98 corolla brake problem

My Toyota lost pressure to its brakes and I replaced the master cylinder twice myself. Neither time worked. Thinking I was doing it wrong I took it to my car place and they also thought Master cylinder and tried 3 times before saying sorry and pushing me out the door. All the pads and rotors are new, there are no leaks and no air in the lines.

The brakes will work occasionally, but that isn’t really enough for me. =D Just suddenly the brake when you need it will press all the way to the floor with no pressure. Please help, I love my car.

Someone is going to have to get serious with the diagnosis on this. The system is fairly simple. What is interesting is that both independent systems must be failing which is very rare. Usually if one or the other divided parts of the system fails the pedal will go further to the floor and braking action will be reduced and the brake warning light on the dash will light.

Have the mechanic put a pressure gauge on the two systems and monitor the pressure when the problem occurs. If you truely have no pressure on both systems and there are no leaks, the problem has to be the master cylinder or something back to the pedal. It might be something with the pedal pivot but you would probably have felt the pedal moving if that were the case.

If you get this problem solved, post back the solution. This is a real head scratcher.

We took the car to a local Toyota dealer and their diagnosis is that all the lines in the car have gone bad from using non Toyota fluids. Brake, motor oil, power steering fluid. Is this something that can happen or am I getting had? I let my father in law take the car so they don’t talk down to me, I look quite young, and don’t have the car nearby to inspect the hoses/lines right now. When we attempted repairs all hoses and lines looked in excellent shape. Again, no leaks on inspection, or on the ground where the car has been sitting.