepared to do. Another thing strongly recommended by a mechanic is that the vehicle MUST be placed in another "mode" (not maintenance) while working on the rear brakes and the car must remain in this mode while doing the work.

Is there any merit to all of these things I'm reading or is it just as simple as doing the front brakes? I do understand the rear brakes have the parking cable attached. If need be I can certainly return the parts I've purchased for the rear brakes and schedule an appointment.

Thank you for any feedback on this topic.

 

I would prep the car for rear brake service same as I do for front: disconnect the negative 12 volt cable from the post and isolate it (say stuff it in a heavy rubber/leather glove). Lay the other glove over the hatch threshold locking mechanism, then lower the hatch gently onto it.

I've never opened bleeders when retracting pistons for new pads, and I have replaced the rear pads on our 2010 (long story). OTOH, I have bled the brakes tri-yearly, following @NutzAboutBolts video (link in thread at top of this forum) and repair manual isntruction (Invalid Mode method, see attachment).

Like a lot of rear disk brakes, you need to screw the piston in to retract it. There's a cheap "cube" tool with various protrusions you can mount on an extension on a ratchet wrench, makes this very easy. Or in a pinch needle nose plier tips. But I would use the tool.

You screw the piston in clockwise as far as it'll go, then back it out slightly if needed, to get the piston orientation like this:



The shaded zones on the piston face are raised spokes. It's imperative that it's oriented thus: the pad back has a stubby pin at centre, that must seat between the spokes, and be well seated thus. This prevents the piston from rotating when the parking brake is applied. If the piston manages to jump the pin, rotate, it'll be providing constant pressure, dragging the brakes, and cause grossly bevelled wear, uneven rotor contact, hot-dog fingers, and possession. I'm kidding, those last two.

Anyway, do your brake job, silicon brake lube on the pins (use one that doesn't swell rubber. I'd mention an aftermarket brand, but someone will chastise me. It has the initials SG.) Put sparing amount of anti-seize on the points of contact between pad backs, shims, caliper piston and the two caliper "fingers" that grip the outside pad. Apply anti-seize to the smaller of any two components that'll be making contact; that way you get it precisely where needed.

Then reassemble all (torque spec in attached), and finally depress the brake pedal multiple times. This gets the pads well seated, and prevents the car detecting excess brake pedal travel. Do NOT apply the parking brake.

Lower the car back down. Reinstall the negative 12 volt cable. Still do not apply parking brake.

Go for a short test drive. Don't be rough on the brakes, just use them gently, as much as possible. Return home, and then apply/release the parking brake multiple times.

Then raise the rear again, and try spinning the wheels. They won't be friction free, due to slightl disk brake drag, but they should easily go 2~3 revolutions with a push. If so, you're out of the woods. Spin should be like this:

 

Just keep the key fob at least 20 feet away from the car. And do NOT open the drivers door!
If you are REALLY nervous, just disconnect the 12v battery ground cable.
Release the parking brake.

I did mine a few months back, they are as easy as the fronts, almost. Except for having to rotate
the puck/piston back in. Keep an eye on the dust boot as the puck spins so it doesn't bind.

 

With what's at stake, I like the car comatose.

 

Sounds like taking fob battery out is not an option, takes seconds to do that

 

AFAIK, the fobs could be in another State or Province, and if you have a momentary lapse and open the driver's door (say to pump the brake pedal), you'll be in a world of hurt.

You guys feel free to sail close to the wind; I've heard to many sad luck stories about popped out pistons.

 

Hard to open the door while working on the rear calipers.
You could put a note on the door over the handle that says DON'T OPEN!!!!!
If you're paranoid...

 

When I was working at rear brakes I did both methods, disconnect 12V battery and don't disconnect it (but keep driver door closed and key fob away).
Both methods works like a charm for me.

 

Can you explain your selection of Wagner pads? I'm ready for a brake job and am considering using more aggressive brake pads to help keep rust off the rotors. I now only drive about 7000 miles per year and rust initiates at the outer edge of the rotor and progresses inward. Pads are still good at 85K miles and calipers are free, but rotors are shot. I've seen some ads for ceramic/semi-metallic blends.

 

"...am considering using more aggressive brake pads to help keep rust off the rotors."

Not the best plan: more aggressive pads will just wear down your rotors more quickly, and keeping the rotors rust free is easy; just lightly apply the brakes when reversing. Voila! Clean rotors. Besides, a bit of rust on the area of the rotors is NOT important; any rust will be immediately removed when applying the brakes (meaning application beyond just regen braking). On a Prius, rotors wear down very slowly, unless the driver is crazy hard on the brakes.

I also drive less than 7000 miles per annum.

 

What about when you’re about to brake to a full stop at an intersection, shift to neutral then apply brakes until the full
Stop. Shift back to drive and accelerate?

 

I've never done any braking tricks, still the rotors look uniform.