brake bleeding

[quickcampbell]

First time post. tried to search for the answer and just cant find what I need. I have a 1995 bronco and I recently replaced the ball joints, shocks, driver side rotar and put new calipers on both sides. During this process I broke a sensor on the pass side Im assuming it was abs. I did not replace that sensor. I went on to bleed the brake system and it will build pressure but wont hold it. brakes get spongy after 30 seconds or so. If I crank it up the pedal goes almost all the way to the floor and makes a wooshy sound when I push on the brakes. Ive bled the **** out it, going master, front, back. Im getting clean fluid, no air, and cant find any leaks. Is that sensor causing this, or is there somthing else I need to know to get my monster growling again. its a daily driver for me and Im hoping to get in back on the road asap so any help is really appreciated.

thanks,

quick.

b-(

 

[BroncoJoe19]

What year is your rig?

I'm guessing '96.

IF I understand you correctly, you can pump the breaks, and the pedal will rise, but if you hold steady preasure on the pedal it will sink to the floor?

You may need to rebuild or replace your master cylinder. I've read that bleeding the brakes with the two person method (where one pumps the pedal, and the other opens, and closes the brake bleeder) will sometimes destroy the master cylinder. THere is a plunger inside the master cylinder that slides within a cylinder back and forth during normal use. However it NORMALLY only travels a certain distance, and crud can build up where it doesn't normally travel. When one bleeds the brakes with the two man method, one will push the pedal to the floor, (and the plunger to the ends of the cylinder over the crud buildup) and tear little grooves into the plunger, which then permits brake fluid to bypass the plunger, thusly creating an internal leak.

There is another (but less likely) possibility that the ABS system is at fault. I am unclear exactly how it works, but there is a pressure release valve in the abs that sometimes gets stuck open and leaks pressure back through the system giving the same symptoms. You can probably find info for that at our pal miesk5's site www.broncolinks.com

 

[madmax]

I agree, probably master cylinder at fault there, you can rebuild them, and they arent't that bad to do. But if you decide to replace it, avoid any cheap tiwanese parts there, It's something WAY too critical to risk having it fail, mine did and i limped it to the local napa using the e-brake.