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Discussion Starter #1
Hello everyone

I am in a tough bind here. I just got screwd by a friend that sold me this up van. Any way, yesterday I was out with my 4 kids and all of the sudden , NO BRAKES! Pedal go's to the floor but if you pump it you can get the van to stop. I have looked all over and no leaks at all. I replaced the master cylinder and still no brakes. Just keeps fading to the floor. When I press the brake it makes a air leak sound from the back under the van??? I'm lost here, I have a air leak sound that goes away after 2-3 pumps from a system that is not leaking anywhere, Clean fluid all around after the replacement of the master. I believe the sound might be coming from this piece in the back that I think is a proportioning valve. I think. The sound is being incredibly hard to pin point. I have even tried using a stethoscope on the lines to try and narrow it down.
Please help with some thoughts as soon as possible. I start a new job next week and there is no way me and my wife can shuttle 4 kids with one 4 dr car and get both of us to work! It's Monday and I start next Tuesday!

FYI: I'm an ex mechanic from years back and never had this issue with any of the imports I worked with before, I am capable to do anything so all thoughts are welcome!
 

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I've never heard of such a thing, but I'm not a mechanic. With that in mind, have you checked the check valve on the power brake booster. Maybe you're losing vacuum there or the booster is bad. I know proportioning valves can go bad, but it's pretty rare. The strange part is that you have no leaking wheel cylinders or calipers. I don't think it's a bad brake hose, or you'd have a wheel that would probably lock up or at least get hot on you. Maybe some of the members here can help you. Some of these guys are pretty danged sharp.
 

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Air leak sound is probably the power booster. That's the only thing I know that would produce an air leak sound. If the booster is bad or leaking, you should still have brakes, but as I recall the pedal will be super hard. Remember sound can be funny in trying to find where it's coming from. It bounces all over the place......
 

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Discussion Starter #4
Doug D said:
Air leak sound is probably the power booster. That's the only thing I know that would produce an air leak sound. If the booster is bad or leaking, you should still have brakes, but as I recall the pedal will be super hard. Remember sound can be funny in trying to find where it's coming from. It bounces all over the place......
the sound is definitely coming from the center or the back. I tried to unhook the booster to see if it would change but it still made the sound and the low to no pedal effort.
 

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The first step would be to determine if the van has ABS or not. The only explanation that makes sense is that there is air in the brake system somewhere though I've never heard air make noise in the system. It can be hard to bleed some cars, sometimes a vacuum pump or a very forceful application of the brake pedal during bleeding can help move the air.
 

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Discussion Starter #6
The van does have abs. I seem to be getting no pressure or only a little after pumping it up. I just took both drums of one looked like it had grease all through it . Im going to replace that side piston cylinder n see what happens. I pressed the brake w the drum of n nothing happened.
 

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Our old friend Pappy Gene had a similar problem with his PT Cruiser. Turned out to be a weak brake hose that was expanding under pressure.
 

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Grease on the linings? Or brake fluid? Either way, do NOT re-use those pads. Either fluid is leaking or you have an axle bearing that is leaking.

Air sound can only come from power brake booster, it may be bad.
 

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This is air in the lines. The noise from the booster is normal for large pedal travel, and a vacuum leak will just cause a very hard effort to stop the vehicle, but not cause the pedal to drop to the floor. I'd replace any leaking rear wheel cylinder, adjust the brake shoes to the drums, and have the system flushed and bled. As mentioned, examine all brake flex lines for cracks or bowing. Replace as needed. Noise midway through the vehicle could be related to the ABS pump since it is mounted on the back side of the frame cradle area. The pump may be trying to pump air (bad for the pump).
 

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If there is air trapped in the ABS pump, you may need a (sophisiticated) scan tool to cycle the ABS pump to bleed it.
 

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Is your ABS light on all the time?
 
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