My son aquired my '89 Bronco this summer and had no problems until about 2 weeks ago. Apparently, while driving, his brake pedal went to the floor and he lost system pressure. There's plenty of fluid in the system, and the brakes will bleed just fine. There are no visual leaks. I've been trying to find out any solutions before I go replacing parts just to find one bad one. That could get pricey. Any thoughts?
Thanks for the help,
Brian

 

A failed or failing master cylinder will not be a sudden pressure change but you WILL feel the pedal "fall" under your foot if you hold the brake. This makes the most sense if the system doesn't appear to have lost any fluid but doesn't fit with the symptom of it being a sudden occurance. The "nice" thing about a master cylinder dying is that it will give some warning before failing completely.

No "visible" leaks... have you gone back out and taken a look at the bottom edge of the drums on the rear lately. Sometimes a blown wheel cylinder in the rear will take a bit for the fluid to seep down to the bottom of the drum before you can see it. If there is still no visible sign, try removing the drums long enough to inspect them for moisture inside. Again, with no apparent fluid loss, there should be no leaks theoretically.

 

I have heard of such rare occurance. I found it while doing research on Bronco's before I bought mine. It is an unknown problem and has been posted by ford as to take caution as an unknown and very rare occurance. Not sure if there was a service bulletin, but it is a known problem. Have you checked the pivot points under the dash to be sure that they a connected and that the pedal arm is connected properly? Also check the BPA Brake Pedal Applied switch either Hydraulic or electric located in the master cylinder

 

another things youcould check is the vaccum line for the brakes should goto a vaccum tree thats what heepen to me when i rebuilt my moroto forgot to hook it up hehe, could be leaking. my guess though is you master cylinder.

 

I've only had one time when I lost my brakes all at once, when the inner brakepad fell out and the piston had to go all the way out to reach the rotor.Afterwhich the piston pushed against the rotor and the pressure came back. Seemed like everything was ok untill I found out about the missing pad.