so

the 4runner again, im stumped about this one


no fluid leaks, booster vacuum leaked a lil but ive fixed it

original problem;
brake were unreliable, sometimes they worked, sometimes they couldnt bring the truck to a complete stop going downhill(maybe 10-15% grade)

leak between the booster and master cylinder(only when i bled the master cylinder
pressure in the pedal both when the truck was running and when it wasnt was seemingly random, when rapidly pumping the brake while engine idles it would idle down, as though i had removed the booster line, however its a gradual change but in maybe 12-15 pumps the engine would nearly die


now;

got a used booster/master and replaced yesterday, slightly different booster and master but def off a toyota truck from my era, bolted up just right, took some brake line bending to get everything right, the booster/master look to be in fantastic condition compared to the rusty rotten stuff i took off

hen the truck is off, i can get pressure by pumping the brake, f i hold it the pressure will stay until i let off, if i let off for say 1.5-3 sec the pedal goes to the floor again, when the truck is running, the pedal goes to the floor and there is very VERY slight braking while driving

system has been properly bled, no sign of leaks, no sound of leaking pressure

im stumped

help me please, im leaning towards the new master cyl being the problem here

but dammit, at the rate im going thru brake fluid removing parts and bleeding i kinda want to have a better idea before i pull the cylinder, but this is my gut feeling

i didnt measure gap in the master cyl(however thats done) bc the master/booster were bolted together when i received them

i need ideas, going wheeling in just a few weeks

agreed, sounds exactly like a leak.

Is your engine running alright?

yea engine runs just fine

a fluid leak you say?

i haven seen any fresh fluid on the ground or anywhere, do you suggest repeatedly pumpng the brakes while the egnine is running, first checking for a fluid level change then for the leak location?

try running a line out of the master into the reservoir on both the front and rear. I have had this issue before and this fixed it by pumping the brakes literally a few hundred times. did you bench bleed the master cylinder before you put it on?

no, i just bled it afterwards

so loop the fluid from the cyl back into the resevior?
what would that do other than recycle the fuid

lol, my poor bent to hell brake lines

air bubbles can get caught inside the master which make it impossible to bleed. ALWAYS bench bleed before you install a master cylinder its way easier than when its on the truck

i hear a 'wet squirting air' noise when my wife pumps the brakes, cant tell exactly where it coming from

Yeah, if you did not bench bleed it, it is going to be a BIATCH to bleed. They sell bleeding kits specifically for master cyinders. They are plastic fitting with air lines which loop back into your master cylinder.

will look for it at orielly right now, otherwise im just gonna get more clear rubber line like my ozarka bleed kit i made, lol

thanks for the tips yall

bled the master and the brakes again, seems to have no effect on my problem, when the engine is off, it seems to build pressure faster, however, the pressure dissipates just the same if i let off for a second without immediately pumping again

im getting kinda frustrated

how about, adjusting the push rod?

perhaps my rear brakes are not adjusted properly, i dunno

You are going to have to bleed many more times my friend. Many more.

the master?
or everything?

either way if all i have to do is pump the brakes a billion times im cool with that, it means i dont have to buy anything, lol

alright, so, pumping the brake when the engine is off, building pressure, like i outlined earlier, it was quiet out(house ac unit turned off) and upon the release of the pressure i heard a click from the d side rear brake

when pumping the brakes there is no click, but when i take my foot off the pedal it clicks, i have a feeling that the auto-adjust for that brake is the problem, or part of it
will check that tomorrow

The only reason that it is building pressure if because the engine cannot act on the diaphragm in the brake booster.

Take the master cylinder off, bench bleed it. Attach your brake lines, and then start at the right rear, left rear, right front, left front. Just gotta buy brake fluid. Oh and try to buy brake fluid in a metal can as opposed to a plastic can. The plastic is porous and can sweat and cause moisture to build up in the brake fluid.

i think you are under estimating the bench bleeding process. you literally pump it until no more bubbles come out. make sure you never run low on brakefluid when you bleed or reattach the brake lines to the master

i did it already(no bubbles, perhaps what im actually underestimating is how much pumping is required to fully bench bleed the master, i went pick up a master cylinder bleed kit yesterday, had the wife help me, ill do it again(and for longer) today regardless

james, i was talking about the pressure when the engine is off, just like a normal car when the engine is off, like all 3 autos i own, but there is a distinct 'click' from the rear brake and then the pedal goes to the floor again

i apperciate yallz patience here, ive never had to work on a brake system like this before, i usually dont learn how to work on something til it needs workin on. hence why i can change a timing belt,open up a solid axle, all kinds of other stuff with ease, and have so much trouble with brake master/booster, lol

yeah brakes are a pain in the ass trust me

got the master out, on a table, level, have pumped it 150 times so far, lots of tiny tiny bubbles swirling around the resevoir, those little bubles will make this big of a difference in the performance of the master?

gonna pump it 150 more times using my big phillips driver, then install it and bleed the wheels again
trying to be done before the sun makes it to the driveway, i have about an hour left

You got this D....I have faith in you!

alright, 350 pumps bench bleeding, the pedal is as hard as it should be, however the pressure release still happens with the click in my rear d side brake, now i have to open up the drum and adjust the brake and i should be good to go

turns out the used master i had is no good, the original still works though

so i had a bad bosoter and a good master(thought they were both bad)

got a combo used booster/master for a total of $70, turns out the new booster was good and the old master was good, havent bled the brakes again yet, wating for my wife to get home, but when i bench bled the old master it was so much harder to pump than the 'new' one, it was effortless pmping the 'new' one, whereas the old one felt like it was actually pumping

Way to build up those fore-arms!

i have won the battle, the brakes work, the truck stops.... EVERYTIME

not just sometimes

how exciting! i can stop myself on the trails now instead of crashing into trees

just did a high speed test(20-30mph is extreme speed for this thing, lol)
it dosent stop on a dome, but thats only cuz 1 drum works and only 5 of 8 piston calipers work, but dammit it'l stop on a beach towel