02 sport with 161,000 miles.

You know that sound that the brake booster makes when you start up your car? And you know how it usually ends after about 20 seconds or so? Mine is starting to make that noise at slow speed‘s while I’m driving.

And I’m not sure if it is related or not but as I’m coming to a stop sometimes the car lurches forward a little bit right before I stop. I posted about it a few months ago and was told it’s probably the ABS sensors, I just have not had time to diagnose that particular problem.

So before I was told to check the ABS sensors on that lurching problem, I grabbed the flashlight and did a pretty thorough examination of my brake booster. I could not find any signs of leaking, either in the engine bay, or inside the rig. No fluid on the carpet, no drips when I looked way up underneath, under the dash either.

Anyone else with this “super high-tech and super expensive” brake booster have it making sounds while driving?

When did you last flush the system? If the system contains few air bubbles the motor can run to build the pressure

My 01 will do it occasionally in stop n go traffic sometimes when I apply brakes rolling up to stop light.
211k mi with 11k mi on system flush n fill n bleed, shoes n pads.
Like mentioned flush system fill n bleed, there is a trick to bleeding this system follow FSM.
You can purchase another MC, you can buy parts from dealer to rebuild MC. Pump can be purchased aftermarket cheaper than dealer.

I was under the impression the 02 master cylinder unit could not be rebuilt, which is why used ones are in such demand. Please clarify.

No and No.

I've driven an '01 for about 195,000 miles so far, neither the brake booster or the abs booster make any sound at any time during start up or operating down the road. Yet both systems work as intended. Tells me something is wrong with your boosters, one or both. I'd get those checked out unless you can test per the FSM.

Luck and enjoy that runner.

So was I when I purchased a 01 24 months ago, since with research have found otherwise.
You can purchase complete unit, Toyota doesn't sell a rebuild kit you have to order by individual parts.
Two most expensive parts are accumulator and pump, pump can be reuilt not pump motor though, accumulator replacement only.
TOYOTA 4RUNNERVZN185L-GKPZKA - POWERTRAIN-CHASSIS - BRAKE MASTER CYLINDER | Japan Parts EU

Click part # copy 10 digit number, go to US Toyota parts site paste in search part for US price.
Still not cheap is better than going used that could chit the bed anytime.
Aftermarket pump/motor is out there for $3-$400 range.
Not as simple a fix as pre 01-02 is what it is.

Mine didn't start doing it till 205k mi, still very seldom and bugging the chit out of me.

Hope yall don't mind me jumping into the thread, but but I'm having the same problems as OP.

There is a very loud sound coming from the booster when I start up, sounds like a electrical motor (a pump I assume). It runs for a maybe 10 seconds then cuts outs. It runs intermittently as I'm driving, particularly often when I'm using the brakes a lot.

I did some googling when I first noticed it and "the internet consensus" (FWIW) said this was normal operation and not to be concerned. Example, here.

But I guess I should be concerned?

I have an 02 with 191k, just bought it and haven't put on more than 600 miles so far.

Edit: brakes feel great and no indications of any malfunction other than the sound.

2001 owner and mine intermittently makes that noise on startup and sometimes at stop lights since I bought the truck almost five years ago at 207K. Surpassed 250K and brakes still feel fine. This is normal operation from what I have been told from several people.

Brake ABS/Master cylinder assembly noise

@Jidaran the more the merry'er.
You and I have probably read same stuff, I have posted same here in last year since I've been digging into it.
I'm not concerned, I'm paying attention so I have my ducks in a row if/when chit happens.
Since this mornings posts example: Drove 25 mi, at house start up stop n go traffic stop lights dozen start n stop of engine doing errands.
Pump did not cycle one time, next time could be different.
@ToyotaBrah , good to hear what you said have fingers crossed.

From the owner's manual

"You may hear a small sound in the engine compartment after the engine is started or brake pedal is depressed repeatedly. This is a pump pulsating sound of the brake system, and it is not a malfunction."

I gotta say though, it's pretty ****ing loud. Not so loud that I'm convinced it's broken, but I'm surprised they'd engineer the system to be that loud in the first place. They tend to build these things to minimize noises coming from the engine bay (AC compressor, etc).

Edit: didn't realize this forum had automatic an automatic censor. Gotta keep it PG for all those 12 year olds wrenching on their trucks? Quick test: ******* shit ***** damn ****

Edit 2: so we can still use shit and damn. Good to know.

My Sons 01 does the same thing/noise. I’m not concerned, but I do have a complete other unit, just in case..


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FN = ****ing now days or really good wheels, some 12 yr olds I know talk some chit.

If I were to hazard a guess, it would be that the pump cycling is normal, but that it's fairly quiet when new, and that the noise progressively gets louder as the pump/bearings wear. Eventually as things wear further, the pump runs more often. I saw one video that sounded really terrible: YouTube

Knock on wood the 02 that I just bought isn't making any perceptible noise at this time (165k miles).

OP here...

So the fluid was a little amber in color, not too bad. Called a friend over and we bled the system and put in DOT 4 fluid.

But... we didn't bleed according to the FSM instructions, since I'm not very smart, didn't want to go searching for one online and figured I knew what I was doing (old school...rear to front) I did have the key in the "on" position though, so maybe a little-tiny bit smart?

Brakes seem a bit firmer now but that may be the placebo effect too.

Now that I've educated myself on how the FSM says to do it, and am much smarter for it ;) will I need to go back and do it all again? Like spend another $10 on DOT 4?

Will it make a noticeable difference?

Also, tell me if this is normal... The rears just shot out fluid all by itself. No pumping required. The pump went on, I applied the pedal and the fluid pumped out and when it turned from amber to clean, he closed it.

The fronts were more traditional.

Thanks for the help!