Hello. I found this information when trying to determine which gears / diff were in my 72 skylark. Thought I'd share it here for any others that may be curious . Rear Axle Tips And Decoding by George Nenadovich Most Skylark/GS cars from 1968-72 have open (non-posi) rear axles. From 1968 to 1970, rear axles were 8.25" and and afterwards were 8.5" coporate rear axles. The 8.5" is the most common rear axle and is still in use today in GM rear wheel drive cars and trucks. The most common gears found in Skylark/GS cars are 2.56 and 2.73 ratios. Typically, 2.56 is found in 350-2bbl cars with and without ac. The 2.73 ratios are found in cars with 4 bbl set-ups and most Skylark Custom cars which usually are 4 bbl cars. GS cars do NOT have posi rears! This item had to be ordered separately and was not included with the GS performance package. GS cars did get the higher ratio 3.08 as standard from 1970-72. GS cars did NOT come with 12 bolt Chevy rear axles unless they were made in Canada or for Canada. Even then, they are not posi axles. The easiest way to determine if a car is a Canadian model is to look at the trim tag attached to the top of the firewall and in front of the cowl-to-hood seal. In 3/8" high characters, the first line of text will state "MADE IN CANADA." All A-body rear axles will interchange. From 1965 to 1972, the rear axles are bascially the same except for the different size ring gears stated above and the 1965-7 axles being one inch narrower. A-bodies are considered to be Lemans, Skylark, Chevelle, Cutlass and from 1970-2 Pontiac Grand Prix and Chevy Monte Carlo. If you install a 12 bolt rear axle, you will need Neapco #3-3130 rear u-joint since the Chevrolet yoke is different from the Buick, Olds, Pontiac axles. Also, when putting in a 71-2 rear axle into earlier models, you will have to shorten the driveshaft approximately 1.5" to accomodate the larger yoke found on the 1971-2 axles. Axles for A-bodies are grouped into years as follows: 1965-67 1968-72 1973-7 1978-87 Axles in the above groups do not interchange except as stated above. 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 Code 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! This information was found on the website : http://www.buickperformanceclub.com/axles.htm I hope this information is helpful , sure helped me. Chris
