My 97 Astro (~110K miles) developed a leak in the brakes lines running to the rear of the van. I had these line replaced, and ever since the brake has been stiff - a lot of effort is required to slow or stop the van. I took it back to the mechanic, who determined that there was no air in the line. We discussed the "check valve" - not his words, but mine, that prevent complete loss of fluid in the event of a leak, and he indicated that this must be working properly because the Brake light would otherwise be on.

Ideas?

Is the power steering working?

Yes, the power steering works fine.

Your vehicle has a system called "Hydraboost". It uses hydraulic fluid pressure provided by the power steering pump for both steering and brake assist. That's why I asked about the power steering.

The "check valve" is actually a proportioning valve. It is designed to shut off the flow of hydraulic fluid in the event of a pressure differential in the two circuits, (front & rear brakes). The valve has a switch that turns on the BRAKE light on the dash telling the driver there's a problem, (no kidding!).

A hard pedal with excessive effort to stop the vehicle, is an indication that only one hydraulic circuit is working. It's possible that the electrical circuit is not turning on the light and you are in fact using just the front, or just the rear brakes. To check the switch, ground the wire at the proportioning valve, the BRAKE light on the dash should turn on.