Thanks for your interest in helping NJ. It's killing me too! My pickup had a brake issue once that turned out to be the proportion valve not working right, but it still stopped. The shop that fixed it said they jacked up the truck and hit the brake and could still turn the rear wheels. I would think even with absolutely no rear brakes this thing should stop the front wheels. I had the 4Runner jacked up and had my wife hit the brake and I couldn't turn the rear wheels. So it seems everything works, just barely works.
When I do the booster pedal test in other cars, the pedal really drops, like up to 4 inches. In this 4Runner it's not dropping and I just can't figure it out! The booster has a lifetime warenty, so I can keep trying new ones but this is the 3rd one and it's a huge PITA to hook that thing up and re-bleed entire system each time.
I'm really trying to do everything I can before I have to call a tow truck and bring it to a shop.
If I can't figure it out soon, the things going to need a new windshield and tires!

 

Anybody with a similar vehicle, how much does your pedal drop when doing the booster pedal test?
When I pull the vacuum line off the booster there is a big hissing sound. So it's holding some vacuum I can't believe not enough to get it to stop.
Found this on MDMbrakeboosters.com FAQ

How much vacuum is needed to operate a booster properly?

For a power booster to function properly you will need at least 18" of vacuum. Anything lower will give you a hard pedal.

 

Im just throwing this out there, but doesn't the abs or something to do with the brakes attach to the power steering system on these trucks. I honestly don't know if this has to do with your problem, just throwing it out there.

 

Sounds like air in the MC, I know there are several threads on here explaining how to bleed it out because I wrote/added to them, basicly takes a syringe and rubber or cork stopper and pushing air out of the MC throught the resevoir inlets on the MC. Try searching and let me know if you don't find them.

I would bet a case of beer or two on this being your problem!

 

Hi , did you replace the calipers too? i worked on my dad's previa and the driver side caliper was stuck , it had pressure in the lines but somehow the rear brakes were the only ones working , check them out and rebuild them , it's 12 to 14 bucks per caliper ,Good luck!!

 

limon32, Could there be air in the master without having a spongy pedal, or without it going to the floor? The reason I'm leaning toward vacuum is because the system has been entirely bleed out 4 times and always having the same result and pedal feel. Plus, that booster pedal test.
FIRST94TOYOTAGREEN, I haven't rebuilt the calipers.
I'm starting to remember something here.
After the head gasket/valve job, one of the fuel injector o-rings was leaking and I had to pull the intake manifold again to fix it. I think this could have been the point where my idle got bad and brakes started to go. I still haven't had the chance to pick up a different vac. gauge...but the problem could be under there...
YellowTT, I couldn't find a depth micrometer anywhere to measure push rod clearance. I tried Play-Doh and did my best measuring. I'm aware this adjustment is very crucial, any ideas on how to get that measurement precise?

 

Hmm, my pedal felt pretty good and then would give out if that makes sense, when I had air in my MC, that was post MC replacement.

When I had the problem, I bled the brakes over and over only to have the same result. The problem was that the MC sits at such an angle that air in the MC would never get pushed all the way out, some would always stay stuck in the upturned end.

One sypmtom I never could explain was the brakes would bleed like normal for a bit and then fail to build pressure after a few pumps, so perhaps your problem is different if your not experiencing that.

 

I took off the MC one more time to double check the push rod clearance. It was a hair off but I fixed it and nothing changed. I'm pretty sure it's vacuum at this point since the new booster is failing the pedal test and I have that idle issue when it's warm.
I was thinking of getting a hand vacuum pump, giving the booster the correct amount of vacuum and see what kind of pedal I get with that.
From there I should know if it's vacuum or not. I've seen some stuff online to build a home made vacuum leak detector with some fittings from the hardware store, a couple pounds of air and soapy water...looks like this is what I'll try next. I'll post findings.
Thanks guys.

 

There was a large vacuum leak under the plenum and it ended up being a fuel injector! When I did the HG I sent off the injectors. Shortly after the rebuild there was a strong fuel odor and I pulled the plenum and found a leaking injector. I fixed that but apparently it ended up leaking on the other end.
This vacuum leak caused my idle issue and brakes issue.

Now from sitting for over a year, the new rotors I put on are pitted and have to be turned and the calipers are frozen...BUT the issue is fixed!

 

Congrats on finding it!