mine was so bad at 1 point i had to accelerate down hill, and the paint of the pads caught fire lol, ive changed the piston and took the sliders out and gave them a brush with some wire wool, and replaced the piston bout 17 quid from toyota, make sure you grease the sliders before you put them back in and check the rubber gaitors for tears, this is most likely what wrong with it, if the rubber gaitors are torn get some new 1s of them because it will keep happening. instead of bleeding the whole system we bent the pipe in half and clamped up the pipe to stop the fluid coming out. my dad used to make brakes for a living so unless your sure about clamping up the pipe id deffo bleed them properly once its done