Recently on my 1991 Ranger, the slave cylinder went out, and after I took everything apart and put it back together, the speedometer wouldn't work. Looking at it, I found that whenever I insert the speedometer wire into the port, the needle would instead of going in the square slot, just recede back into the cable. Is there anything who knows how to fix this short of taking the whole cable out?

 

Check the other end of the cable, at the transmission, or at the back of the speedometer.
One end of the cable has been pulled off or been broken off, when you removed the transmission.

A speedometer cable has the sheath(outside cover), '91 should be about 72" long, the cable inside the sheath will be about 74" long and it is not attached to the sheath, so can slide all the way out on some models.

So if one end of the cable is disconnected, or broken off, the center cable can be pushed back inside the sheath.