What could cause this hissing sound when the brake pedal is pressed?

Hopefully the link works. I'm talking about the hissing sound, not the buzzing from the brake booster.

I had my brake actuator replaced by an independent shop a few months ago, using a used brake actuator I bought off of eBay. Could a faulty actuator or a bad installation cause this sound? I've noticed it since the replacement, I think. Might just be in my head, but I feel like stopping time has been increased too. The car will slow down, but going from maybe 15ish mph to 0 takes longer than I feel is normal, and I'll end up nearly flooring the brake pedal to make sure I stop in time.

I don't really know much about the brake booster system, but could the noise be some kind of leaking vacuum line? Is that a thing?

I've recently replaced the front brake pads, and more recently, I flushed my brake fluid.

 

That's what I had suspected... I do have a mini VCI cable, but I've never been able to correctly set up Techstream thus far. Every time I try, Techstream is missing functionalities like the "Utility" button and the check system health function.

But as indicated by my other thread, my water pump seems to have just gone out, so I guess I have a more important problem to deal with before this

 

Hmm sounds like I'll need to look that. I have a copy that says 12.something as well as a copy that says 13.something. Had the same missing functionalities issue with both.

I plan to more fully look into it after I solve my water pump issue. I foresee it taking time, as info about Techstream seems to be a mess, sort of all over the place

 

I did. Why?

 

I know this is an old thread, but I never ended up addressing this issue. I would like to do so soon. To reiterate the issue, there's a hissing or whooshing sound when I press the brake pedal, the brake booster buzzes and re-accumulates pressure quite often, and coming to a complete stop requires me to depress the pedal further than I would normal expect. Also, when I'm braking to a complete stop, once I get down to around 8-12mph there is sometimes a feeling of the car jerking forward. I believe I read that's about when the car shifts from regenerative braking to the mechanical/friction braking?

Some things I believe the issue may be: 1. Brakes or brake booster/ABS system need to be bled/flushed. 2. Brake booster ("booster assembly", pump/actuator assembly, or both) are bad. 3. Something else?

Before this, I had an issue with my brake booster and ended up replacing just the "brake booster assembly" and not the pump assembly. I replaced using a used part from eBay, but it was apparently the updated (or rather, superseding) part, as it was listed with "mark" #47210-47310, which is part #47050-47140. The actual part came did have 47210-47310 on it, so it did seem to be the newer version. The replacement was done by a local independent shop. I really don't know if the independent shop did the proper bleeding after replacing the brake booster assembly. I did want to try doing the bleed myself, but haven't been able to get Techstream running correctly yet. The last time I tried setting up Techstream, I was missing a lot of functionality, for example the "utility" button.

Some time after the brake booster assembly was replaced, I was working on the front brakes and accidentally had the front right caliper piston pop out. I put it back, but I was warned that there could be a leak in the piston boot now that the piston had come out once. However, I have not noticed any loss of brake fluid, so I doubt there is a leak there.

I did later do a brake flush, but that was my first time ever doing a flush or even a bleed, so I will be redoing it, as I may have done it incorrectly.

Any ideas?

Many online parts sections of Toyota dealerships in the southeastern region of the USA currently have a 25% off promo going on right now, up until midnight tonight I believe. It looks like I can get the brake booster accumulator and pump assembly at less than $900 total currently, so I'm tempted to just buy brand new brake booster parts to give myself peace of mind that my issue isn't with the brake booster parts. Maybe sell my current parts after to recoup some of the cost, as they still seem to be okay, no codes currently. Thoughts?

 

Apologies, I did get them mixed up.

I'm thinking of buying both. Like I had mentioned, when I previously had my brake booster issue (thread linked in my last post), I only replaced the "brake booster assembly" (not the pump), and the replacement was a used part from eBay, although like I said, it was the newer (superceding) part number. At the time, my specific codes had to do with the master cylinder and linear solenoid valve, if I'm remembering correctly.

Currently I don't have any codes. The issues I do have, as like I said in my previous post, are the whooshing sound, the brake booster tries to accumulate pressure/buzzes pretty often, and I end up having to press the brake pedal harder than expected once I get down to 8-12mph

 

Any chance someone can point towards a Techstream setup tutorial that worked for them? I'm currently poking around trying to set it up again, so that I can perform a bleed, but haven't had much luck with getting Techstream to work so far.

I have a 64-bit Windows 10 laptop, but will be running Techstream on a virtual machine. I currently have a 32-bit Windows 7 virtual box as well as a 64-bit Windows 11 virtual box installed.

 

Nevermind! Managed to get Techstream working properly for the first time ever! Will post more details later, but for now the version I got working was 12.00.127.

Gotta go get stuff ready to try a brake bleed!

 

So... I failed to bleed properly...

For some reason, all the vinyl tubing I have is the wrong size and won't fit over the front wheel bleeders or the stroke simulator bleeder. I had standard airline tubing, as well as some tubing that came in a cheap auto part store brake bleeding kit that I found to be worthless. I was able to get the tubing to fit over the rear bleeder nipples, but not the front bleeder nipples. Any suggestions on what size/what kind of tubing I'd need?

Also,the ECU kept disconnecting for some reason at the stroke simulator bleeding step. Any ideas why? Is the master reservoir level sensor supposed to be disconnected during the entire process? In the beginning it says to disconnect, but I haven't seen it say to reconnect yet, although like I said, I haven't gotten past the stroke simulator part.

Just adding that I was trying to do the bleeds using the one-man bleed method where you keep one end of the hose submerged in brake fluid in a container, keep the hose raised above the container and bleeder valve in the middle, and keep the other end connected to the bleeder valve.

I would have likely had better results with better fitting tubing, as well as if I had a partner. Will try.

 

No, I haven't been able to fix it yet, unfortunately...