Why does my car thud loudley when i puish or let off the brakes?

Really depends on the type of thud, so there could be a few reasons;

1. Disks are warped and therefore need machining. (Usually accompanied with a vigorous shake of the steering wheel.

2. Loose bolt on the caliper, can cause this loud thud when on and off the brake.

3. Loose bolt on the strut causing this thud. (although I doubt this but it is possible)

And again without hearing the sound it is hard to diagnose. Try to see where the noise is coming from while the car is in a stationary position.