The problem i am haveing is when i get on the brakes the truck pulls to the left somtimes and them to the right other times. I have a 97 f150 and i allready replaced the front calipers and rotors and pads. didnt fix problem. next i replaced the master cyclnder. not the problem what else could it be

 

Sounds like tires.

 

bad tie/rods??, ball joints, tires, did you bleed the calipers real good i would start there and have them power bled with new fluid and remove any air from the system. Please let us know how it works out.

 

i power bleed the systems, also has new tirrods on the truck. it also does it with both sets of wheels and tires. Is there any way the Paportion block for the brakes went bad?? thanks

 

Could be the proportioning valve. I thought it controlled the front to back flow but its worth a try