87 voyager No brakes

[emk1198]

I replaced the front brake pads on my van and since then have had no brakes. When the van is not running the brake pedal is solid but as soon as I start it up the pedal goes to the floor. I have replaced both calipers, brake hoses, wheel cylinders and the master cylinder twice. I also disconnected the vaccum line from the booster and plugged it which then gave me a solid pedal. Any suggestions would be appreciated.

[GTP Dad]

Welcome to AF!!

When you changed all that hardware did you bleed the brakes? If not bleed them now and the brakes should work better. If you did, did the master cylinder run dry? If not you may have a problem with the master cylinder itself or the booster.

[jsinton]

It's either your master cylinder is toast and needs to be replaced, or you have air in the lines. Changing the master cylinder will also force you to bleed the brakes, and it can be bought from Autozone for $20.

[emk1198]

I bled both master cylinders when i replaced them and bled the whole system out at least a dozen times. How can i tell if booster is bad?

[ronmar1]

If the booster is bad the brakes will be firm all the time. Go to the farthest brake from the master cylinger (the right rear) and bleed from there first. You must surely have some air somewhere. Either that or you have a bad leak or an expanding rubber line.
Ron

[emk1198]

I have bled the system that way twice. There's no fluid loss anywhere and I replaced both brake hoses all ready. What's the chance of me getting two bad master cylinders?

[RIP]

To check the booster let it run a minute then shut it off. Now apply the brakes. You should have resistance for at least two or three applications. If the pedal sinks to the floor right away, either the booster is bad, it's vacuum source is leaking, or the check valve is bad.

http://www.howstuffworks.com/power-brake1.htm

[jsinton]

Ya know, when I did my master cylinder, I had to pump brake fluid for about an hour before I was satisfied. Probably I pumped close to two quarts. I was still getting air long after I would start pumping. I bench bled before installation too. Did you bench bleed?

[RIP]

To follow with jsinton's thought, read the third paragraph here: http://home.teleport.com/~cosa/vap/tech/bleedbrakes.htm

[emk1198]

Yes, I bench bled both master cylinders before installation

[emk1198]

So I have tried everything listed above and I still have the same problem. Since the problem started before I broke open any brake lines, I think what I am going to do is wait till I get a junker that has a working brake system at the garage I help out at and swap the master cylinder and power booster off of it and go from there. That way I know I'm working with working components.

[webbch]

The cheapest solution may be to bring it to a shop and have them bleed the brakes for you, since all indications are that you have air in the system. If that fixes your problem, it indicates your brake bleeding procedure was flawed. Watch them when they do it and see if their procedure is any different from yours.

When bleeding, are you using a vacuum pump at the caliper or do you have a helper in the vehicle doing the "up, down" ritual? I have a MityVac vaccuum pump that I've never felt comfortable bleeding my brakes with. I've tried it several times, but I dont' think it flows enough volume to really pull all the air bubbles out of the system, even when I'm very careful to get a good tight seal on the bleed nipple. I HATE needing a helper while working on vehicles (and my wife hates it too ), but bleeding brakes is one job that I feel really needs another person.

[jsinton]

One thing I noticed when I did my master cylinder was that the brake lines to the front caliper were loose. Make sure your rubber brake lines are bolted down tight.

[emk1198]

The proportioning valve was either bad or blocked. When I applied the brakes I had good pressure out of the master cylinder into the vavle but no pressure out of the valve. Thanks for everybody's help

[RIP]

You have reminded all of us to keep the prop valve in the mix. They so rarely go bad you just don't think of them. Thanks for posting your fix. Cheers!