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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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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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. |
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. |
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 |
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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Pump assembly part #47070-60050 |
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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 ^^^^ https://i.imgur.com/PZ9Vqa8.png |
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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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