For what it is worth: Maybe someone can learn from this experience.
On my 86 SDL, I have had problems the past couple of years with vibrations. Initially, it seemed like tires, and i'd take it in to the tire shop, and they would find slipped belts and sell me a new tire. This got very old, Last fall, we changed the carrier bearing rubber mount. that seemed like it took care of the problem for a while, then it came back.
Friday night, we put it up on the hoist, and checked things out. everything seemed ok. Carrier bearing looked good, axles tight, and tires reasonably round. I climbed up a ladder and started the car and ran it up to 60-70 mph. Vibration there. Switched positions, and my brother ran the car up to 70mph. Driveshaft was smooth as silk. no bouncing tires. The left axle shaft looked normal, but the right one was moving back and forth along the centerline, toward the dif, then toward the tire. I pulled it out and the outer end is stiff. Inner end seems to be normal. Since i didn't have a spare axle, I pulled the boot and pumped some grease in, then put it back together. Theory that grease can't hurt a stiff joint, and it might loosen up while i try to find a used axle. I have never seen an axle fail in this mode. I have only seen them get loose and rattle around. (still annoying)
IN the process, I found out that all 126s are not equal. My 126 junker has the 123 style axles, that you have to pull the diff cover to unclip. THe SDL has the newer style.
