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Old 08-18-2023, 10:27 PM #1
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Lost Brakes While in Traffic

Howdy All,

Yesterday, as I was going back to work from lunch, I lost my brakes. Luckily, I was stopped at a red light - but all of a sudden, I started rolling forward into the intersection, and had to absolutely mash the brakes to keep from rolling forward. I was able to use the e-brake to get stopped and got a tow back home to figure things out. Before this happened, I didn't notice my brakes going bad.

For reference, it's a '99 Limited, 4wd, California spec, V6.

Symptoms:
-Hard brake pedal after depressing slightly with no resistance
-Hissing when pressing brakes until the pedal firms up
-No power brakes - but I can still stop the truck if I'm moving slowly, like when the truck is off.
-Probably others. If you have any tests to check for other symptoms let me know.

I read on here that some of you cold weather folks have had success by simply replacing the check valve... I was not so lucky. It was about 104 out when this happened, but I figured I'd start with the cheap/easy stuff. New check valve is in, no change. My hose going to the intake manifold is not cracked as far as I can tell.

I suspect the hissing when I press the brakes indicates there's a leak in my brake booster. Does anyone else have any ideas on a fix I can do without replacing the whole unit?

Here's a link to hear the hissing
3rd Gen 4Runner Brake Pedal Hiss - YouTube

If any of you guys have any suggestions on things I could try before spending a lot on a new brake booster, please let me know. Thanks!
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Old 08-18-2023, 11:28 PM #2
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Classic sign of brake booster going bad. Both mine and my buddies brake booster hissed and replacing brake booster solved the issue. Hard brake pedal is another sign of bad brake booster. Good luck

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Old 08-18-2023, 11:59 PM #3
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Been there did that. Same symptoms that you experienced. I though I was gonna wreck the 4r.

I had a backup used vac booster. All good after installing the backup.

Im guessing the rubber bellows in the booster just aged out. Surprising the booster lasted 19+ years.
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Old 08-19-2023, 12:38 AM #4
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+1 to the brake booster calls. The hissing youíre hearing is basically a vacuum leak within the booster.
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Old 08-19-2023, 02:14 AM #5
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Thanks everyone. Consensus online says to just replace the whole booster, but my wallet would prefer to rebuild it or change out the gaskets if that's an option. Has anyone done this before or have any experience in that?
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Old 08-19-2023, 10:38 PM #6
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Update. It was the brake booster. Got a good deal on one from the scrapyard and my brakes feel great. Thanks for your input everyone!
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Old 10-21-2023, 10:35 PM #7
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that is terrifying glad you're okay.
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