2000 durango

Last Thursday I bought the truck. Before purchase the owner was to fix the braking system, which he did. I have the part receipts, and there is evidence of the work. He replaced the master cylinder, brakes, brake lines, and 1 rear wheel cylinder. the car stopped fine for 3 days. Now I have very little brake pedal, and very little stopping power. Any suggestions? I see no evidence of brake fluid leaking anywhere.

Try bleeding the brake lines. Begin with the furthest tire away from the master cylinder (passenger side rear tire) then next rear tire, then front passenger side, then driver front. Have someone pump the brake pedal 4 or 5 times after you loosen the bleeder screw behind the brake caliper. Once you have a steady flow of brake fluid coming out, close the screw.

Good luck!