Brake fluid leak

Check rear of Master Cylinder--If wet likely Master Cylinder Leaking and Booster Damaged. They Should be replaced as a mated pair. (for warranty) and brake lines removed and system bled.

Sounds like you have an air lock in your distribution block or it could be a bad distribution block all together. Sometimes you can tap it lightly and the air lock will bleed out. Also check your vacuum booster. If it is real hard to press the brake petal down, with the motor running, the vacuum booster diaphragm is blown, or there is a vacuum leak in the line to the booster. Pull the vacuum line off the booster with the engine running to see if there is vacuum to the booster, this will likely make the engine stall out if the booster is working properly. A little trick I do when bleeding my brakes is take about 16 inches of clear tubing that fits the bleeder, then get a quart Mason jar stick the tubing that is attached to the bleeder into the jar, then add about and inch of brake fluid to the jar and start pumping the petal. Always keep an eye on the jar and your master cylinder as to not let the master cylinder run out, or the jar to overflow. Hope this helps, good luck. If I think of something else I'll do another post.

This is a standard Vacuum operated brake booster.. If you are having fluid leaking at the rod that attaches the brake pedal to the booster it is a bad Master Cylinder. The Brake fluid will eventually destroy the diaphram in the booster if it hasn't already. . Replace or rebuild the Master Cylinder and wash the brake fluid out of the booster. When the booster goes bad the brake pedal will become very hard to push.. because you will have lost "boost" This is not really a hard job. If fluid id leaking somewhere else.it should be very easy to spot.. Brake fluid looks like oil leaking..

first check on every wheel make sure you see no wet . from brake cyclinders leaking. make sure brake fluid is full. when you replaced master cyc. did you bleed that before you hooked lines to it if not do that. abd bleed all brakes again. if still pedal goes down then it is the brake booster its self. hope this helps.

If there is no visible leaking at the wheels around the braking assembly's, then the fluid will be leaking out he back of the blake master cylinder into the vacuum booster. The master cylinder is where you have been topping up the brake fluid and the booster is the big black thing the master cylinder is bolted to. You need to have this looked at by a mechanic for proper repair (unless you really trust someone),as brakes are something I think are important to a vehicles operation.

Just as a note, there is no need to buy a new master cylinder, as most brake places would have exchange units available.

1of2 Master cyclender needs replaced or try bleeding your lines.

Not likely that the booster is an issue. The booster would not be able to overcome the brake fluid compression.
First open and inspect all brakes for leaks, adjustment, etc. Check all brake lines.
So if no leaks, did the fluid go low in the MC? If so, pad consumption would eat more than a MC reservoir of fluid, and not require MC replacement, but rebleeding and top up of fluid. If the pads are worn, and you replace them, often this will expel air back through the MC.

If you determine the MC is faulty, bench bleed the new one before install, or you will have lots of problems getting air out....

Sounds to me like a major vacuum leak if when you say the brakes are tight. Do you mean the pedal is real hard. If this is the case, Your power booser for your brakes are done by vacuum. If you know where your master cylinder is (where you put the brake fluid), the master cylinder is bolted to is the brake power booster. If you look at the picture below it will kind of look like that (the one in the picture is from a Nissan but looks the same). You can see in the picture on the top left of the unit is a inlet going in. That is where a major vacuum line goes. Check that line from the booster to where it attaches to the engine. Make sure it is connected and without holes and stuff in it. The reason I feel this may be your problem (and i may be way off) is that you say it accelerates by itself and sounds like it's gonna blow. To me the sound could be the air you hear leaking and the car accelerating by itself could be due to high idle because of a vacuum leak. the booster itself could be leaking as well as it has a diaphram in it that could break and cause a vacuum leak and you would hear it as well. I hope I am on the right path for you and can only go by what I am reading and that is what it sounds like to me. I hope this helped and good luck. Here is the picture:

Bad Master Cylinder and or Power Brake Booster would be the first things to check.. look for signs of a leak under the hood first, monitor brake performance!!

1. What is the Brake Fluid Level?
2. Are you losing any Brake fluid at all? Are there any puddles or noticeable wetness on the ground or on the tires/wheels? With vehicle parked, the reservoir filled (overfilled), and engine running: pump the brakes and check on the ground and back sides (inside portions) of the wheels. Look for any brake fluid leaks.
3. Leaks from Calipers usually means a leak from the caliper piston. The rubber seals will be wet.
Leaks from Drums usually means a leak from the wheel cylinder.
4. In any case of leaks from the wheels - replace the calliper OR wheel cylinder.
For caliper leaks: change the brake pads, and clean the rotors with brake cleaner.
For drum leaks: clean the drum and brake hardware with brake cleaner, and replace the shoes.
5. If no leak is detected from the wheel area's: check under the Master Cylinder for wetness indicating a possible leak.
6. If no leak can be found: you MAY have a rear seal leak in the Master Cylinder which is pumping Brake Fluid into the Brake Booster (that large disk looking thing attached to the fire wall, attached to the Master Cylinder in front).
a. Use a large drip/catch pan under the Van in the area on the Master Cylinder.
b. Disconnect the brake lines from the Master Cylinder using a flair wrench.
c. Remove the two nuts (12 or 13mm?) attaching the Master Cylinder to the Brake Booster. If you have been using a lot of fluid, and have found no leaks, here is a good possibilty that all that brake fluid has collected in the Booster; so when you detach the Master Cylinder from the Brake Booster, all that fluid will come rushing out!
7. If there is Brake Fluid inside the Brake Booster: there is no cleaning that out. Brake Fluid is very caustic to the seals inside the Booster and should be replaced.
8. Of course the Master Cylinder will also have to be replaced.
9. After replacing the Master Cylinder/Brake Booster - make sure you get all that spilled brake fluid off the engine compartment area parts! I use a brake cleaner, then mild soap and then water to rinse. Clean any Brake Fluid off Paint imediatley as it will quickly dissolves finishes and paint.
10. If no leak is detected and the Booster is clear, there may be problems with the Booster One-Way Valve. This is attached to the outside of the Booster and has a hose from an "advance" connected to it. This maybe malfunctioning where you are losing power. Replace this first before deciding to replace the whole booster (in cases of NON-LEAKS ONLY). If that did not work, there may be inner seals inside the Booster that have failed. That means a new Booster.
11. In any of the above cases: Make sure you bleed the Master Cylinder correctly and bleed the brakes (at each affected wheel) correctly. Any air in the brake lines will decrease your braking proficiency or could result in brake failure.

Let me know if this helped or if you have any additional information or questions. Feel free to contact me at FixYa.com!