I've seen this twice now and I admit that I am stumped. I've seen this on a Ford and a chevy.

On the chevy we replaced the master cylinder and installed new pads. During installation of the pads we were unable to bleed the left front since the bleeder was corroded and rounded off. Guy drove it a while (6 months)and the left front locked up. They pried the piston back and drove it 6 more months. That caliber never worked again and during braking the truck pulled to the right. I replaced the left caliber and was surprised to see that the pads were 2/3 gone in less than 10,000 miles on the left front. After installation of the new caliber - it locked up! I was torqued. I released the pressure in the system and bleed it again. It still would lock up. Bleed it and bleed it. Finally had the guy drive it around the block. It worked. 2 weeks go by and he hits the brakes hard and the left front locks up. He had to drive it two blocks untill the thing unlocked. I assume there is a blockage of some sort in the rubber hose that is not allowing the piston to retract. Other than that I am stumped.

The Ford is a tempo that is having the same problem on the left front but has not had any components replaced yet.

98 F250LD 4X4
Slotted Rotors

 

It sounds like the piston is bent or rusted or real old and used up. In either case the piston binds up inside the caliper. not much you can do about it. if the piston bore is worn, a rebuild kit won't help. The most expensive caliper I have seen was $112, it went on a Porsche 911. The Chevy cant be more than a dollar or two. (well, thats what there worth)
try forddiscountparts.com

I would replace them.
I'll sleep better knowing you can stop at the next red light:-)

 

I've seen one other possibility, and it's a a slim one. The flexible hoses that connect in the wheel well to the caliper sometimes deteriorate on the inside. If they crack or flake, the pieces can act like a check valve and do a pretty good job of holding pressure on the caliper in some cases. If it isn't in the caliper, change the hose, and check the caliper for pieces.

Good luck,

Paul

 

Thanks for the replies. Since we replaced the caliber (chevy charges $40 for their junk) I would assume that it is the brake hose inside the wheel well.

98 F250LD 4X4
Slotted Rotors

 

It could be something hung up at the master cylinder. Why not crack the front brake line at the master cylinder when you have lockup and see if that releases the pressure?

 

I wish it was the master cylinder, but since it has been replaced on the chevy and no change. Additionally the chevy only has two lines off the mc. So if there was pressure it would affect both front brakes, right?

The Ford has a seperate line for each brake coming from the mc. But I would still expect some other performance problems to occur before one caliper locked up.

98 F250LD 4X4
Slotted Rotors

 

I had this same problem too, but on another vehicle (a vw bug)
I did the same thing you did, and the only thing left was the
rubber brake hoses, what I found was the inside of the hoses
collapses, only lets fluid into cuz it's under pressure by the force of your pedal but would not let the fluid
return cuz the spring in the wheel cyliner (vw has brake drumsup front) was not strong enough to return the fluid through the collapse hose just like a check valve, and in your case your calipers too probably isn't strong or forceful enough to return
it either, not saying their bad or anything, try removing the hose
and blow in it from both ends, you should be able to blow thru it
if not then you found your problem, and brake hoses are way cheaper than the master cylinder..... just my 2 cents.

 

 

Locked up caliber

 

I would strongly consider Mics advice. I've run across the same problem on chevy p/u's before, and that fixed it (finally). they're cheap and could probably stand replacing anyway if they haven't been. And it's caliPer, not caliBer (sorry, it was bugging me)