LOSING PRESSURE WHEN I PRESS BRAKE PEDAL, BUT NO OUTSIDE LEAKS

Your better off going by the feel of the pedal rather than measurements. Try this. With the engine off and the brake system cold remove the key from the ignition and pump the brake pedal. it should get progressively harder and your foot travels a shorter and shorter distance until its too hard to press.
Press and hold the brake pedal hard down then start the engine. You should feel the pedal soften, that's the vacuum inside the brake booster kicking in.
Release the pedal and again press it hard down, holding it there. The pedal should feel firm and not change. Release and repeat to make sure.
If the pedal has no resistance check your work as there is no pressure in the system. If the pedal is soft or spongey re-bleed the system starting with the calliper furthest away from the reservoir.

Brake booster has gone bad or u have a vacuum leak. Check the seals for leaks around booster where the. Fluid goes in the plastic holder. Check for vacuum leak going to break booster

It is very difficult to diagnose this problem with the little bit of information you gave. If the brakes are drum brakes check to see if the brake cylinder is working and has no leaks, lift the rubber seals and make sure there are no leaks there, check the brake adjuster make sure that works okay. If everything works and you bled the brakes properly, then the problem is most likely is the master cylinder or the wheel cylinder.



While bleeding the brakes always make sure you check the master cylinder reservoir to make sure the fluid level is up so you do not get air in the brake lines. When bleeding the brakes did you have someone press down hard on the brake pedal hold the pressure on the brake pedal when opening the bleeder then push the brake pedal to the floor keep it there, until you tightened the bleeder, then pump the brakes up and hold it there, while you repeated the bleeding operation by opening the bleeder when the brake pedal go\'s to the floor keep the pedal down until you tighten the bleeder and then pump the brake pedal back up then check the fluid level in the reservoir, keep doing it until the brake fluid shows no sign of air.



If the brake pedal is pumping up during the bleeding process and you made sure you got all the air out of the brakes and then the pedal go\'s to the floor, make sure the fluid level is correct in the reservoir and the bleeder is closed tight and there are no leaks in the lines, wheel cylinder, brake cylinder the brake adjuster is working and master cylinder, and if you still have no brakes then it must be a defective piston in the wheel or brake cylinder, if there is a seal problem with the pistons you will not get any pressure to push the brake fluid. let me know how you are doing.

Did you bleed the brakes properly? One person pumps the brake pedal then holds it down while another person loosens and then retightens the bleeder valve. This way no air can enter the brake line which can dramatically affect braking pressure and thus have no brakes at all.

Does the car have ABS ? And does it have an equalizer block for the 4 wheels ?
It sounds like the ABS has been affected, or there is an equalizer block that is stuck on the front wheels only.
Can you open the bleeder or the rear line on the master cyl and get fluid to come out by depressing the pedal ?

try to bleed the brake system start at passenger side then go to driver side make sure there is no air in the lines

if you talking brakes not clutch. you can pump the brakes all day long and they don't build pressure and you not losing fluids the master is out. now if you pump them up and they are rock hard your hydrabooster is out.now if your mechanically incline you can order a master cylinder rebuild kit for like 20-30 bucks which is basically orings from local parts store and only tools you need are snapring pliers. or you can change the master ,bench bleed it first then bleed out the rr,lr,rf,lf in that order.hope i help.all under 100 bucks

hello, your going to need a buddy in the truck pumping the brakes while you bleed them. With that first you need to verify that the master cylinder is full, if it is you can get started, there are two ways you can do this, the first is called a non-pressure bleed, this is when you break the bleeder loose and have your assistant push down on the brake pedal and when it is all the way to the floor you tighten the bleeder up before they release the break pedal. The second method is the pressure bleed. this one is a little bit more messy, you will have your assistant pump the brake pedal several times and hold firmly while you break the bleeder loose, the pressure will force the fluid and air out quickly. you will have to bleed both wheels untill there are no more bubbles in the fluid coming out. be sure to keep checking the master cylinder to verify that the brake fluid is full.

U are going to need a new brake master cylinder, the internal seals are leaking and allowing the fluid pressure to leak down, this why the sinking pedal

There is no shortcut in brake bleeding. Keep master full, start at rr, then lr, rf then lf wheel. You may need to go around twice. Don't mash down on pedal..easy pressure only and make sure you close the bleeder before releasing pedal each time. Unless the master has failed or there is a leak somewhere, you should have brakes when you are finished. If part of the master ran dry before you fixed the problem, you may want to begin bleeding at the portion of the master that was dry. If there is no bleeder there, just break line loose (push pedal down and close line back up)