I remember changing a U-joint at the slip yoke in a 1971 El Camino, on the shoulder of Interstate 5 just outside of Williams, California. Using one of those "stick it in the slot" bumper jacks to get the job done. Every time a tractor-trailer zoomed by... the car would rock back and forth and the foot of that jack stand would scoot on the pavement!
I was 19, in the US Navy, and headed home on leave from San Diego. I'm lucky to still be here after that experience.
Gary