3100, this is a quote from the Chevrolet shop manual:
1. Remove door assembly by removing trim panel and lower hinge cover and disconnecting door assembly from hinge straps.
2. Scribe location of the upper hinge on the cowl pillar and then remove upper hinge assembly by removing the hinge body to cowl pillar bolts. (These are the three bolts holding the hinge box to the body).
3. Place the hinge assembly in a bench vise and remove the hinge pin.
4. Rotate the hinge strap out of hinge box and remove hold open device.
5. Install new hold open device, rotate hinge strap into the hinge body and install hinge pin.
From that point on, its just the reverse of the removal procedure. The reason I jumped on this is that we just completed replacement of a set of the hold opens on a hinge on my 50 3100. After chasing errant springs all over the shop for half an hour, I came to the shop manual and found out how easy it is if you do it the right way.
Hope this helps.
