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Old 05-15-2023, 03:52 PM #1
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Brake Issue - Need Help

I need some help trying to decide where to start looking to rundown a brake issue.

2000 SR5 4X4 w/3.4L. 310K miles. I bought it used a couple of years ago.

In the last week I've started having an intermittent issue with the brakes. The brake pedal will be extremely stiff with very little braking occurring at first. It's more common at low speeds (read low engine RPM), but it's intermittent. Got plenty of brake fluid.

I replaced the brake pads and rotors about 35K miles ago. They've been trouble free until last week.

Where should I start looking?

Thanks!

Lefty
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Old 05-15-2023, 05:38 PM #2
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Sounds like brake booster going bad or perhaps check valve or vacuum hose. Do u hear any hissing noise when pressing on pedal? That's where I would look. Good luck

MikeM
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Old 05-15-2023, 06:23 PM #3
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Yup. At 23 years old some of the rubber items are beginning to breakdown, ie the rubber diaphragm in the vacuum brake booster.
I had the same intermittent loss of power assist brake. Until one day there was no power assist at all. A new booster fix my issue.

Part of a good power assist system is it to hold vacuum for a good part after shutting off the car. Before running the engine, with the engine off, you should have 1 or 2 brake peddle pushes with power assist until the stored vacuum in the booster runs out.

Obviously this apply only to the 2000 and earlier. 2001 and 02 uses a totally different and expensive braking power assist system.
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Old 05-17-2023, 09:46 AM #4
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So, the problem has become constant, which is super annoying.

I pulled the check valve yesterday. When I removed it, there was a vacuum inside the booster - that's after it sat in front of the office all day, so the booster is holding a vacuum, and the check valve appears to be working. Right?

What else should I look into?
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Old 05-17-2023, 10:57 AM #5
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Quote:
Originally Posted by lefty556 View Post
So, the problem has become constant, which is super annoying.

I pulled the check valve yesterday. When I removed it, there was a vacuum inside the booster - that's after it sat in front of the office all day, so the booster is holding a vacuum, and the check valve appears to be working. Right?

What else should I look into?
I'm running into this with my 1st gen as well. I do believe that it's still the booster that's failed regardless of it holding a vacuum. If the diaphragm has failed the vacuum will pull on the entire booster, not just the "front" side of the booster.

If you get in your 4Runner, don't turn it on yet, pump the brake a few times and hold the brake down (you don't have to kill it). While still holding the brake down, start the car: if the booster is working appropriately the brake pedal should sink down a little bit as the vacuum is drawn. If that doesn't happen, you're brake booster is not doing it's job.
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Old 05-17-2023, 01:32 PM #6
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If you don't have a u-pull nearby and you're skeptical about buying a new OEM booster, don't be afraid to order a used Ebay unit. I had brake issues on cold mornings that were not resolved with a new OEM check valve. A $100 OEM brake booster from Ebay (free shipping) solved my problem.

I'd rather run a used one than one from an auto parts store, but a brand new Toyota one was hard to justify. Good luck!
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Old 05-17-2023, 01:58 PM #7
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OP seems to be in rust free Texas, and less likely to happen.
Sometimes the caliper pistons will get stuck into the caliper bore and produce a hard pedal feel.

Junk inbetween the piston and caliper bore freezing the piston in the bore.
Or a ripped outer dust seal on the caliper pistons, letting in water to corrode the gap inbetween the piston and caliper bore.

As part of troubleshooting you need to rule out this is not happening in your situation with a good inspection.
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Old 05-17-2023, 03:16 PM #8
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Thank you everyone! I appreciate the input!

Lefty
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Old 05-17-2023, 05:52 PM #9
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Quote:
Originally Posted by lefty556 View Post
Thank you everyone! I appreciate the input!

Lefty
Let us know what you find!
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Old 06-02-2023, 02:53 PM #10
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It was the brake booster.
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Old 06-03-2023, 10:39 AM #11
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Thanks for posting back as it will help someone else down the road. Glad your fixed...

Sent from my SM-A536V using Tapatalk
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7 3rd gens listed in the build thread (2 are parts mobiles)
Build Thread: https://www.toyota-4runner.org/3rd-g...os-builds.html
Brillo's Bucket Fluid Ex changer: https://www.toyota-4runner.org/3rd-g...ml#post3358086
Sparks Plugs Wire and Coil Information: https://www.toyota-4runner.org/3rd-g...on-5vz-fe.html
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