How do I find out what diff I need to the back I have herd they need to match front and back with ratio ???

 

 

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Look on the gearbox bellhousing near the starter motor, they're should be a ty###  number on a white sticker .

Give this a Google to find out the box's ratio then buy a diff with the same ratio .

Other than ratio there's two main types of diff r160 all early classic and newage wrx 's / r180 later classic sti and newage sti's.If your unsure what r number the diff is give your year and model a Google to find out what should be in there .