Gears & Axles - Rear End

Hi

If I wanna rebuild my rear end I need to change the diffs and the axles only ?
whats the difference between a carrier,truetrac and a spool ?

thanks

To rebuild it you need all new bearings and seals. A spool locks both wheels together all the time usually used in drag only cars. The truetrac is more like the stock posi. If you have a stock rear I would not suggest putting a bunch of money in it I would just put the money to a better rear that wont break