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Old 11-04-2020, 06:20 PM #1
Matthew_H Matthew_H is offline
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2007 brake booster cycling a lot - some sort of vacuum leak?

So I recently noticed a hissing sound while I was driving. High pitched, almost inaudible inside the car while the engine is running. As it turns out, it's appears to be coming from the brake booster in the engine compartment. After it charges, you can hear a quite noticeable hiss that decreases in intensity until the the boost charges again.

The way I understand it, the brake booster should engage when the ignition turns on, and then again with every other press of the brake pedal (or whenever the boost needs a recharge). Mine activates with the key, takes several seconds to charge, and then re-engages after only being off for a few seconds. And it always engages with each press of the pedal.

I have an audio file of the behavior with the engine off and no pedal presses, but I don't know the best or preferred method of uploading it (either here or some other site). I'll look into that. In the mean time, any thoughts or suggestions?

Edit: I should note that aside from the booster running a lot and the hissing sound, the brakes work and I've never had a problem stopping.
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Old 11-04-2020, 06:32 PM #2
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Quote:
Originally Posted by Matthew_H View Post
So I recently noticed a hissing sound while I was driving. High pitched, almost inaudible inside the car while the engine is running. As it turns out, it's appears to be coming from the brake booster in the engine compartment. After it charges, you can hear a quite noticeable hiss that decreases in intensity until the the boost charges again.

The way I understand it, the brake booster should engage when the ignition turns on, and then again with every other press of the brake pedal (or whenever the boost needs a recharge). Mine activates with the key, takes several seconds to charge, and then re-engages after only being off for a few seconds. And it always engages with each press of the pedal.

I have an audio file of the behavior with the engine off and no pedal presses, but I don't know the best or preferred method of uploading it (either here or some other site). I'll look into that. In the mean time, any thoughts or suggestions?

Edit: I should note that aside from the booster running a lot and the hissing sound, the brakes work and I've never had a problem stopping.
That sounds like an accumulator leak to me. Can you tell if the hissing noise is coming from the silver canister, or any of its accompanying lines, on the left side of the master cylinder assembly?

If it is an accumulator leak, a dealer or mechanic will probably charge a butt load to replace it, so I recommend doing it yourself if you can

https://www.toyota-4runner.org/3560752-post10.html
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Old 11-04-2020, 06:39 PM #3
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Quote:
Originally Posted by Matthew_H View Post
So I recently noticed a hissing sound while I was driving. High pitched, almost inaudible inside the car while the engine is running. As it turns out, it's appears to be coming from the brake booster in the engine compartment. After it charges, you can hear a quite noticeable hiss that decreases in intensity until the the boost charges again.

The way I understand it, the brake booster should engage when the ignition turns on, and then again with every other press of the brake pedal (or whenever the boost needs a recharge). Mine activates with the key, takes several seconds to charge, and then re-engages after only being off for a few seconds. And it always engages with each press of the pedal.

I have an audio file of the behavior with the engine off and no pedal presses, but I don't know the best or preferred method of uploading it (either here or some other site). I'll look into that. In the mean time, any thoughts or suggestions?

Edit: I should note that aside from the booster running a lot and the hissing sound, the brakes work and I've never had a problem stopping.

More than likely it's the accumulator that going bad or at the very least the accumulator O-ring is bad.

The little electric ABS/booster motor runs the ABS/booster pump, the pump builds up pressure in the accumulator that pressure assists the master cylinder when braking and also is the pressure used when the ABS is activated.
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Old 11-04-2020, 06:57 PM #4
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same thing happened with my 2007 sr5 v6 in 2013 w/111k miles.. dealer wanted a lot of dough. ended up with a low mileage booster from a salvage operation.

believe the part was about $150, labor about $500-$600. no problems at 215k miles in 2020.
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Old 11-04-2020, 07:23 PM #5
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Thanks for the responses so far. Not excited about potentially needing to replace it, but I can definitely save cost doing the work myself (I've handled worse). Is it worth trying to seal the leak, or just replacing?

The hissing does sound like it's coming from below and to the left, but it's kinda hard to pinpoint exactly. I just took a quick video to illustrate what I mean, but the hissing doesn't come across very well.

2007 4Runner Brake Accumulator Hissing? - Album on Imgur
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Old 11-04-2020, 07:45 PM #6
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If you want to try to pinpoint the hissing you can do this. If you have a mechanics stethoscope you can take the probe off of it and just use the open end of the hose, or if you don't have one, just get a length of hose, like 3/8" hose and run the open end of it around the area where the noise is coming from, with either the stethoscope or the other end of the hose in your ears. When you get close to the noise you'll definitely know it.
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Old 11-04-2020, 08:25 PM #7
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Quote:
Originally Posted by Matthew_H View Post
Thanks for the responses so far. Not excited about potentially needing to replace it, but I can definitely save cost doing the work myself (I've handled worse). Is it worth trying to seal the leak, or just replacing?

The hissing does sound like it's coming from below and to the left, but it's kinda hard to pinpoint exactly. I just took a quick video to illustrate what I mean, but the hissing doesn't come across very well.

2007 4Runner Brake Accumulator Hissing? - Album on Imgur
I just had the stealership replaced my abs motor, accumulator and pump a couple months ago. Mine sound like that for awhile then it started screeching. I replaced the motor myself but it wasn't holding pressure because the new motor still cycles on and off. The part alone for all three was like $700 comes with pump, motor and accumulator.

Pump assembly part #47070-60050
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Old 11-05-2020, 12:30 AM #8
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Quote:
Originally Posted by Matthew_H View Post
Thanks for the responses so far. Not excited about potentially needing to replace it, but I can definitely save cost doing the work myself (I've handled worse). Is it worth trying to seal the leak, or just replacing?

The hissing does sound like it's coming from below and to the left, but it's kinda hard to pinpoint exactly. I just took a quick video to illustrate what I mean, but the hissing doesn't come across very well.

2007 4Runner Brake Accumulator Hissing? - Album on Imgur
Really, the only two parts of the master cylinder assembly that go bad are the pump and the accumulator. Personally, I'd say if you can happen to find where it's leaking from, why not give sealing it a shot and see if you can save some money - what's the worst that can happen

The repair manual says the rear brake lines can see up to 1,800 psi at full pressure, so I'd assume the accumulator must store at least that, if not more - so if you seal it, make sure it's a strong one
^^^^ If that is incorrect, please let me know ^^^^

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Old 06-16-2021, 12:48 PM #9
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Quote:
Originally Posted by Matthew_H View Post
Thanks for the responses so far. Not excited about potentially needing to replace it, but I can definitely save cost doing the work myself (I've handled worse). Is it worth trying to seal the leak, or just replacing?

The hissing does sound like it's coming from below and to the left, but it's kinda hard to pinpoint exactly. I just took a quick video to illustrate what I mean, but the hissing doesn't come across very well.

2007 4Runner Brake Accumulator Hissing? - Album on Imgur
Hi Matthew, did you ever find a solution to this? Mine is making the same noise. Considering trying to replace the o-ring or the whole accumulator.
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Old 06-18-2021, 04:10 AM #10
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Hi Matthew, did you ever find a solution to this? Mine is making the same noise. Considering trying to replace the o-ring or the whole accumulator.
I had this same problem on my 2003 4runner, I think the accumulator was not holding pressure so the motor kept running off and on. I got on ebay and bouth the accumulator, pump and motor assembly for 350 bucks. Installed it myself and now works like it should. Motor only comes on if you apply the brakes for a long period. once pressure is built and you do not use the brake it should never turn on. I got the rebuilt motor with the used accumulator from ebay.
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Old 06-18-2021, 07:07 AM #11
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Quote:
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I had this same problem on my 2003 4runner, I think the accumulator was not holding pressure so the motor kept running off and on. I got on ebay and bouth the accumulator, pump and motor assembly for 350 bucks. Installed it myself and now works like it should. Motor only comes on if you apply the brakes for a long period. once pressure is built and you do not use the brake it should never turn on. I got the rebuilt motor with the used accumulator from ebay.
Can you post the eBay link to the assembly you bought?
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Old 06-18-2021, 06:07 PM #12
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Quote:
Originally Posted by boulder View Post
I had this same problem on my 2003 4runner, I think the accumulator was not holding pressure so the motor kept running off and on. I got on ebay and bouth the accumulator, pump and motor assembly for 350 bucks. Installed it myself and now works like it should. Motor only comes on if you apply the brakes for a long period. once pressure is built and you do not use the brake it should never turn on. I got the rebuilt motor with the used accumulator from ebay.
did the same thing, but my reman'd unit was bad. sent it back no problem. hoping the new one will fix the problem.
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Old 07-26-2021, 01:29 AM #13
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3 culprits are

bad pump motor
bad piston oring
leaking accumulator.

the first 2 are the common failure points, and a relatively easy swap/ fix if you have the spares
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