Brakes are a whistling.. booster?

Ok so I've got some serious whistling coming from my brakes. It's only on the driver's side, not a rock in the rotor or anything. Probably the electro booster or something.

It's a loud whistle only at the very beginning of pushing the pedal. Once fully pushed it goes away. It also happens intermittently, during extra use, and not every time I brake. Super loud though. I have a TRD OR 4x4, so I have the electronic hydraulic booster, not the typical vacuum booster that many here have.

No fluid in the cab by the pedal. Can't see any leaks. Going to check the hoses this afternoon but figured I'd post for input. Any ideas?

Thx

video:
https://youtube.com/shorts/sEXcKO-aVHk?feature=share

 

When did you service your brakes last?

 

Have you pulled the tires and physically looked at all 8 pads, 4 rotor sides, and 2 drums? The wear indicators scream when worn. Look for gouge lines. Booster usually doesn’t make a sound.

 

I've heard the whistling can be from the booster... Soo idk.

I changed my rotors and pads within the last 6-8 months.. it's 100% a noise in the front left. I know that much. Outside rotor edge looks fine, no noticeable lines. Could be the inside, but I think it's coming from the brake master/booster

 

If it is whistling it is probably from the booster or the associated vacuum line.

 

check ALL lines

might be the booster

if its whistling use spray windex/glass plus bottle

some one sitting in drivers seat

someone listening at idle pushing brake pedal

spray lines + booster might indicate where the leak is

 

Does the engine idle rough when the brake pedal is pushed and the noise happens?

 

Well I’m probably wrong. The booster is driven by a vacuum so yes you could be right.

 

This is what I’d do. That is if you can reproduce the noise not rolling. The short amount of time since you last did the brakes, they shouldn’t be worn enough to hit the pad wear indicators.

 

The OP indicates that he has a TRD OR and as such likely has the electro-hydraulic version of the brake booster verses the more traditional vacuum assist type. The electro-hydraulic type has a high pressure pump driven accumulator and master cylinder solenoid(s) with an integral ECU.

This type of booster can make all kinds of noise, especially during repeated braking and other failure creating rapid pressure depletion in the accumulator, pump problems and I suspect internal leaks can also make noises. On mine, sometimes I get a high-pitch motor-like whine that can go on for considerable time.

I have been chasing a possible failure code on my '14. I ordered a complete new unit but have not had the opportunity to swap it out yet.
OP, mine has never triggered a CEL but I do get a periodic code displayed for low pressure in the accumulator when viewed using the techstream.

You may also want to dig around in the 4Runner forums as I believe there have been a number of failures on earlier generations that use the same type of setup for stability control and ATRAC operations.

 

Nope.. checked for that also.

Haven't heard the sound unless I'm moving. But I'll try hitting the brake repeatedly in the driveway tomorrow n try to reproduce it. Still troubleshooting

 

I'll check on that tomorrow. I've also read the leaks can be in the booster, so checking hoses with soapy water doesn't work.

I have a video of the whistle. I'll upload.

 

If you only hear the noise while moving then it's probably coming from down at the wheels

 

Right.. but it also doesn't happen all the time, either. If there was a rock or something (started while offroading) stuck I'd hear it every time I press the brake. Instead, it only starts whistling when I'm using the brakes a lot, almost like it can't keep up. IDK. It's weird as hell. Let me upload the video now.

Video of noise, turn it up
https://youtube.com/shorts/sEXcKO-aVHk?feature=share

 

Sounds like pads squeaking. Pads sometimes have a plate attached by rivets or clips to the backside. Maybe one broke loose or slipped out of position. Id look through the wheel holes to see the outer pad. Turn the steering wheel like turning left, maybe you can see the inner one, might need to turn right and look at it from behind. Easiest to just get it up on jack stands, pull that wheel off, get a good look at those pads. Take em out if necessary. You could try to recreate the sound. Once up on jack stands, spin the wheel by hand, have someone very gently apply brakes.

Then again, I could be wrong.

What brand pads and rotors did you use?

 

sounds like your booster diaphragm is leaking
its hard to tell from the video, is the hissing continuous while on the pedal?

 

Yeah, I do my own brakes. It doesn't sound like pads squeaking I've ever heard. I checked the clips, rivets, and shims visually, and everything seems fine. I'm going to pull the wheel off tonight and take the pads out to double-check, I just needed to go get more grease for reinstalling everything. It's stock rotors and power stop pads.

So I have the 2011 TRD OR, and it looks like it's electronically boosted and I don't have the big round rubber booster that others do. Or I'm confused. And the hissing is only sometimes, very intermittent, and when I push more than a tiny bit the sounds completely goes away. It's only the first 15-20% of pedal push.


And yes, yes I know. It needs a good cleaning under here. I offroad often, in Vegas, in a lot of dust.

 

You are right. I do not have a typical booster. It's an electro-assist system. See my image in the post above. I don't have a CEL or anything.

 

That really does sound like pad squeal either due to a worn pad or debris in the pad.

 

I don't see wear on the rotor, but could be on the inside. And if it was something stuck in there wouldn't it happen every time I hit the brakes? Either way I'm checking right now.

I pumped the brakes probably 30+ times in my driveway and never got it to make the noise. Which means it only happens while I'm moving so hopefully it's just something stuck in the wheel