brakes compressing on their own

The bronco project has finally gotten to the point where it can drive around the neighborhood on its own power. What has surfaced is a strange brake problem. It has the astro hydro boost with late 70’s corvette master cyclinder. Disc front and rear, stock ford calipers on the D60 and ½ ton chevy calipers on the rear 14bolt. The steering is a PCS full hydro set up.

The problem – drove it this weekend, maybe 2 miles, and the front brakes began to clamp down on the disc with out pressing the brake pedal. The engine was running a little warm but I don’t think it would be to the point that the brake fluid would expand and compress the pads? Also, the brakes have been bleed multiple times and still have not been able to get rid of the spongy pedal but still work rather well.

Has anyone ran across this scenior before? Any input/help is apprciated. Thanks

I've seen a dodge do something simmilar. If you turned the wheel and called for hydraulic pressure the brake peddle would go down. There ws some sort of blow by inside the hydro boost. I would start with a new hydro boost unit.

I wouldnt rule out return line pressure that is appling the hydroboost. Make sure that you aren't building pressure on return . What kind of pump or return system are you using ?

Make sure there is slop or a slight bit of play in ALL brake linkages and push rods. pedal to hydro and hydro to master.any pressure on them will set the brakes.

I had to put washers between the MC and booster to space it out to keep the pressure off the push rod.

It is a PSC P-pump from a full hydro steering kit.

I'll take a look at the slope/linkages between all parts tonight. Thanks!

TBS, thanks for the suggestion. Add some space between the linkages and no more self compressing brakes, thanks!