Brake actuator failing- how long to total failure?

There's a variety of ways a brake actuator can fail, so it's a little tricky to predict which failure you'll see (if any), much less a timeline for it, Some failure modes could involve only the loss of ABS, say, or the need to press the pedal much harder to stop.

If you have recently-developed barking, though, I would suggest using Techstream's long-form (for use after actuator replacement) bleed procedure, to see whether that improves the barking for a time.

I believe the barking to be the sound of some internal actuator valve being honked like a saxophone reed by the fluid rushing through it, and the rushing may suggest the presence of compressible gas together with the fluid. When applying the brakes, that requires more fluid to flow while compressing the gas bubbles until the target pressure is reached, and on releasing the brakes, extra fluid rushes back, driven by the re-expanding bubbles.

The failure mode that you would most like to avoid is the "floored pedal no stoppie" kind. That kind of failure doesn't seem very common, but there are some reports of it. I think the presence of compressible gas may be a factor. In a conventional brake system, you can't ever have much gas in the system without noticing, because the pedal would be mushy all the time, or, worst case, go to the floor without slowing the car.

The way Prius brakes work, though, some amount of gas in the system might not be too noticeable most of the time. The pressurized fluid from the accumulator just whooshes in as needed to reach the target pressure, even if that takes extra to compress some gas. The braking still feels pretty much normal.

However, if anything happens, any of the things, that can trigger the brake system to go to its fail-safe mode, then you could abruptly and unexpectedly find yourself with what amount to conventional brakes and bubbles in the fluid, and the result could be a floored pedal no stoppie.

 

I would suggest going through the long-form bleed procedure while doing all the things as Techstream instructs you to do them.

That means you should have a jug of DOT 3 brake fluid to start with, and wrenches and a little clear tube that fit the bleeder fittings. Make sure you have wrenches fitting both the front and rear bleeders; they might not take the same size.

I haven't done this procedure on a Gen 2. At one step, you might be told to open a bleeder under the hood somewhere, such as on the stroke simulator. On my Gen 3, that requires the windshield wipers and cowl out of the way (same procedure as for changing the spark plugs), which I deal with before starting the bleed procedure so as not to spend that time while the procedure is running.

I'm not sure how directly that translates to Gen 2, other than that you should make sure to locate all the bleeders you'll be instructed to open, and made sure you'll be ready to do that.

I made a couple earlier posts about the brake honk where I said clarinet reed, but I later decided it sounds to me more like a sax.

 

@ChapmanF in one of your past posts you've mentioned using a stethoscope to listen in for leaks.

Which section specifically are you listening for the leaks?

Nitrogen canister?
Billet steel brake like block?
Valve/solenoid block?

 

What is the "other hybrid" that you are driving?

When I post about stethoscope tricks, it is usually in a thread about a Gen 3 Prius (or c, or v), which has the brake system where the pump and accumulator are in one assembly and the master cylinder/booster/actuator are in another, and the stethoscope might save someone the expense of replacing the wrong thing.

But this is a thread in the Gen 2 forum, and in Gen 2 the actuator, pump, and accumulator are all in a single assembly, so there is less chance of picking the wrong thing to replace.

Well, I like how they sound, and I know the buzzy ones have reeds.

 

@ChapmanF in my case, 2014 Camry hybrid so similar to Gen 3.

On the accumulator, do you listen at the nitrogen canister or the pump motor?

On the master cylinder/actuator I assume you listen to the solenoid block?

 

So far, I personally haven't had to do it. But if you have an internal-leakage issue, and a goal of deciding which of two largish assemblies more likely contains the leak, and you've already paid for a mechanics' stethoscope, there is no additional charge per location that you touch with the stethoscope's tip, so you will probably let your curiosity guide you toward where you hear a flowing sound most clearly in between runs of the pump, and base your conclusions on that. (Keeping in mind also that metals and liquids both conduct sounds quite well.)

There was a recent thread in which a video was posted by a shop mechanic, showing replacement of a Gen 3 actuator, and the mechanic mentioned hearing the sound clearly with a stethoscope. There was also another recent thread where someone had an even shorter pump cycle (which could mean a larger leak) but was not able to localize a sound. (In that thread, it might be that the short cycling is a result of lost gas rather than leaking fluid.)

So it might be hard to give hard and fast rules. It is probably better to think in terms of what you are hoping to learn, and that your stethoscope is a listening device you can freely employ in that process.

 

Did you ever end up finding a good hybrid shop near Philly? Looking at an actuator repair on my '09 (110,000 miles). Still deciding what my plan is, but I'm new to the city and have yet to find a great mechanic.

 

just did my 05, it did this for 600 miles before showing codes, after showing codes it would sometime not stop in first reversing from start/park to reverse. there is always a mechanical connection from pedal to master cylinder, but the actuator/pump assembly can still fail in more than one way to make brakes not work or work less, easily causing an accident or worse. best not to drive until fixed. its really not that hard of a job. remove windshield wipers and cowl first, take less than 15 min with power ratchet. easiest bleed job ive done ever so far also... no scanner needed. i did it with orange plug pulled and 12v aux disconnected, standard pedal pump-bleed at calipers/wheel cylinders. took less than half a quart of dot 3 for whole system and bleed.

04-09 same for actuator/abs replacement part# 44510-47050

can get for $300-500 ebay or less at local wrecking yard... call them wrecking yard, they get offended if you say junk yard lol

mine failed due to removed brake reservoir cap and dirt in system...previous owner lost cap. clean fluid/brake fluid flush every 50k should make it last longer...

 

Hello. I have to replace on a 2004. I also have a 2006 and a 2010 (fleet!). I am finding conflicting reports about whether the actuator is the same for all Gen 2, 2004-2009. Some wrecking yards claim it is. Toyota parts site says it is not. And the part number listed above (44510-47050) does not come up at all as a valid part on the Toyota parts sites. I am seeing 4450047091 for 2004-2006, and 4450047141 for 2006-2009. Problem is I can't find a '04-'06 in any local wrecking yard. Can anyone speak authoritatively whether 4450047141, listed for 2006-2009, will work in a 2004? Thanks

 

I personally just replaced the ABS accumulator pump (aka ABS pump) and removed it from a parts car on offerup and part number was in fact 44510-47050. I was looking for a few weeks even on ebay and found actuators that were claimed to have been removed from early models (04,06) and had the same part number as the one I got from the 08. Could be that the part number was superseded, idk.