Just changed brakes, now they are sticking. HELP!!!!

You might be able to raise the front of the car and try turning the wheels, see if you are feeling a strong brake drag ... then crack open a bleed screw, see if the caliper relaxes and lets the wheel turn more easily. That would reveal whether the caliper was actually being held clamped by fluid pressure from the actuator, or whether the problem was something more mechanical, perhaps at the caliper itself.

If the caliper relaxed with the bleed screw cracked, it would also be interesting to observe whether it relaxed with just one small spurt of fluid from the bleeder, or with a more prolonged flow out the bleeder, as if pressurized fluid from the accumulator was being steadily admitted.

There have been different schools of thought here about how to reposition the piston for new pads: the "just crank the C clamp and force the fluid back upstream because that always worked on granddad's car" school, and the "open the bleeder before cranking the clamp because you might not want to force brake line grot back upstream into the tiny actuator valves" school.

I was once in the first school, until I wound up with a dragging brake on my Gen 1. My problem actually turned out to be a bad caliper and I hadn't mucked up the actuator at all, but I wasn't sure until I proved that was what it was, so the experience put the fear of grot into me anyway, and now I am in the second school.

-Chap

 

Step #5 killed you!

NEVER, EVER push old brake fluid backwards thru the system, especially on vehicles equipped with an HCU (Prius), although it is a terrible idea on anything with ABS in general.

Reasons?
- Old brake fluid is corrosive as it contains moisture
- Old brake fluid contains small wear particles and rust
- All of the junk sinks to the lowest point in the system, the calipers!
- When you push the caliper pistons back, you are going against "Mother Nature", ie: Gravity
- Brake fluid has a finite service life, typically 3 years OR LESS, unless you live in the desert, then maybe 4 or 5 years at best

 

Just a few thoughts:

You only greased the lower caliper pins, didn't touch the uppers?

What grease did you use?

Has the brake fluid ever been changed?

 

I would not assume that it was (for you and me). I was only describing my situation. In mine, I had replaced an OEM Toyota caliper with a low-quality aftermarket reman, and that caliper had zero piston return. That story is here.

So in my case, by confirming the cheesy caliper was the problem, and replacing it with a decent one and having the problem go away, I was able to eliminate the worse possibility that I might have damaged the actuator.

But the problem I had has been diagnosed and resolved. Yours has not been yet, so it is too early to assume it is the same for you and me.

My earlier post suggested a test; if you can do that, it might tell us more than a lot of speculation.

-Chap

 

Right...

At this Time in Service and mileage, pin replacement is normal. Seems from the description like the HCU valve(s) are stuck partially open, causing some pressure to be applied to the calipers. Sure could be caliper piston seals are hardened and not pulling the pistons back when the brakes are released. Tough to tell over the internet.

 

I clean the exposed caliper piston with brake cleaner and a tooth brush very well before pushing back in. Getting crud inside the bore can cause sticking and/or torn seals.

Did you disconnect the 12v before beginning repairs? I've seen that recommended here.

 

He apparently didn't, says so in round about way in initial post. And yeah that could be an issue, I'm out of my depth though.

 

Did the new pads come with shims clipped to back of them? Sometimes those shims can be installed wrong and create kind of spring between the caliber/piston and the pad. That spring force will constantly push the pad to the rotor causing some brake drag.

All those valves are inside brake actuator assy. Sometimes it’s called ABS-control unit/module/pump.

It’s easy to check where the problem is but you should have techstream in case you get air in the system in some other part than front lines.
Check where the problem is:
-check that brake is currently dragging
-open the bleeder on dragging wheel
if it releases some fluid and immediately stops dragging then it’s hydraulic (or electric) fault
if it still drags it’s a bad caliber

PS. Toyota actually advises just to push the piston in without opening the bleeder valve. But then they also say to change the brake fluid every other year (at least here).

 

Here it's every 3 years or 48K kms if I recall correctly. It's for sure 3 years. This is since 2014 Prius year. Honda has always said tri-yearly, regardless of miles.

If you do this your brake fluid will be in good shape, and pushing the piston back without bleed screw open should not be a problem. That's the only way I've ever done it. With the Prius too, it should be in special mode whenever you start opening the bleed screws. See @NutzAboutBolts brake fluid replacement video, pinned in maintenance sub-forum.

 

Greasing the pins is the most important part. A stuck pin will catch the tire on fire really quick. It happened to me.

If you opened the door and it actuated the brake vac assist motor the piston will hyper extend. And also its not a good idea to push fluid back through the ABS unit.

This happens quite often. And usually requires a tow to the dealer. Opening a bleed screw will make the abs very unhappy also as it will see a loss of pressure. Going at the brakes without Techstream software is usually a disaster.

It does not take much at all to piss off the ABS unit. Its highly controlled and uses relay controlled solenoids for fluid metering. Pretty complex system. In fact at my Autoway dealer they refuse to even flush the brake system on G2 Prius. Apparently it cause the ABS unit to fail.
I asked for the flush they said no way. He said all the Autoways in there network no longer do flushes on this car.

 

That's a lot of worst case scenarios. I'm sure they are all possible, but I have changed the pads and rotors on both of our pruises without disconnecting the battery, and I pushed the caliper pistons back in without draining brake fluid. No warning lights or any other issues. Pretty sure I have opened the drivers door too and caliper pistons were not ejected. Just like any other car I have done brakes on, the brake pedal goes to the floor the first time till the pads move out to the rotor. The "brake computer" does not automatically preset the pads.
Brake fluid is not routinely changed where I live. I'm not sure the fluid has ever been changed on my 06 or 08. Brakes hydraulics mostly fail here because of corrosion of the pistons and hardware from road salt, not internal corrosion from old brake fluid. I also think you would have warning lights on if you had damaged the ABS system.

Since both sides are dragging I would suspect a problem with the way they were assembled. Are you sure you have the correct pads? Are they Toyota pads? I would start by taking them apart again and putting the old pads back in if you still have them. Are the flex lines in good condition? Is there a wear ridge on the rotors?

 

I once pointed a revolver at my face and pulled the trigger. It didn't fire, so it must be safe for everyone else to do also.........

 

You are doing yourself a HUGE disservice by working on the Prius w/o Techstream.

1) Buy mini VCI from Amazon. $20-$30. All the selllers are sellig the same knock-off cble and hacked Techstream software.
2) Get an obsolete Windows 32bit laptop (XP or 7). This will be your dedicated Toyota code reader. Many threads on install help for Win and Mac, just search.
3) Get a temporary subscription to Toyota TIS, the OFFICIAL service manual. $15 for a 2 day subscription.
4) Disconnecting 12V not specified in manual when replacing brakes. However, proper procedure to power down the system is required, which you may not have done.​

When you get Techstream up and running, double check your work, clean and lube the caliper slide pins, then flush the brake fluid. This might just resolve the issue, by forcing the appropriate valve open/closed, so the old fluid leaves the system. Assuming no physical damage to any brake realted component, the brake system/abs/related ecus will "relearn" the new status, and realize all is well. I base this on my experience, just barely moving moving the rear shoes when cleaning the rear brakes. Codes were rown and brakes were not working properly. Pnce the system was flushed, all was well.

READ post #1 from Galaxee. What services you need and what you don't | PriusChat. The Prius has a lot of brake fluid.

 

I'm not sure if it's different with second gen, but third gen, there are work arounds. Simplest, as long as you're not opening brake bleed bolts:

1. disconnect negative 12 volt lead at the outset, and when done, push brake pedal multiple times to firm up the pedal, then reconnect 12 volt.

2. For brake fluid replacement, set the car in "invalid mode".

I'd agree though, at this juncture, guess software intervention is needed. Maybe just run it by the dealership??