Didn't Make It Home From Carlisle

I have a 2 1/2 hour drive home from Carlisle. On the way home my 72 D100 stalled going down hill on the turnpike. I just put it in N and started the 318 back up. An hour later it happened again going down hill on route 56. This time I pulled off the road because it wouldn't fire up while rolling. After about the third try it started and stayed running so I tried to make it home, about 20 more miles. Ten minutes later while going down the the Johnstown bypass it stalled again. This time it fired up while rolling and after a few seconds it backfired and shut off. The backfire sounded like a gunshot, very loud and violent. I pulled off the road. It would start but it would make a clanking noise. This noise didn't speed up when I would accelerate the engine. I put it in gear hoping I could limp down the road to a safer spot. When I put it in D it would go forward clanking then die after a few seconds. I put it in R to see if the tranny was working and it would limp backwards. There was no noticeable damage or leaks from under the truck or under the hood. I had it towed to a local garage. I am going to check it out tomorrow. What would cause such a loud and violent backfire? Did this violent backfire cause some damage? Anyone here ever experience anything like this? What do you guys think? Thanks FABO.

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Sounds like a bad points condensor, but isn't that thing electronic?