66 barracuda driveshaft shortening

You can tell because down by the tail of the shaft (near rear end side) it looks like one tube ends and another starts inside that tube with like a 3/8" gap between the tubes. I think is is filled with a rubber for vibration or something. Saw a lot of them on Darts in the mid 70's if my memory serves me even 1/2 way right. I just junked them and had a new well build drive shaft made.
Sorry no pics.
Joe