Avid reader but 1st time poster. Might i add that with the help of useful posts on this forum i was able to successfully tackle my timing belt and several other projects. I am in a bind this time though.
The brake pedal was kinda spongy since 4ever on my 207k mile solid truck so i decided to bleed the fluid. I pumped the pedal 20 times with ignition off to release all the pressure on the pedal. Then i bled the driver side brake with asst help. I noticed very little intermittent flow. So i decided to do the passenger side but i could not get any fluid out.

Next i decided to rebuild both calipers. I rebuilt the calz and reinstalled them and tried to rebleed. Absolutely no flow this time around on either side despite spending 15-20 minutes each side with asst help or with the vacuum pump.

There is no code or check lights. The brake pedal holds no pressure. The accumulator pumps runs for about 25 secs when ignition key is switched to on position. The reservoir level goes slightly lower when pedal is pressed but there is no fluid flowing at various (3 or 4) brake line joints that i tested on the driver side.

Needless to say i am at my wits end and need some help. I'd hate to shell out the money for a master cylinder unless i have to.
Desperate to hear your responses

No love???

As an update, i hear the pump running almost everytime i floor the pedal. 30+ Attempts with the vacuum pump and still no fluid.

Any suggested course of action?

Out of curiousity - Why did you pump the pedal 20+ times until there was no pedal pressure prior to the brake flushing and caliper rebuild?

I'm guessing that has something to do with it. I've replaced my calipers and bled my brakes several different times but never pumped all the pressure out prior to starting my work. Maybe @BlackWorksInc can chime in.

The idea is to pump the stored pressure out of the accumulator tank prior to servicing the braking system. It is technically in the FSM, but I've found its not entirely necessary unless you're trying to diagnose/look for issues in the MC/Accumulator section of the system.

That being said, you've got air in the system LOTS of air in the system, particularly in the master cylinder portion of the vehicle. The issue now is that you can't bleed that out by normal "pump & hold" technique as these hydraulically assisted units control each line individually and so you may not even be pushing fluid through the system beyond the solenoid pack. It is entirely possible that there is so much air in the system the vehicle can't won't physically open the solenoid pack valves to let fluid through because it thinks it has a fluid pressure issue (which should technically set a DTC in the Skid Control ECU as far as I am aware, but it is still a possibility.)

The only course of action right now is to have a Toyota capable scantool or the factory scantool perform a scantool driven bleeding procedure that actuates the ABS system to try and bleed all the air out of the system. Most likely they will have to do this about 3 or more times to ensure that all the air is purged from the system; this is of course assuming that the unit is still functioning correctly (which at this point I have little reason to doubt.)

Appreciate your input blackworks! Always learn something new from your posts.

Thanks a bunch BlackWorksInc. That likely seems to be the problem. Now to find the right shop for the job. Will report back.

UPDATE: The dealership tried to bleed the system for 3 hours but failed. In the end, they think it is the accumulator that's messing up. $930 + tax at the stealership.

What is the best way to tackle this? Is it DIY? What should I ask the tech. to conclusively diagnose that replacing the accumulator will solve the problem.

Looks like we can get one under $300. Quick advice sought...

Received another call from the dealership. After discussing with the "head chef" they conclude that there is no way of conclusively diagnosing the internals so the suggested prognosis is a new master cylinder ($3150). I was kind of expecting that...

Tech notes mention bleeding the brakes and the master cylinder but unable to get steady flow from front brakes. Rears bled fine (which I find unusual...)

Any ideas?

The rears can be bled conventionally if I remember correctly, the fronts need to be computer actuated (though these days with the TIS Scantool, it will do all of them because its easier, before the TIS we had to use a jump box.)

The reality is that there isn't any accurate way to diagnose these units, I've tried and tried; but I haven't found anything that's reliable enough to make me feel comfortable using diagnostic wise. At this point you're probably better off buying a MC than trying to rebuild it because we don't really know what component is actually bad...

You're going to want to get the part number from the dealership (should be on the P&A they gave you hopefully.)

Village Toyota seems to list 3 part numbers for the unit, which is a bit confusing; but you want to match it up because the ABS modules may be different from part number to part number. (its annoyingly confusing...)
$2030 BRAKE BOOSTER ASSY, W/MASTER CYLINDER. BRAKE MASTER CYLINDER (UZN21#) made by Toyota. #4705060081
$1849 BRAKE BOOSTER ASSY, W/MASTER CYLINDER. BRAKE MASTER CYLINDER (GRN21# made by Toyota. #4705035030

Or you can try calling/finding some reputable salvage yards who sell the unit. But again you need to make sure its coming out of an '03 (maybe '04) 4Runner 4.7L V8 (you did not mention if it is 4WD or not, but that matters as well) or have them match the part number, because you can have issues if you put a 4WD Skid Control ECU by accident in a 2WD vehicle.

After you get the part, installing it is straight forward; but it still needs the scantool to be bled properly. So you may want to just get the part cheaper from another source and then pay the dealer for labor and bleeding.

I think the front is conventional to bleed, rear fed by accumulator that provides steady state constant pressure, car on, car off, brake on, brake off.

I feel for you. I am waiting for the day mine goes. the brakes on 4th gen's is the worst thing. almost pointless to try to bleed these brakes at home. Toyota tool does it in 15 min. If you crack the rears and steady fluid fills the jar, I would say your accumulator is working. but that is just me.

So with the TIS scantool you can initiate a full automated bleed on each caliper?? This seems like a huge lifesaver. Do any other options like the bluetooth code reader with Torque Pro app accomplish this?

This confused me. I have replaced all 4 brake calipers and bled the brakes with no issue. My brakes work perfectly and I did not need to have any computer involved.

The only thing I kinda remember (been a year since did the rears) was I think I actually had to turn the car on between bleeding. I would turn the car on, let the mc develop pressure, turn it off and push hard to bleed the rears. Worked fine.

I just replaced the fronts about a month ago and I can promise those bleed as normal. Car off, pump up, push.....open valve. Close valve. Rinse repeat until no bubbles or air, and clean fluid coming through.

There isn't any need for a computer. I do hate these brake design though. I wonder how long until one of my remands sieze up. Oh well. Brakes are easy to do. Have not had any other issue.

As far as I know only the factory scantool and some more expensive ones that have Toyota equivalent ABS software will let you do this.

Most of the ones I have done end up getting a bubble or two in the unit and you just have to use the scantool. If you manage to not get air into the master cylinder assembly it can be bled normally.

I too have replaced the calipers and did the normal non Toyota bleed. I have seen on side failing from damaged or blocked or collapsed hoses. The rubber bits chunk off inside the line. On the outside the line can be cracked a soft in places but are actually a real mess inside. If the little chunk broke loose it can stop flow to the calipers.

Does anyone know of a scan tool you can buy that will do the brake bleeding procedure that is not the full blown TIS?