Differentials - Buick used a 8.2 inch unit through 1970. Therefore to get a 8.5 inch unit you need to use a 71 and up differential. With 8.5 inch carriers you have to be concerned with two types of units as follows:

(a) Series 2 - for 2.XX gears and 3.XX up to 3.08, These may be identified with a casting numer of 410408 found on the passenger side with four large "8"s also on the carrier

(b) Series 3 - for 3.23 up to 4.10. These may be identified with a casting number of 410409 and three large "9"s on the carrier

Light duty units have two spider gears and heavy duty units have four spider gears.

Here are the axle codes for 1968-72. The codes are stamped on the passenger side axle tube and are SUPPOSED to be located on the tube just slightly above the centerline and 3-5" away from the differential case(pumpkin). You may need to use a putty knife or wire brush to remove grease, grime, dirt to see the code. Sometimes the code will be lightly stamped and sometimes not at all. You may need to wet the area with water in order to see the stamping if present.

1968-1970 Ratio----Open----Posi

• 2.56------ LK-------LT
• 2.73------ LL-------LO
• 2.93------ LB-------LW
• 3.23------ LC-------LP
• 3.42------ OH-------OO
• 3.64------ ---------OW
• 3.91------ ---------OZ

1971-2 Ratio----Open----Posi

• 2.56---- LKB---- LTB
• 2.73---- LLB---- LOB
• 3.08---- LAB---- LSB
• 3.42---- LHB---- LWB

Note: For 1972, last character, "B" is missing! When putting in a 71-2 rear axle into earlier models, you will have to shorten the driveshaft approximately 1" to accomodate the larger yoke found on the 1971-2 axles.

Springs for 70 to 72 GS