Saginaw Driven Gears

[BMERDOC]

So I was doing more stuff to my truck after work today and deceided to take a look at my inop speedo. To eliminate everything but the trans i intended to remove the cable from the trans, chuck it in a drill and spin it. When I pulled out the cable the stalk of the driven gear was still on the cable and the gear itself was still in there. My question: Did something else cause this or is it well known that they break like this? I don't wanna order one without solving the cause first. BTW, it looked white. I saw that there is white, yellow and grey options and look like they might be confused as they age. I will recheck the color before ordering I just wanted to see if anyone had any input. Its a 3 speed Saginaw.