Sounds like a sensor wire is going bad. As you brake the sensor wire bends and probably looses contact somewhere. Solution is to test the sensors by jacking up the car and rotating the wheels while measuring the A/C voltage produced by the sensor. If this is too techincal you're local shop can handle. Once you see the voltage output by rotating the wheel bend the sensor wire to see if it drops to no voltage. When the voltage drops to zero the ABS computer thinks the wheel has stopped rotating and starts to lower the braking pressure to start the wheel rotating again. Good luck John