Twice now I went to autozone for a simple set of u joints for my K5. One time I got the brute force one and installed it. It slid back and forth in the yoke! The out to out measure on the caps was just over 3 5/8". I measured between my yoke "ears" and it was designed for a 3 3/4" u joint. I went back and got the greasable version autozone sells. Turns out that was the same. I went back today and complained and tried ot get the right one. They didn't help, offered some at the time good advice that maybe someone had changed the yoke since the guy before claimed to have rebuilt the rears. On a whim I went to napa, asked for the samething i asked for at autozone and surprise they came back with the 3 3/4" u joint I need! INstalled it and that was that. There is a lot less vibration now but I believe my pinion bearings are shot cause it still vibrates pretty well.