Originally Posted by Hawaiian Hillbilly

Ok first off......THANK YOU TO THIS FORUM! Once again after searching through this forum I found a few threads and subsequent links to help me decide what was my next step in diagnosing my wifes 03 v8 4x4 4runner booster pump failure.

Symptoms: FLAT ASS BRAKE PEDAL! has brakes but very evident the booster was not functioning. I needed to stand on the pedal to get the car stopped. No sound coming from booster pump when ignition is turned on.

While searching for parts I quickly found out how EXPENSIVE this piece was! GEEEEESH! Dealer wants near 3500 bucks for a replacement......you can get used pumps and masters off of ebay from $800-$1500 and up! So needless to say I was not a happy Hawaiian hillbilly! However, I did find some good points in this forum which allowed me to tear down my master assembly and narrow it down to the accumulator and booster pump.

So, I took it all apart and focused on the booster pump itself since the problem was either the booster wasn't getting power or the booster was fried. I first tested the circuit to be sure the pump was getting power. At that point I was fairly certain that the problem was the pump itself. So I separated the pump from the accumulator. Then ripped into the pump itself and found that one of the 2 brushes which transfer power to the pump armature was stuck in the off position. Thankfully this hillbilly also owns r.c. cars and was somewhat familiar with how these things operate. I first removed the stuck brush and filed the rubbish off of the brush that was accumulating over the vehicles 271,000 miles. It was pretty gunky in the motor. Then cleaned out the motor replaced the newly "refurbished" brush and spring....and VIOLA! Tested the pump and I had rotation!

Reinstalled everything in its original places on the master and then mounted everything back into the car....followed the procedures (found in this forum) for bleeding the pump and accumulator (key off depress brake pedal 20-30 times then 10 solid pumps and turn ignition on listen for pump to operate) then continue to bleed each caliper normally. I sincerely hope this post will help someone out there save some hard earned cash!!

Here are some pics that I took throughout the journey. This Hawaiian Hillbilly needs my fireball and dissarono on all repair jobs....WOOOOO! 70% FIREBALL and 30% DISSARONO for those who may want refreshment specifics...aloha, HH

Originally Posted by earthrealm

good info here,
the pump in my truck comes on every 7 to 10secs, if my foot is on the brakes, so i think the pump assy may be working overtime, as it gets super hot after driving for a while.
this makes me believe the pump may soon fail.

am concerned to what is making it actuate that often, is it a leak or air in the system?, brakes work ok.

nb: this is a used mc assy i installed in the truck narch 2015, after the original crapped out

Originally Posted by BlackWorksInc

Very good write-up and I'm glad that everything worked out for you. Seems like the motors end up popping off on these systems more than anything, so for those who aren't feint of heart it's a worthwhile solution.

If you ever find a rebuild kit for these please update the thread with part numbers, I haven't seen anything last I checked; but I'm just one guy. Supposedly some member said he rebuilt these things but he/she never provided any further information, so I suspect they were a "click-bait" spammer.

Originally Posted by AuSeeker

Thanks Hawiian Hillbilly for this topic, very valuable for those who wish to attempt to repair what is a very expensive part to have to buy!!

I have read several times on the forum where BlackWorkInc has stated that he hasn't been able to find a overhaul kit so I'm also bumping this topic to add that there is indeed a overhaul kit for the actual master cylinder portion of this assembly and I know new OEM motors can be found on eBay for aorund $500+/-, as far as the rest of the componets I haven't found any source for them, but it seems the motor and then the actual master cylinder O rings going bad seem to be the most common failures of this assembly.

Here the part number for the master cylinder overhaul kit...

CYLINDER KIT, BRAKE MASTER, Toyota Part No.: 04493-60350

A link to the kit, you can also find this kit for a few dollars less doing a search, but the average price is very similar on most all sites I've checked.

04493-60350 - Genuine Toyota CYLINDER KIT, BRAKE MASTER

Originally Posted by earthrealm

how easy is it to change this oring ??, you have any tips or instructional video?.
i changed the accumulator on my truck, and issue still remains, so the leak is probablly from somewhere else, the o-ring perhaps???

Originally Posted by Hawaiian Hillbilly

I was so glad to see that it was an easy fix gang! Now the wifes 'new to us" 03 T4R V8 will be on the road today after I get the front axles and calipers changed out. Will post pics of that as well. Shes diving to the right when I hit the brakes now so I'm assuming front calipers are frozen or about to be....hate these things on our runners. Ive read a few threads in here about the 5th gen or fj caliper upgrades but was wondering what the part numbers are on those. Especially with the differing rotor diameters on our 4th gens. Someone please inform....mahalos all! HH

Originally Posted by earthrealm

@AuSeeker , my issue is this : the system is not holding pressure under sustained braking, especially in stop and go traffic, i believe it has a leak, somewhere, thus the pump cant keep up with re-presurring the system under sustained brake usage, some others said they resolved the problem after changing the accumulator and o-ring, mine wasnt resolved, though it got slightly better.

if i keep my foot on the brake pedal continously for about 5mins, the system will fail..and the alarm will start buzzing, i take off my foot from the brakes and idle for a min or 2, the pump will then repressurize the system, and the buzzing will stop and everything will be ok again.

Originally Posted by AuSeeker

When you replaced the accumulator and O-ring, did you put any oil/brake fluid/lubricate on the new O-ring?

If not then it's possible the new O-ring got pinched or cut and is not sealing well enough, but since it seems that you're only losing pressure while the pedal is depressed this might not be the issue, do you get the same issue if you just hold the brake pedal down and not pressing it repeatedly?

Other than that I don't know enough of how the booster assists the master cylinder, i.e. you have the electric motor that powers the booster pump that builds up pressure in the accumulator, how that pressure assists your foot pressure in the master cylinder I don't know, it sounds like you have a leak somewhere after the accumulator where it's assisting the master cylinder, I would think there's another O-ring/s or gasket at where the pressure assists the master cylinder when you depress the brake pedal, hopefully @BlackWorksInc will see this and hopefully has some input.

Originally Posted by earthrealm

YES i get the same result, if i depress the brake pedal continously in excess of 3minutes, the system would not cope, and the buzzer will come on, with all the lights, if i also engage the brake pedal intermittently, in serious stop and go traffic, same issue.

my theory is that i have a leak somewhere, if it was the accumulator, i believe brake fluid may be seen leaking from the accumulator. so i believe its an internal leak, so am suspecting the o-rings in the assy as highlighted in your earlier post, but i dont know where exactly that assy is located, and i dont have another unit to tinker with