I have a 1998 Tacoma that the front brakes are dragging. I have replaced the Calipers, Rotors, Pads and the flexible lines from ther chasis to the Calipers. When I start driving the brakes are spongy but the pedal soon becomes hard (within 10 miles. I have talked to the toyota mechanis and they are stumped! My truck does have anti lock brakes and I am wondering if this could be the problem?
Any suggestions on what would cause this and how and average airtcraft mechanic schmuck like myself can fix this???
You have not mentioned if you changed the master cylinder. When the front brakes start to drag, crack the line to the front brakes at the master cylinder and see if the drag disappears. If this occurs try rebuilding or replacing the master cylinder. While you have the master cylinder off check to be sure the push rod from the power brake unit is not extended too far.
Let us know what solves this problem.
I have not replaced or rebuilt the master cylinder. When I crack the brake line to the front wheels will the fluid drip out or spray out under pressure if the master cylinder is bad? If it is the master cylinder is this caused by a weak return spring or bad check vavles? What should I look for in the master if choose to rebuild it? Have you heard of similar problems as this with other Toyota Tacoma owners?
did you bleed the brakes, in order; right rear, left rear, right front, left front?
even though the fronts were the only ones done, you should bleed all of them. also, this is a good time to put new brake fluid in, as you bleed them, to change out the old fluid.
i would suggest the toyota mechanics are stumped, because they want you to go to the dealership. i have not had much luck getting real helpful info from dealership mechs, service advisors because they want the work! (of course this is excepting from THIS forum of course!) 
did you by any chance adjust the brake pedal lock nut, in the process of doing this work? the rod the nut secures adjusts the ‘throw’ to the master cylinder. also, if the rod was (mis) adjusted you wont get all the air out of the cylinder when you bleed the system.
I did not make any adjustments to the Lockout rod and I did bleed the brakes in that order. The thing that has me stumped is that the pedal is spongy when I start out in the morning (engine cold) but with a few miles is can stiffen to where there is on a 1/4-1/2 inch of throw before the brakes will lock. This is also an iintermittent problem as it does not happen in the same manner or time frame with any consistancey.
What would you suggest for troubleshooting proceedures?
dont take this personally but… are you sure you are confident tht you are competent in bleeding the brakes? it sounds to my ‘ear’ that there is still air in the calipers.
i can share some experience with my successful, (and some not so successful) brake bleed work.
the bottle and hose method are best for one man brake bleeding. the bleed screw should only be opened about a 1/4 turn (air does suck around the threads, even though it seems tight)
the difficult part of this is knowing when enough is enough. and you cant SEE if there are any bubbles coming out or not, and conversely you cant see if the bubbles are getting sucked back in the screw. (and NOT sucking all the fluid out of the reservior is a trick in itself.)
and (if available) a two man, pump and tighten the screw after each pump (before letting up on the pedal) method is best.
are you sure you got the calipers on the correct side? if the bleed screw isn’t on TOP, all the air can’t get out. (i m not sure of your calipers, if they are symetrical or not!)