Sometimes car doors sag because they are heavy, and the metal tends to stretch and weaken with use. Replacing the hinges will usually correct the problem. It's not an easy task, but it isn't necessarily difficult either. Doing it yourself will save you a lot of money because the parts (hinge and bolt assembly) will only cost $20 to $50, whereas labor will cost double that per hour.
First, open the door and prop it up on something or use a rope to tie the door frame to something overhead. Remove the bolts holding the hinge to the door first, then work on the bolts holding the hinge to the car frame.
If you do not want to take the hinge from the door and only want to replace the frame hinge, you can remove the pins holding the two hinges together. This way you can take the door off without removing the door-side part of the hinge.
To remove a pin, tap on it with a hammer until it begins to slide out of the hinge. Be sure to support the door as you remove this pin, because it is the only thing attaching it to the car.
Next you need to remove the remaining hinge bolts from the frame's hinge. Find the proper socket wrench and loosen the bolts. If you need to, access the back of the bolts through the interior of the car. Pull back the dash or interior walls to get at the door frame. Use vice grips or another socket wrench to hold the bolt in place while you loosen the nut.
Replace the old hinge with the new one. Line it up to the bolts and hand tighten. Then set the door back on the hinge and install the pins if you removed the pins (if not, just replace the complete hinge and door). Once the door is set and swings perfectly, finish the job by tightening the bolts all the way.
