Spongy brake pedal apears to be leaking fluid from brake booster

Try bleeding out the fluid. How to Bleed Your Brakes dummies

I guess either the brake pedal linkage is maladjusted or perhaps not fully returning so the master cylinder fluid inlet is remaining closed. In that condition when the brake fluid expands as it grows warm under normal use it cannot escape back into the reservoir and so the brakes are applied until the system cools down.

You can check this quite simply - when next the brakes are applied momentarily release one or two brake bleed *******. If that frees the brakes it will be time to take a close look at the pedal linkage.

The condition also sometimes occurs after the replacement of the brake booster and/or brake master cylinder by folk throwing new parts at the car instead of fitting them..
There must be a clearance between the brake booster pushrod and the master cylinder piston and in the absence of service tools , careful and precise measurements must be made.

I once had a car where the brake booster failed due to fluid leaking from the master cylinder and the brakes would auto apply and not release on that car.

if you can see brake fluid around the booster then yes it is most definitely not right, but sometimes these can fail without any fluid noticable, the visible fluid could mean that the brake master cylinder is failing & this will have an adverse affect on the booster power & performance, check your brake master cylinder first as this is a much simpler & easier repair than the brake booster & can be done at home on a flat drive or or street even, a Haynes manual is invaluable for the home mechanic & i recommend you get one as soon as you can as this will help you diagnose the problems with your vehicle before going to a mechanic/garage, if it is the brake booster at fault then i suggest you go to your local scrapper/breakers yard armed with tools & the Haynes/Chilton's Manual (Depending on which side of the pond you are from) & remove the brake booster from a now deceased Toyota 4Runner & remove the brake booster & master cylinder in one should only cost you a few Quid or Bucks & replace the part once your vehicle is back at home, once the parts have been replaced the brake system will need to be bled so that there is no air in the brake lines, this can be easily done with two people at home, Jack up one corner, remove that wheel & then just crack off the bleed nipple of the brake line Putting a bit of clear hose over the nipple to catch the excess brake fluid in a jug etc & have a friend push down slowly on the pedal, when only fluid comes out with no air then the system is bled for that wheel, Check the level in the brake master cylinder & repeat the process for the other 3 corners/wheels Once done your brake pedal should fell firm & Not spongy, If you get a spongy feeling when braking after this then there is still air in the brake lines & the system needs to be bled again, of course if you have done it right then your brakes should feel firm underfoot. Please don't forget to rate me, regards, Paul.

air in the line or bad booster. try getting the brakes bled if it doesnt fix it probably a bad booster

You may have a bad booster, but when your brake pedal goes all the way down, you have no fluid, a bad master or really bad calipers

check the power brake booster for a vacuum leak.
if good air can be in the brake fluid lines

sounds like your brake air booster is gone you must replace with remanufactured or new one! when booster fails pedel tends to get very hard to press !

If the brake lines and fluid is clear then you may have to look at the brake booster found at the other end of the brake pedal under the hood...

Hi there. If you have determined that the brake system doesnt have any leaks in the lines or at the calipers or brake cylinders, I would start by checking for vaccum to the brake booster first. There should be a large vaccum hose going from the power booster down to the top back of the engine. If this got unhooked or broken, your brakes will feel like old manual brakes rather than power. Make sure you have good suction by unhooking one end of this line with the engine running and place your hand over it to see if it has suction. GT would be the sporty version of the car and usualy has an emblem either on the fender or rear bumper saying GT. If you dont see this you probably have the L series.

if the booster is bad the pedal would be hard sounds like the e-brake is stuck take off the drums and make sure the arms are all the way back then did you adjust the rear brakes after changing the shoes