YOOLK?

If the yolk you're referring to is for the driveshaft, it's the splined part that slides into the transmission, and attaches to the output shaft. The slip yoke on your driveshaft isn't typically a part that goes bad, however they can wear out over time, being a rotating part. A lot of the time, they usually take out the tailhousing bushing, too, so that might also be worth looking into.