My guess is you have air in one or more calipers on one side of the car. When you hit it hard, things "pump up" and settle down for a short period of time.
I'd start out with a brake fluid flush and bleeding of all 4 calipers. While that's being done, have tech see if any are hanging up or losing fluid.
Last edited by Mike Richards; 07-26-2002 at 10:36 AM.