You need a reference point to measure the amount of bend. It doesn't take much of a bend - probably less than 1/4" and maybe only 1/16" to 1/8". It will depend on the hinges used and your truck.
Measure the hinge before you heat and bend it. I clamped the strap in a vise and placed a straight edge along the top edge of each hinge strap over to where the big reverse bend disappears into the hinge body (photo J).
You can just eyeball the gap (if any) and judge how far to open or close it. Now, heat the hinge with a torch to dull red, give it a little bend with your wrench, and then grab your straight edge to check the change. (Don't burn yourself. You're wearing gloves, right?) If you went too far, quickly bend it back the other way and recheck.
Once it cools down enough to handle you can bolt the hinges (all the way up in the slots and tight) to the cab and test fit the door. Leave the bolts loose on the door so you can move it around and very carefully close it.
Important reminder: A small adjustment at the hinge can translate to a large change at the other end of the door. If the striker is in place, remove it.
Lift the door up so that the belt line of the cab and door line up. Is the door flush with the cowl (or up to 1/16" proud)? Are you able to line the door edge up flush with the cab at the back or does it stick out at the bottom?
A door that's a tiny bit too far in at the top can make the bottom rear corner stick out. You'll get the opposite effect (diagonally) if the bottom of the door is in a tiny bit too much. The goal should be to have it flush with the body front and rear and that's achievable if the hinges are bent the right amount and the door isn't physically twisted out of shape. If you're not a glutton for punishment, then splitting the difference across some panel or gap is totally acceptable.
On this truck I ended up bending both Dynacorn hinge straps in till there was zero gap measured at our reference point with a straight edge. This made the leading edge of the door slightly proud at the cowl. We have tight gaps all around so this was warranted.
How and Why Bending These Hinges Works
Some of you may already know or figured out how bending the straps moves the door horizontally in or out of the opening. Sadly, it came to me while laying in bed at night thinking about it.
It has to do with pin location and geometry. Using the magic of Adobe Photoshop, here are two simulated images with exaggerated bends to illustrate. When the strap is bent and then swung back to where the 'closed' position would be (ie: parallel to the door), you can see the door is effectively repositioned. Notice, however, it will also tend to move the door forward or back slightly. Other adjustments can be used to compensate.
The actual bends you make will be much smaller and the amount of movement more subtle (photos K&L).
Fore, Aft, and Vertical Door Adjustment
These adjustments are covered in the service manual and film strip noted above and are pretty straightforward. I found there was plenty of fore and aft adjustment of the door on the lower hinge. There’s almost too much. But the upper hinge is much more limited.
If you need to move the door forward more than the upper hinge is allowing, there are a couple of things you can try - and slotting the holes in the strap may not be the answer!
It turns out that sheet metal inside the door will only allow the upper hinge strap to slide in so far. With the door on a stand, take note of where the strap stops when you slide it into the door. There's a stop that contacts the back side of the hinge arm. Some dimpling of the sheet metal here may help. You can also remove a little material from the back of the hinge arm where it contacts this stop (photos M & N).
The back of the pocket is also closed so the end of the strap may hit it. You can remove a little material from the end of the hinge strap. It may be necessary to slot all holes just a little towards the front (photo O).
Even with the hinges bolted to the pillars in the fully up position you may need more vertical movement out of the doors to get the belt lines to line up. If necessary you can slot all hinge strap holes vertically (photo O).
Removing just a little material here and there and checking the fit can net 1/16" to 1/8" or more of valuable adjustment for good alignment and even gaps. There's no need to get carried away or run amok with a die grinder.
And Finally...
On the generic driver side hinges, I welded up the oversized bolt holes and used a die grinder with ¼” straight carbide burr to restore them to the original shape and size. External tooth star lock washers will be used under the bolt heads. With a slight bend on each and the above mentioned mods to the other holes, the door seems to fit fine in the opening (photos P & Q ).
Final Tip: There’s a lot of trial and error testing involved. Run a 3/8”-24 (fine thread) tap through all holes before you start. It'll clean the threads of paint and corrosion and make running bolts in by hand faster and easier (photo R).
