does anyone know wut size gears r in the in the rear and front diffs. i want to upgrade the gears but im not sure wut size r in there...if anyone knows that would be great thanx.

 

That would depend on which Blazer you have.
The ZR2 have a larger rear axle then other Blazers. Pretty sure regular Blazers the front is 7.25" and the back is 7.625".

Give the guys at Randy's Ring and Pinion a call, they will know and will know what size gears you need.