Remove the end cover on the differential and measure the ring gear (the larger one) I believe they are about 7.5" and you should have a new gasket or gasket maker on hand also 80 -90 sae weight gear oil and if the rear end is limited slip you must add a small container of GM additive to the rear end as well.
There is actually a little bit more info needed: 2WD OR 4WD, Ring Gear size, 7-5/8 or 8-1/2, What ratio? GM option code: GU4-3.08 GU6-3.42 GT4-3.73. However It wont be a direct fit to a 2000 blazer only 1995-1997 Blazer only. For 1997 makes a difference with or with out AWD, along with with or with out ZR2 option.
There are two sizes of ring gears on small block chevies. You probably have the starter for the large ring gear but need the starter for the small ring gear.
count your teeth on your ring gear <big gear> and on you pinion <little gear> and the divide the ring gear teeth by the pinion
41 teeth on the ring gear, 10 on the pinion gear.
The best way is to count the teeth on the ring gear and divide by the number of teeth on the pinion gear. Or you can count the number of turns of the pinion it takes to get one full turn of the ring gear. For example, if we divide a ring gear with 41 teeth by a pinion gear with 10 teeth we find that the gear ratio is 4.10:1 (41/10 = 4.10).
43 ring gear 14 pinion
These cars came with a 10 bolt, 8.5" ring gear and an optional 12 bolt 8.875" ring gear.
ring gear 41 pinion 11 41/11 = 3.7272727272
There are four ways to find a ratio. 1 A dealer can normally tell from the vin number. 2 There are normally tags or labels on the axle that have part number, gear ratio, and fluid requirement info. 3 You can count how many times you have to turn the driveshaft to get one complete turn of the tires. 4 You can divide the number of teeth on the ring gear and divide by number of teeth on the pinion.
There are four ways to find a ratio. 1 A dealer can normally tell from the vin number. 2 There are normally tags or labels on the axle that have part number, gear ratio, and fluid requirement info. 3 You can count how many times you have to turn the driveshaft to get one complete turn of the tires. 4 You can divide the number of teeth on the ring gear and divide by number of teeth on the pinion.
It is a pinion gear.
ring gear