So I am replacing the front brake rotors on my truck. I took the cap off and there was no nut in the hole. I'm not sure what the nut is for or why it's gone (manual and YouTube both show a nut in that slot). I do know I've been driving around for 8 months without it though. How crucial is it for me to get a replacement?

 

Nut in the hole? I'm sorry your going to have to be a little more specific

 

In the middle of the shift there is a hole. It is threaded and in the video on YouTube I am referencing he pulls a bolt out of there. (1985 Toyota 4x4 Pickup - Front Brake Rotor Change, YouTube user BusaBob's Racing).
In the picture it is that center hole

 

dont take this for gospel but i believe the hole there is for ADD style drive flanges and a bolt goes in there under the cap on the flange.

on locking hubs If you have the snap ring still youll be fine and a bolt isnt needed

 

ive only used that hole for threading in a bolt to pull the axle out far enough to get the snap ring on and took it back out

 

I'm not sure what its for but every solid axle truck I've has had it and all my trucks are manual hub.

Like posted above it comes in handy when putting the snap ring on to keep the axle from sliding back in.

 

On my 84 there is a bolt that does the job of the snap ring found in the aisin hubs. Basically it holds the driveshaft in place.