the driver's door drops about 1/2 when I open it. the hinge pins appear to be loose. with hinges welded to the door and body how do we replace the pivot pins? Do we use an air chisel and drive them up from the bottom?
Below are the procedures I used on my 74 Nova to replace the door hinge pins and bushings.
It is normally the door hinge bushings that wear down and these bushings also need to be replaced with the door hinge pins to reduce/eliminate door sag.
To complete this task, I had to find a way to support the weight of the door so I could remove the 2 hinge pins... and then move the door away from the car so I could also R&R the hinge bushings.
Before I removed the door pins, I had to remove a small spring located just above the lower door hinge.
Since I was also working by myself, I tried to support the door from just the bottom, but that didn't work out to well because the door was too wobbly and unstable when only supported from the bottom.
I then used an engine hoist with a couple of ratchet straps holding the weight of the door and this worked fine. I looped the ratchet straps around the bottom of the door (one strap towards the front of the door - and one strap towards the back for stability) and raised the hoist to hold the weight of the door. I know this was probably overkill, but I used what I had on hand. I did not support the door by the window frames.
Once the hinge spring is removed and weight of the door was supported, I used a small hammer and a punch to drive out the pins... and then moved the door away so I could R&R the hinge bushings with the same punch and hammer.
Once the new bushings were installed, I moved the door back into position > installed both door pins > and reinstalled the hinge spring.
I have done the same thing as Rif. I used my floor jack to support the bottom with a 2x4 between the jack and the door and my lift to support the load. Once you lift and balance the door the biggest pain is the spring. Be careful installing the bushings, they can mar easily.