The title says it all, I replaced my master cyl. the other night, bench bled it then totally re bled the entire system. The pedal gets nice and solid until I start the engine then it turns to mush. I'm leaning toward the booster but its not hissing or anything, correct me if I'm wrong but doesn't the rod push from the pedal strait through the booster and push the master??? Even with the brakes bled out and good pads / shoes etc. I still couldn't stop this thing if I had too. I jumped the brakes HARD and still cant lock a wheel, it does stop but I would think without ABS I should be able to lock a wheel!!! Any thoughts?? Id hate to replace the booster now and still have no pedal. The pedal engages at the halfway point then is very spongy the rest of the stroke, but with the engine off it gets rock solid!! Wouldn't the booster hiss like crazy if the diaphragm was bad?? How do these old boosters work anyway?

 

Rear brake adjustments? MC not completely bled? Rotors/drums beyond wear spec?
You bled the LSP/BV above the rear axle too, right?

 

The rear shoes are new, the front rotors and pads have about 20,000 miles on them but look good. I didnt know that I had to bleed the prop. valve... Even with the rear circuit out of whack if thats the case should I be able to lock a front wheel if needed??? The pedal just firmly compresses to the floor!

 

there is a line from the front right brake line to the valve. you can see the tee in the wheel well.
If there's air in there, the front's won't lock either.

 

yup the lspv can be a PITA to bleed. if your drivers front is locking up on gravel if you mash on them, then it is air in your lines over on the pass side/rear lines.
on another note i was in shepherdstown a while ago at the fish and wildlife services nctc campus for fisheries training. fun little town.

 

had the same thing going on. replaced master and no good. went to a junk yard pulled a brake booster for like 13 bucks slaped it in and im all good to go. i guess if your MC goes bad it can leak break fluid into the BB and destroys the stuff inside that makes a brake booster work.....

 

Ill look this evening for the LSPV bleeder and instructions... I know there is one because I had to move it when I installed the rear lift springs. This kind of makes sense since the brakes have been spongy really since I replaced the fluid in the system. The booster seems OK, The diaphragm felt good and doesn't hiss or seem like it is leaking at all and the master was not leaking at all either, I just figured it wasn't holding pressure and that's why the brakes were spongy that it was allowing the pressure to go back into the reservoir, the same thing that happened to the clutch on my MX5, not leaking or dripping just not holding pressure... Yeah Shepherdstown is a great little town, the NCTC facility is a nice place too!! This area is nice because you can head east and be in DC / Baltimore in an hour or go west / south and be in the mountains just as fast! I love it

 

i did not see that you adjusted the rear brakes . Even new Brakes need to be adjusted.

Does the emergency brake work . That should stall the vehicle trying to pull out if it doesn`t adjust the rear shoes . there should just be a slight drag on the drum.

If I missed any of this I am sorry!! Hope it does fix the problem

 

i had same prob in 2 different vehicles, ended up being that i didint get all the air, i bled like an entire quart and a half out of the system and its good now on both

 

Sounds to me like air in the system somewhere as stated earlier. Does NOT sound like a booster at all. If you eliminate a booster completely (like stopping without the engine running) you have a high, hard pedal. It won't stop well but the pedal won't sink. Its a hydraulic problem.
The brake booster amplifies your foot/pedal pressure applied to the master cyl. A failing booster will just keep the pedal feeling hard at all times.
To feel this yourself, try holding your truck on a hill with the engine off. You will have to push harder than normal. I bet the pedal sinks then and watch out that your don't run into anything.

 

you said lift springs... did you install a spacer for the prop valve bracket? otherwise you wont have rear brakes and ebrake may not work either.

 

Thanks for all the help.. I did install the bracket between the prop valve and axle... Im betting its air in the lines from the PV.... Im going to re-bleed it again tomorrow.. I did adjust the rear shoes when I put them on a few months back but will re check them tomorrow as well as the parking brake! Ill let you know what happens. I bet its air though, I used a friends massive vacuum bleeder and pulled fresh fluid through the system but didn't know about the LSPV bleeder! Ive since had the rear hubs out to replace the rear diff and wheel bearings and just swapped the master with a fresh rebuilt unit, I did pull a lot of fluid through the system when I installed the new master but there must be a lot of air still in the system! I thought the LSPV just had an affect on the rear drums not the front brakes as well!

 

It could be possible that somewhere on the connections you had apart . there is one or more that is tight enough to not to leak fluid but will suck air.

Seems strange but i have seen it a few times.

For what it`s worth on these Toyotas i have never bled more then the rear wheel cylinders and calipers unless replacing the Master Cylinder which I just bench bleed I also ended up with great brake pedal feel

 

This is whats above the rear axle right? I just bought a truck with a 3 inch body lift. Should this be raised in some way? I noticed when bleeding my brakes that a lot more fluid bleeds through the front brakes then when I am bleeding the rear brakes.

 

I have the exact same problem! I just got a second master cylinder thinking i had a bad one out of the box? Will put on this weekend.

I'm curious what people think of what I experience when bleeding the system. I get no build up of pressure when pumping the brakes (rather when the GF is pumping them). THen when she holds down the pedal, very small amounts of fluid come out. When I tried a vaccum bleed, I pulled air bubles and a pint of fluid and the air bubbles never stopped. This lead me to believe the rebuilt master cylinder is leaking. I've checked all over for leaks and found none.

 

I had a brand new MC that just wouldn't bleed. Took it in under warrenty, got a new one, and all is well now.

 

I get a similar issue. But my mc had been leaking into the brake booster. When I drive around the pedal its self will be hard and then ill hear a pop from near the booster and the pedal will instantly drop an inch before applying pressure again.