Gen 3, 2003 Hydraulic Brake Booster HBB - Failure and Fix!

nckwltn

Explorer
If you have a Gen3, I'm pretty confident that unless the motor has been replaced, this is a problem that could pop up at any moment for you. I've got 166k miles on my 03.

Summary:
Hydraulic Brake Boosters commonly fail on Gen 3s. It's likely the motor, but could be the accumulator. You can find similar HBB systems on several model's of Toyota in junk yards. Grab the motor and motor mounting bracket, and swap them onto your HBB system. MUCH cheaper, but the motor will probably fail again due to similar wear.


Detailed:
Last Saturday morning, my wife was on the way to a meeting when all of a sudden the car started making a constant beep and the ABS and traction control lights came up. Thankfully she was only a couple of minutes away so she drove home. I gave it a couple of looks and didn't know what exactly it was. So I sent her off in my car and I hit the Google.

What I discovered was that my Hydraulic Brake Booster had just failed and my wife was probably only a few miles away from brake failure! A common problem on Gen 3s and other vehicles that use this type of system.

The hydraulic brake booster is electrically operated and not vacuum operated. From what I understand there is a pressure vessel (called an accumulator) that holds pressure built up by the motor. This prevents the motor from running non-stop. So when the motor stops working, you have a little pressure built up to make a few stops, but not too many.

I called the dealer, and they wanted $1,800 for the entire assembly. I also found a part number online and the dealer wanted $600 for the motor alone. Both items can be had from online for less, but it's still REALLY pricey.

I was thinking that it was quite strange that Mitsu would use a part that ONLY existed on this generation of Montero. A few google searches later I found several other Toyota models that also use the same looking part. Toyota's are much more common at my pick-a-part spots. Also, because this is a common problem on the Montero, I've seen that the HBB is usually the first thing to get pulled from a junked car.

A few online searches and I found a possible 2002 4 Runner that had a similar looking HBB system. Bought the motor for 30 bucks, put it on my HBB system.... bolted it all back up and it's working like a champ.



Short video showing the motor and hydraulic booster system. The problem is that the commutator bars are totally worn down by the brushes. Brushes don't have tons of life left in them either. The 4Runner motor that I pulled showed significant wear as well. Will be looking to pick up another motor on one of my pick-a-parts trips to have as a backup, and to see if they are all in a similar condition. Montero and 4Runner motors both were filled with that rust colored dust.



Nice detailed post about replacing the HBB unit: https://www2.pajeroclub.com.au/forum/showthread.php?t=46516

Part number for the motor only: MN102843

List of possible alternate vehicles to get the motor and/or HBB from. The electrical/computer connectors look to be identical. Only the brake fluid level sensor connector looks to be in different locations. Do you own research on this. I can say that I pulled my motor from an 02 4Runner. Don't know if all option levels of 4 runners in that year will even be equipped with HBB systems.

  • 98-00 LEXUS GS300 GS400 GS430
  • 01-05 lexus gs300 gs430
  • 08-10 hummer h3 h3t
  • 03-04 4Runner or lexus gx470
  • 02-05 Lexus sc430
  • 03-07 Land cruiser/lx470
  • 98-07 land cruiser
  • 07-09 Camry


How I identified other possible makes/models for similar HBB systems: https://www.google.com/search?q=lex...hWHgVQKHVsDAn4Q_AUIBygC#imgrc=WrGIbFWbC7aN8M: I went through the images and looked at the pages and what vehicles the parts claimed to be for.

You can see that with the motor armature removed how much of the brushes are left. You can also see the rust colored dust that was all over the inside of the motor. Possibly acting like an abrasive.
IMG_20170121_140251.jpg


Better shot of the dust
IMG_20170121_140255.jpg


You can see the missing sections of the commutator. 12 sections, 4 were completely missing, 2 were partially missing. If the motor came to rest with a brush over one of those missing bars, the motor would likely no restart. You can kind of also see that the commutator is also quite worn down by the brushes.
IMG_20170121_140310.jpg


If you pick a motor from a different make/model of vehicle, be sure to grab the rear motor mount. You can see that the motor I picked was longer than the original. The silver mounting plate is not connected to the original housing in this photo.
IMG_20170122_165418.jpg


This seems to be a common problem on all vehicles that use this type of braking system. We are just now getting to a point where the vehicles have enough life in them that the motors are failing. If you have a Gen3, probably worth taking a look at your motor and/or replacing it preventatively. If you were out on the trail and it failed, you're in big trouble.

I don't think it's possible to remove the motor without removing the entire HBB assembly for left hand drive cars. Can probably do it on right hand drive. That's because the motor is backing up against the left side of the engine bay. In RHD the motor will be to the open engine bay. This means you have to disconnect brake lines, pull the HBB unit and upon re-install bleed the brakes.

You're supposed to have a MUT2 scan tool to bleed the brakes, but I monitored the brake fluid level, and did a standard brake bleed, making sure to control the flow of fluid out of the brake lines so that I didn't drain the accumulator or the fluid reservoir too quickly and introduce air.
 

coffeegoat

Adventurer
This is a pretty killer find, this is a major issue and of all the fixes I've seen, I've never seen a cross vehicle fix. This might even mean the possibility of new aftermarket parts that can be subbed in.
 

nckwltn

Explorer
This is a pretty killer find, this is a major issue and of all the fixes I've seen, I've never seen a cross vehicle fix. This might even mean the possibility of new aftermarket parts that can be subbed in.
Unfortunately the Toyota HBB unit is virtually the same price.... Didn't check to see if Toyota sells the motor only. I'm sure they do. I came across a post where someones Land cruiser broke down and he had to replace the HBB unit.

The motor is poorly built for something so mission critical.


If nothing else, this discovery provides more possible donor vehicles.



From my reading there was a recall on the accumulator itself, so by this point the electric motor is certainly the weak point.
 

jdzl

Pontificator
Just did this, couldn't get the beeping and lights off until driving it about 1/2 mile after bleeding it. Now all good. Got a rebuilt unit off Ebay for $325 shipped including $50 core charge and 6 mo warranty. Way better than $1800 for a whole new HBB.

My motor looked just like yours, 145k on the clock for reference.

Cheers!
 

MrGalantguy

Mitsubishi Loyalist
My wifes 02 HBB failed last week. I bought another one and installed it. I am just having a issue bleeding the system. I have a brake bleeder kit that I have used many times with no issues but for some reason I just can't the system to bleed right. I haven't tried the traditional method as I don't have another person to pump the brakes but is there a special way to bleed this type of system?

I tried what the instructions said on the sticker on the HBB itself about pressing and depressing the brake pedeal 30-40 times but the pedal still goes to the floor. I proceeded to bleed the system with my bleeder kit I have used for years and the now I have some resistance on the pedal but if I keep pressure on the pedal after a few seconds it goes right to the floor. I didn't get a chance to rebleed the system as it got dark the the mosquitoes were tearing me up so I will try again later when I get home from work and just try to old traditional way.

I have no leaks in the brake lines or from the HBB either after inspection several times.
 
Last edited:

nckwltn

Explorer
I think I read something and remember something about having to pump the brake pedal 20+ times to get the accumulator charged up.... Then from there I think it's a standard brake bleeding job...

Sent from my LG-H932 using Tapatalk
 

MrGalantguy

Mitsubishi Loyalist
I think I read something and remember something about having to pump the brake pedal 20+ times to get the accumulator charged up.... Then from there I think it's a standard brake bleeding job...

Sent from my LG-H932 using Tapatalk
I tried that originally but didn't get any improvement on the pedal feel.
 

nckwltn

Explorer
I tried that originally but didn't get any improvement on the pedal feel.
Hmm.... I don't remember exactly what I did... but I had the entire booster out.... maybe more pumping on the pedal and keeping the reservoir topped off?

I do remember something about needing a special mitsu tool that plugs into the OBD2 and causes the system to cycle the motor.....


Did you pump with the car running or not running? might want to try both options.
 

MrGalantguy

Mitsubishi Loyalist
I read several different ways...some say with the key position on some saying off. I am going to bleed them the traditional way after work today and hope that works.
 

coffeegoat

Adventurer
When I did mine, I did the accumulator first, which requires leaving the key off and pressing the brake pedal like 40 times until it gets really stiff, and then turn the key on, the motor will turn on (you can hear it) and refill the accumulator. You repeat this process a bunch (5 times is) and then assume the accumulator is full. You can actually watch the brake reservoir go down and up as you empty and refill the accumulator. And then from there, go on and do all of the wheels normally until you have clear, bubble free brake fluid. This seemed to work fine as far as pedal feel and braking performance. However, I still get random, intermittent "anti-lock" warning lights. I've been meaning to figure out how to get the debug code, but it's so intermittent that i haven't gotten around to it yet.
 

MrGalantguy

Mitsubishi Loyalist
When I did mine, I did the accumulator first, which requires leaving the key off and pressing the brake pedal like 40 times until it gets really stiff, and then turn the key on, the motor will turn on (you can hear it) and refill the accumulator. You repeat this process a bunch (5 times is) and then assume the accumulator is full. You can actually watch the brake reservoir go down and up as you empty and refill the accumulator. And then from there, go on and do all of the wheels normally until you have clear, bubble free brake fluid. This seemed to work fine as far as pedal feel and braking performance. However, I still get random, intermittent "anti-lock" warning lights. I've been meaning to figure out how to get the debug code, but it's so intermittent that i haven't gotten around to it yet.
This is where I am concerned....I did this initially. Key on off position and pressed the brake pedal 30-40x's and the pedal never got stiff. My fluid level didn't even drop...stayed about the same. I tried this method a couple more times with only a slight increase in resistance of the pedal. I only got some noticeable change after I bled the system from the calipers in which the fluid level dropped a little and the pedal had even more resistance but still no where close to where it should be. Now when I press the brake pedal I get some resistance but after a few seconds pressing the pedal it goes to the floor again.
 

MrGalantguy

Mitsubishi Loyalist
Well good news...I was successful bleeding the system. It took awhile but I the Montero brakes properly again...I may have to go back and bleed the system one more time from the calipers but after 30 min of test driving everything works like it should. The buzzing sound and the ABS and Brake light eventually just went away after a few cycles of the HBB doing its thing and steadily the HBB just sorted things and pedal pressure became firmer as it cycled a few times. .

I actually followed the procedures from this Pajero owners site which not only provided info and tips on bleeding the system but actual repair /replacement of the HBB pump motor. This should be useful for any Gen 3 owner that encounters this issue.
Pajero HBB repair / bleeding procedure
 

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