91 pickup ext cab 3.0 5 psd manual
work done
rear brakes including wheel cylinders
process taken;
replace parts, remove old fluid from reservoir with turkey baster. Replace new dot 4 non synthetic. Have the old lady pump old school to bleed. No air, fresh fluid at both rears

Symptoms;
brake pedal no pressure, will build up with no pedal drop, start truck no pedal pressure

Steps taken;
bleed more, truck running, not running. Have brakes at bottom of pedal, can pump with truck running get pressure, release pedal and wait a minute, no pressure
checked all work for leaks, pulled master from booster to check for fluid weep, pull vacuum line from booster, nice whoosh
wtf, lol
signed,
‘Baffled

 

I’m guessing master cylinder

 

Do you adjust rear brakes so they drag a bit on both sides? Bleed proportioning valve?

 

Yes,
there is no brake pressure, front or rear, front wasn’t touched

 

with cap off of MC look inside and have someone mash the brake. You should see a squirt of fluid come up. if no fluid comes up, the MC is bad or full of air. if full of air, you can just slightly mash brake slow about 1/2-1 inch or so. Do this many times and it might purge the air. If the MC is old, get a new Aisin MC for safety reasons.

Was the old fluid dark, almost black?

 

Fluid was black
hence the flushing out. I’ve ordered a master, resigned to replace.

 

Don't forget the alignment of the MC shaft to the pedal is critical. Make certain to align the brake pedal and the shaft going to the MC according to the book. It's very important to the functioning of the brakes, since it determines what port of the MC is used when the pedal is pushed.

Make sure you bleed the LPSV last. It's just as important as the brakes. A lot of people either don't bother bleeding out the LPSV, or don't even know it exists.
If it hasn't been used a great deal, ie: you've never had a heavy load in the rear, it wouldn't hurt at all to disconnect the bar from the axle to the LPSV, and flex the bar to fully actuate the LPSV a few times.
My mechanic put my 87 4Runner up on a lift a couple years ago, the wheels dangling down loose so we could run the truck to check for a noise I'd heard. IOW, the LPSV was actuated all the way down. When he dropped it off the lift again, put the weight back on the wheels, the difference in the brakes was like night and day.
I figure it was the actuation of the LPSV fully one way, then back to "normal", that did the trick. From now on, I am going to flex the LPSV fully both ways when I go to bleed the system every few years. THEN bleed the system. I figure that it can't hurt anything, and maybe even do some good.

Good luck!
Pat☺

 

lsvp was bleed last, master has not been removed. All was working well before rear brake replace

 

I just went through this a month ago. Replaced front rotors and pads and basically lost all brakes. Could get it to bleed after MANY pumps. barely any pedal feel. Could pump while driving to get pedal but it faded very fast. eventually lost all pedal and wife rear ended someone at low speed. Replaced the MC and it works perfectly again. My fluid was black too and even a flush didnt do anything. I suspect that while flushing and bleeding, a piece of debris went through the MC and wiped the seals.

 

That was my thinking as well, waiting on master

 

What is a great front caliper replacement. Got a rounded bleeder screw

 

get a set from rock auto.

 

napa had same ones, no shipping and easy core charge reclaim, about the same price
thanks

 

If the Master cylinder does not cure your problem.

Bad bleeder in one of the replaced wheel cylinders.

Poor connection drawing in Air but not leaking Fluid which can drive you crazy to find .

Then so many are not aware this can happen.

Good Luck

 

Thanks, issue resolved, was master

 

Glad it's squared away now!

Enjoy the truck
Pat☺