But when you buy another one, your're buying a pig in a poke. Even if it sounds OK today (to untrained ears), they can go bad overnight (right?).

I'm trying to train my ears to recognize the sound I have and aviod it.

I'm wondering how prevalent the pinion problem is in the 63-68 population. If 50% of that set has worn/noisy pinion and 25% of the 69-76 set has it, I will start looking for a 2.76 from a newer car.

Is it impractical to buy a used 1965 rearend because it is more likely to go bad than a 1975?

No, usually major rear axle problems do not happen overnight. They tend to start quiet and gradually grow louder (unless all the oil leaks out, in which case they grow louder in a hurry).

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Too many people who were born on third base actually believe they've hit a triple.

Is it impractical to buy a used 1965 rearend because it is more likely to go bad than a 1975?

No.

There's really no heuristic that is going to let you predict which rear axles are likely to be good and which to be bad. At this late date, there is no practical difference on the whole between 30- and 40-year-old rear axles: some of them will be good, and some of them will be bad. Either test out the one you want to buy, or get a guarantee, or get a price low enough you can afford to have it refurbished.

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Too many people who were born on third base actually believe they've hit a triple.

Yup. gave away 2, 7-1/4s and scrapped a 3rd (all F body) a few years ago cuz I was tired of tripping on them, I tried to sell em, couldnt get any takers for even a measly $25. Nothing was wrong with them (yet). 7-1/4s are junk! Blew the one out of my 90 Dakota, cracked the carrier when a busted spider tooth got wedged between the other spider and side gears. Even my mom who never drives faster than 10 UNDER the posted limit, blew the one in her 5th Avenue to smithereens. Replaced them both with 8-1/4s. A 7-1/4 may be worth a hoot with a Sure Grip (not sure though--- seen pix of them but have never seen a sure grip 7-1/4 in person. Find at least an 8-1/4 or even an 8-3/4.

How times have changed! I called All American Classics and Wildcat one week last month and they were cleaned out.
No 7 1/4 rearends with 2.76 (or 2.93)!
I couldn't believe it, so I walked through the 20 or 30 A-bodies that AAC (in Vancouver) had in their yard.
They looked like the same 20-30 I saw a few months before, except all the 7 1/4 rearends were missing!
Some guy is making trike motorcycle conversions and paying $150.

Why would you buy a new vehicle that had 40 year-old parts, and why wouldn't you build a new rearend from scratch with new parts if you were building fancy trikes for baby-boomers??

So the cream of the crop is getting shipped to this guy on pallets and the questionable ones are sold for $150-175 the the local suckers who drive /6 Darts and Valiants.

It is a shame that you are not closer I could hook you up with a good one cheap.
I took it out of a 73 dart about 17 years ago and it is complete from drum to drum and run quiet down the road.
Shawn

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1971 D100 SWB Step side, 225, 3 on the tree, 3.91 gear