Need Help in Diagnosing Abnormal Whirring of Brake Accumulator

Hate to say it, but I'm not sure that's actually possible now- not because of the nature of the brake problem, but rather because fuel prices are that low.

Our 2018 will never pay for itself vs. the nonhybrid cars we were considering. We got the prius anyway because it was nicer.

I've seen great brake system advice from @ChapmanF before, hopefully he'll see this notice and visit your thread. (you can also use that as a search key for some background reading)

Good luck!

 

After the air was allowed in, did you do the complete bleed process intended for replacement of the actuator?

 

The brake bleed utility in Techstream has two options, a short bleed for usual cases like you had a wheel cylinder off, and a long one for when the actuator has been replaced. It will step you through doing both rears, both fronts, both fronts again a different way (there are two separate sets of hydraulic passages that have to be bled with the actuator valves set different ways), and empty and refill the accumulator about six times.

It can take long enough to do that you should make sure the 12 volt battery is very well charged before you begin, and/or connect a 12 volt supply to it for support. But the idea is to end up getting the actuator cleared of air.

If air gets sucked in part-way through, my inclination would be to start over.

 

I would go for the second option, avoids the need to rush, and who knows, you might need to do it over? A charger's good to have on hand too.

 

I'm not sure a 'charger' there will do much more than slightly prolong your working time: if you have a charger that you have chosen appropriately to use with a Prius, it probably has an output of 5 amps or less, and that's lower than what the car will be consuming during the brake bleed. Of course it is better than nothing and won't hurt. I would still begin with the battery as juiced up as I can arrange, anyway.

At a dealership, they would hook up one of these, which is capable of fully supplying the operation of the car (at least without all the headlights, defrosters, blowers and such ... let's be reasonable), so nothing is being drawn from the battery.

 

You have a Gen 3? The stroke simulator is attached to the actuator. Techstream will tell you when to bleed it as part of the actuator bleed sequence. Make sure the cowl is removed before you start so you can reach the bleeder.

 

I am having an extremely similar issue to this, would you say instead of whirring its having a hissing noise? the hissing noise like air escaping when depressing brake pedal but its much worse than it originally was before changing my calipers.

 

How did you go about bleeding the system after changing your calipers? If in any doubt, I would revisit that procedure before anything else.

 

I posted a whole thread about it, basically just sucked it out with a tube, not a joke. The brakes definitely still stop the car, I just don't know why this sound occurs.

 

Which calipers did you change?

What was the reason for changing them?

Was there any chance the reservoir got low while you sucked fluid out with the tube?

How do the brakes feel if you do something to trip the system into fail-safe mode (pulling some ABS fuses ought to do it)?

You can get a false sense of security from how the brakes feel when the actuator is in control, because it will always achieve target pressure even if there's air in the lines (though you might notice something like a hissing sound).

What you don't want is for the brakes to drop into fail-safe mode for some reason when you're not expecting it, and have that be the moment you learn whether there's too much air in the lines to stop the car with straight hydraulics.

 

I need to change out my brake boost/master cyl assy as well as the booster pump. I simply don't have the funds to buy techstream and the cable so I was hoping to do it manually if possible? I assume I would do the long bleed you noted above, any chance you would be able to provide manual instructions to do that task? Probably will take quite a bit of Dot3 but its cheaper than any other options. Thanks

 

You could try "Invalid Mode" but I would then get a shop that has a proper scanner to run the procedure the right way.

Invalid Mode:

1. Press parking brake
2. Power Button twice
3. Press brake pedal and go into Neutral
4. Press brake x8 in 5 secs
5. Press Park
6. Press brake x8 in 5 secs and release
7. Press brake pedal and go into Neutral
8. Press brake x8 in 5 secs
9. Press Park and note Blinking brake light
10. You are in invalid mode

Bleed rear brakes by holding pedal down
Bleed front brakes by pumping brakes
Power down to exit invalid mode

Consider using charger on 12v battery during procedure

 

I'm not aware of any reason to think there even is an equivalent 'manual' way to do that task. The air needs out of all the internal passages, including ones behind internal valves that are controlled by the Skid ECU in a procedure commanded by Techstream.

The 'invalid mode' procedure suggested by rj might get you braking enough to get the car to a shop that has Techstream and can do the proper job. It might be a good idea to make that trip to the shop during off-peak traffic times or on less-traveled back roads.

If you can scrounge an old Windows laptop somewhere, doing this yourself using Techstream might not cost you any more than you'd pay a shop to have it properly done.