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Old 08-21-2017, 07:31 PM #16
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Originally Posted by theoutbackdream View Post
Jesus.. Sounds costly... Maybe i'll go ahead and bleed the system again..

Just want to make sure i'm not dumb and the 4r doesn't require a special method of bleeding the brakes, as i've done the same pattern to many other cars without problems.. But we do start bleeding from the farthest from the Master cylinder, pump 3 times and hold, and open the bleeder valve. That should be it, like every car?

Is there a way to cycle the ABS system?

One interesting thought came into mind from another poster about an electric motor pressuring the accumulator.. @mar5168
Is there a way to cycle this and make sure it's pressurized completely while bleeding the system?
If you have a vacuum air bleeder adapter thing, you do not pump the brakes, you just connect the bleeder and let it do its thing until you can see clear brake fluid coming out, you repeat this process for every brake cylinder. In regards to the ABS activation, I believe I saw a techstream section under "live test" that would let you cycle the abs system.

https://www.amazon.com/dp/B016M68PUW?psc=1
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Old 08-22-2017, 02:35 AM #17
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Quote:
Originally Posted by duffdog View Post
If you have a vacuum air bleeder adapter thing, you do not pump the brakes, you just connect the bleeder and let it do its thing until you can see clear brake fluid coming out, you repeat this process for every brake cylinder. In regards to the ABS activation, I believe I saw a techstream section under "live test" that would let you cycle the abs system.

https://www.amazon.com/dp/B016M68PUW?psc=1
Yea I wish I had a air bleeder thing.. but just too costly. haha

Hmm.. I'll have to look into that... thanks!
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Old 08-22-2017, 06:14 AM #18
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im using the motive product fluid extractor, works fine for me, sometimes i think i should of went to harbor freight and got the air fluid extractor just like that amazon link, i think they only cost 20 or so.
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Old 08-22-2017, 04:21 PM #19
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Quote:
Originally Posted by theoutbackdream View Post
Jesus.. Sounds costly... Maybe i'll go ahead and bleed the system again..

Just want to make sure i'm not dumb and the 4r doesn't require a special method of bleeding the brakes, as i've done the same pattern to many other cars without problems.. But we do start bleeding from the farthest from the Master cylinder, pump 3 times and hold, and open the bleeder valve. That should be it, like every car?

Is there a way to cycle the ABS system?

One interesting thought came into mind from another poster about an electric motor pressuring the accumulator.. @mar5168
Is there a way to cycle this and make sure it's pressurized completely while bleeding the system?
As long as the key is not in the off position the accumulator will always be charged.

Sounds like you're air bound somewhere.

Here's what I would do:

1.) Take it for a drive and get the ABS to actuate. This can free up any air bound up in the system.

2.) Bleed the brakes again.

If you have access to techstream you can use it to bleed the rear brakes. It'll run the booster eliminating the whole pump, pump, loosen method.

Front brakes need to be bled as normal.
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Old 08-31-2017, 01:21 AM #20
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Quote:
Originally Posted by mar5168 View Post
As long as the key is not in the off position the accumulator will always be charged.

Sounds like you're air bound somewhere.

Here's what I would do:

1.) Take it for a drive and get the ABS to actuate. This can free up any air bound up in the system.

2.) Bleed the brakes again.

If you have access to techstream you can use it to bleed the rear brakes. It'll run the booster eliminating the whole pump, pump, loosen method.

Front brakes need to be bled as normal.
I took the car to some moguls and kept going at the moguls after a few times, the brakes got significantly tighter, and the more and more I did it, the much better the brake pedal felt, but would get closer to the floorboard. I probably did the moguls a total of 10 times. Went home and bled the brakes. It was just air coming out for a good while. After I bled the brakes, the brakes felt solid, consistent AND worked with little effort/pressure on the pedal. YESSSSS!!! Thank you!!!!
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Old 08-31-2017, 11:44 AM #21
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Quote:
Originally Posted by duffdog View Post
Its the ABS computer playing with the valves and reading sensor values for some strange subroutine. I still haven't figured out why its doing that. Mine does it too.
yes its the abs doing it but its because there is a blockage in the valves, usually caused by rust making the valves stick.

it will continue until you replace the abs system, sorry to be bearer of very bad news, but that is the only way to fix it

went through this with my tacoma and i even gambled and bought a used abs from salvage yard that worked for a month before it started doing it as well and then i bought a brand new unit to fix it permanently. the price wasnt as insane as the abs unit on a 4runner though.

and i went through "everything" before i found the problem, new brake hoses all around, new brakes rotors and drums all around, new master cylinder, new brake booster, new brake pedal linkages, finally brought it to toyota dealership and one old dude about to retire knew what it was and told me what i had to do to solve the problem. none of the young guys had a clue because a plug in computer couldnt tell them what part to replace lol.

Last edited by keakar; 08-31-2017 at 12:03 PM.
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Old 09-02-2017, 09:35 AM #22
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Quote:
Originally Posted by theoutbackdream View Post
I took the car to some moguls and kept going at the moguls after a few times, the brakes got significantly tighter, and the more and more I did it, the much better the brake pedal felt, but would get closer to the floorboard. I probably did the moguls a total of 10 times. Went home and bled the brakes. It was just air coming out for a good while. After I bled the brakes, the brakes felt solid, consistent AND worked with little effort/pressure on the pedal. YESSSSS!!! Thank you!!!!
Glad I could help!
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Old 07-10-2019, 12:56 PM #23
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Quote:
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Lots of bad information in this thread. Let me start by explaining how the hydraulic system works and my personal experience with poor braking in regards to my 2007 4wd sr5. This is not meant to step on the toes of previous posts, but should clear things up. I hope this can act as a reference for other members as theres a ton of assumptions as to how this system works, but not a whole lot of published information.

Here is a very brief explanation of how the hydraulic booster works: Brake assist force is created by pressurizing an accumulator (basically a small tank) with brake fluid. When you depress the brake pedal, pressurized brake fluid is released from the accumulator and helps with braking force. An outright failure of this system would result in a very firm brake pedal with very little travel. All the braking assist force lost would have to be supplemented by means of your leg.

My experience - About three months ago I noticed that my runners braking pressure and pedal travel became very inconsistent. There didn't seem to be any logic or correlation as to when the pedal feel would be ok or when it would require more force or the travel would increase. So I did the go-to first steps without any real diagnosis. I bled the brake system multiple times and activated abs on damp roads, but this didn't seem to help. I knew all of the calipers were fine as I replaced them all just less than a year ago.

I began researching how the hydraulic system works and decided to buy a m-vci cable and install techstream. Since there wasn't what I would consider a hardware issue from the brake lines at the hydraulic booster, down to the calipers, I assumed there must be something wrong with the hydraulic booster.

With techstream I began logging vehicle speed, master cylinder pressure sensor voltage, accumulator pressure, and brake pedal switch state. I logged this to and from work for a total of 3 hours and then parsed through the data. What I found surprised me, and taught me volumes about the system and logic used to control it.

The data showed the electric motor pressurizes the accumulator with brake fluid until the accumulator pressure sensor reaches 3.8 volts. When the accumulator pressure sensor dips below 3.2 volts the electric motor cycles again until the 3.8 volt conditional is reached. Therefore, we can deduce that any time the accumulator sensor voltage is between 3.2 - 3.8 volts we should have all the braking force the toyota engineers designed into the system. Additionally, if the voltage drops too low, as in the event an accumulator or booster motor failure, an alarm will sound indicating a brake system failure and a DTC will be set.

Well bummer, it appears everything is in range… hmmmm. Knowing that data doesn’t lie I had to revaluate my approach. During college, and for 3 years after, I worked as a technician for Honda. I began racking my brain trying to think of interesting braking cases. I distinctly could recall a pilot that came in complaining of inconsistent braking. I test drove the car and the right front wheel bearing was so loud it sounded like a helicopter. I racked the car and there was almost a quarter inch of play in the bearing. The advisor sold the wheel bearing citing it as a safety issue and told the customer the brake diagnosis would follow afterward. I certainly wasn’t going to be driving this vehicle until that bearing was replaced. So I replaced the bearing and much to my surprise the inconsistent braking issue was resolved. Play in the bearing allowed the pistons to be depressed and subsequently when braking more travel was required to push the pistons out of their bores.

Remembering this, I decided to check the wheel bearings and found the left front had failed. It had significant play in it. I replaced the wheel bearing an my braking issues were resolved.

Lessons learned or reinforced:
1.) A bad wheel bearing can manifest itself as a braking issue

2.) Wheel bearings can fail quietly. (I’ve replaced tons of wheel bearings and never have had a sealed unit bearing type fail quietly.)
Old thread, but wanted to say thanks for the legwork done and then posting this... I'd been putting off what I figured was a bad booster/accumulator for a while (like a year) because the pump would cycle a lot.

Within the last few weeks the brake pedal started getting really erratic, grabbing high, then low, sometimes it would fade or pull to the right. Needless to say, I was leaving a lot of room in front of me in traffic HA.

Searching for "inconsistent brake pedal" brought this thread up - thank goodness!
The RF wheel bearing had ~1/16 of play in it. Maybe the MT tires hid the noise, but I didn't hear anything. After replacing (both) wheel bearings the pedal is back to normal, not to mention steering is better.

I've only been driving it for a few days, but I don't think I've noticed the accumulator pump cycling like it used to either.

Thanks a ton @mar5168
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Old 07-16-2019, 06:55 PM #24
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Quote:
Originally Posted by gfxcruncher View Post
Old thread, but wanted to say thanks for the legwork done and then posting this... I'd been putting off what I figured was a bad booster/accumulator for a while (like a year) because the pump would cycle a lot.

Within the last few weeks the brake pedal started getting really erratic, grabbing high, then low, sometimes it would fade or pull to the right. Needless to say, I was leaving a lot of room in front of me in traffic HA.

Searching for "inconsistent brake pedal" brought this thread up - thank goodness!
The RF wheel bearing had ~1/16 of play in it. Maybe the MT tires hid the noise, but I didn't hear anything. After replacing (both) wheel bearings the pedal is back to normal, not to mention steering is better.

I've only been driving it for a few days, but I don't think I've noticed the accumulator pump cycling like it used to either.

Thanks a ton @mar5168
Super glad to hear this helped you out, and hopefully it's also helping others

Last edited by mar5168; 07-16-2019 at 06:57 PM.
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Old 11-24-2022, 06:49 AM #25
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This thread is pretty old but I thought I'd ask here while I'm building up rep. I have a very similar issue on a 99, where when I press the brake pedal, the bite point varies greatly. Sometimes its up high, and super touchy, and other times its much lower and similar to how my 2wd 4runner would always brake. I can consistently get it to bite high by letting it idle in park or drive, after driving for some period of time, and then driving again. It's almost like it has something to do with the vacuum, or the brake booster. It is repeatable.

The problem is that the car brakes fine, it is not abnormally stiff, and the pedal never drops to the floor. It just grabs high sometimes, and grabs at a lower, more normal level other times. The bearings have no perceptible play, the brake booster passes the hold down pedal and start the car test, and the master appears to be okay. Behind the master where it attaches to the booster is what looks like an old leak that dried and rusted, but the fluid level is normal.

Any ideas as to what this could be? I likely need all new wheel bearings with over 300k miles, but to do it right and get the tools necessary I would need to spend around 1k-1.5k. Spending that on wheel bearings when it was a master cylinder or booster all along would be a bummer. The brakes have been bled with the motive bleeder, so I think I'm safe there. Thank you.

Edit - Realized this is the 4th gen forum, but the issue is similar enough maybe it will translate to the 3rd gen. Thanks again.

Edit #2 - I found the solution. I had a remanufactured brake booster (grey not black) and the booster adjustment pin was pushed way too far forward. This kept the brakes slightly engaged and made them lock up after braking then idling. I readjusted and now the brakes work exactly like my other 4Runner. Hopefully the brakes aren’t ruined from the bad adjustment! Anyways, wanted to update in case anyone finds this thread and has a similar problem.

Last edited by Chrischrimbus; 12-11-2022 at 03:10 PM. Reason: Solution Found
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