i have an 87 sami  i had a u-joint let go to today and it trashed the short piece of the rear drive shaft.
so i was wondering if i could take that piece off a front drive  shaft
r the drive line splines the same front to rear?

Been there, done that.  You can take the "ears" off the end of a front (remove the u-joint), and use them in the rear (with a new u-joint).  Consider that your rear shaft may have slipped out, bent backwards, and destroyed the "ears" when it bent over and broke the u-joints with it.

the ears on the flange side are undamaged its the short female part  of the shaft that is all messed up
i was lucky i felt the u-joint brake on the free way i pulled off then seen the ear on the shaft was all bent from the joint brakin


i hate china made parts!!!!!!!!!!!

Always go with either stock replacement or the Mitsubishi joints that Trail Tough has available.  We have learned that lesson a few times.