Does this video explain it pretty good? Why is he making marks and counting the threads?

 

That is the backyard way of changing the pinion seal. He is counting the threads and realigning the nut to get as close as possible to the previous torque and crush value. You can do it this way, but there is no guarantee of it lasting any length of time.
Doing the job that way he does not even verify proper gear pattern by pulling the cover.

You are suppose to install a new crush sleeve then torque it properly to ensure the preload on the pinion bearings are correct. then you should pull the rear cover and use marking compound to verify the ring and pinion mesh correctly.

 

Ok I'm going to attempt to replace this seal. Whats the size of the nut holding that pinion ?

And is this the right seal ? http://www.oreillyauto.com/detail/ma...ttr_10039=Rear

And how many oz of gear oil does the rear end take ? It's 80/90 oil right ?

 

Good luck, hope it lasts.

 

I know you suggested to take it to a shop but I simply can't afford it with no job or money, so my cheapest route is to do it myself. I start school for automotive tech on the 23rd of this month and this is my only means of transportation.

 

I understand its expensive, but if you cant afford to fix it correctly and you rely on this truck daily i would just keep the fluid full as long as it is not leaking very bad. then fix it properly when you can.
The chances of you doing something wrong and causing the rear diff to fail are very high if you dont know what you are doing. I have seen these things fail and put a pinion through the cast iron case.

Or just go to a junkyard and find another 4x4 differential with the correct gear ratio and swap the entire assembly. might be cheaper than trying to fix what you have especially if the one you have is already making noise.

 

OK . because there is no fluid on the ground I'm going to assume the leak isn't bad. I'm going to check the fluid level and fill it up. How many oz does it hold ?

 

Also, can low fluid cause bad acceleration and truck vibration ? Should adding fluid fix those issues ?