72-75 have the most brittle problematic frames of all CJ's made. 76 the design changed and so did the metal. When checking a 72-75 CJ for a potential purchase, examine the entire frame very carefully and even after you own it. Look around the spring perches, at the attachment welds at the front crossmember just behind the bumper, and especially the steering box mounts. The very best years for any CJ ever were 77,78 and 79. If one were fortunate to find one with an Inline 6 you most likely will find the 6.32 low first gear T-18 4 speed behind it. Coupled to a dana 20 transfer case mounted in front of a Corporate model 20 rear axle. You have one of the best packages found in a factory built rig. Drop some one piece axles in that rear end and you have a rear axle that is stronger than a dana 44. The ring gear tooth is longer than a dana 44 ring gear. The weak point on an AMC 20 axle is the housing and it's two piece axle shafts. It has thin housing tubes. The wagoneer AMC 20 has much thicker tubes and can be shortened for a CJ app. The 77-79 cJ's also came with a disc brake dana 30. The brakes in those three years are more stout that other Jeeps with disc brakes. The rotors in a 77-79 are 1 1/8 thick like the IH scouts and all the other year CJ rotors are 7/8 thick.
Dana 30 axle shafts are induction hardened and in 39 years messing with CJ's doing rubicon 11 times and many other popular trails over and over, I have never once seen a dana 30 shaft break. It is typically the axle U-joint that fractures and takes out the ears on the shaft from the shock and broken parts under torque.
Aside from the frames on the 72-75 jeeps, the rest of the rig is just great.
If you are looking to get into a CJ be aware of what has been said already.
I would highly recommend finding those three years I mention as the jeeps are built as stout as you can get from the factory and with minimal mods you can make a potent trail rig right from the start. On a final note the 77-79 CJ's with V-8's typically came with the T-15 three speed. Some early 74 and 75, 76's came with the much sought after 4 speed T-18, but they were only a 4 to 1 first gear. You must check it verses taking someones word for it.
I'd take a 77-79 6 cylinder CJ any day. All I really care about is 71 and prior. Essentially a kaiser built jeep. I know full well better jeeps were made later. But a kaiser built jeep is my weakness.
Thats all In can get in here. My dinner is ready.
Good luck and wear a seat belt.