Rear Differential Case ID Question

[John R Taylor]

Hi! Guys, I have searched the archives...I usually find the answer there, but not tonite. I Have a rear end Carrier # 3889148 at the input snout, with a date code L__4 at drivers output ( no numbers in the middle). Rear Diff. Cover # 3871375, and on the bottom of carrier , in front of bracket for toe bars/ track bars are the letters AWW 346 E1. Can you tell me what year this rearend is? What Gear ratio? (assuming it is same after all these years ) It is installed in a Road racer I bought over 15 years ago. There is a pretty good mix of parts in this one car and I don't know all the things I used to...or used to claim to. Just one other question ...was the rear differential for the Mid-years 65 to 67 Different from small block to Big Block. Such as bearings, thicker case, stronger yokes, pinion shafts, and rearcover/mount? I'm thinking of setting a Big Block back in the hole, and I needed to know what I might I have....I just can't sleep .... wondering about it. Your help is always appreciated, John

[John H.]

Re: Rear Differential Case ID Question

John -

The 3889143 (not 148) carrier casting was used for all '67-'75 diffs, and the partial casting date indicates a December, 1974 casting. The code stamping indicates a 3.08 Positraction, assembled in mid-December, 1974, for a 1975 Corvette. The only difference between a BB and SB diff is the output yokes - bolted caps for BB, U-bolts for SB (all 75's were small-blocks).

[John R Taylor]

Re: Rear Differential Case ID Question

John Hinckley, Thanks for the info. I looked at the output yokes...There are heavy metal bolted caps. That snout part number is clean, and the third number Has a lump at the top of what appeared to be an 8 , I can't really tell, and the last number looks like a fully formed 8...but if no such part exists ...I bet you are right it's a 3. If I attached a photo closeup..would you take a look or did the AWW 346 E1 confirm its date of production? John T

[John H.]

Re: Rear Differential Case ID Question

John -

The "L_4" December '74 casting date and the 346th day on the stamp pretty much nail the production date at Chevrolet-Warren as first shift, December 13, 1974. The previous diff casting numbers used in 1966 and prior aren't even similar to the 3899143.