1991 Isuzu NPR 4 cyl Two Wheel Drive Automatic 145000 miles
My 1991 NPR is a Low Pro with 15.5" / 5 lug wheels on rear. I also have a 91 NPR for parts that has 16" / 6 lug wheels. My question is do I have to change the complete rear axle housing and all or can I change just the drums from one to the other?
There are two types of rear axles, single or double tires.
For single tire type, the lugs are on the axle shaft and you cannot replace the drum only.
For double tires, the axle shaft is bolted onto the hub via 6 holding bolts at center of drum. For this design, you can replace the drum only but you need to be sure that the diameter of the drums are similar. If not you would need to replace the backing plates as well.
If you are able to upload some pictures, that would help.