My '71 LT-1 has a rear diff that I'm trying to figure out what exactly it is. The bottom pad reads; "W 23 7 1" with no 3 letter code or anything. There's space between the 7 and 1(about 3/4 of an inch)and I can't see any of the other castings until I drop the spring. The stampings I do have are quite clear, and there's hardly any room on the pad for any 3 letter rearend code as the numbers I do have are scattered. Anybody seen anything like this before?
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Re: C3 - 1971 Rear Diff. Decoding
Hey Jeremy, I do believe the two letter code precedes the "W" that identifies the gear ratio.
Robert
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Re: C3 - 1971 Rear Diff. Decoding
For some reasoning, which I don't know, GM actually went back to two letters for the axle ratio designation in 71 after using the three letters in 70.
Your stamp format is completely different from my 70; my differential is stamped 1 CAM 7 24 70 W. About the only part of your stamp that I can read is W (Warren Gear). If the format also changed in 71, the date MAY be 23rd week, 1971 or June 6-12, 1971. Compare that with your car's build date and see it that makes sense in the context. I can't tell you why the ratio designation is apparently missing; maybe someone else knows the answer.Comment
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Re: C3 - 1971 Rear Diff. Decoding
The '71-'72's used a 2 letter ratio code, different from the '70's. However, my '71 has NO ratio code, nor is there room for 2 letters as the "W" is way to the drivers side of the bottom of the case, right where the 2 letter ratio code SHOULD be. I'm missing the ratio code, and either the axle plant OR the Posi plant, which could be either Warren Motive OR Warner Gear. If the numbers 237 DO correlate to the Julian date of the rearend, ASSUMING it was actually cast the 237th day of '70, 1st shift, it would be August 25 or so...and my car build is November '70. 1971 production started in August, and there were no cars built in October '70 due to a strike, so numbers-wise, the diff is plausible. But it SUCKS not having any ratio codes! I was just wondering if anyone else with either a LATE '70 or an early '71 has a rear diff that's stamped goofy.Comment
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What's the carrier casting date ?
Driver side, below and slightly forward of output yoke; and just above the rear strut bracket. Maybe this will help the forensics.Comment
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Re: What's the carrier casting date ?
There's the shift "clock", "H 11 0" ....is that August 11 '70?Comment
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Yes, so it sounds like an orginal unit
August carrier cast to November car is an acceptable spread. Now only to figure out the stamping. Could the "W" you see on the extreme driver side of the bottom flange actually be "AW" (ie. 3.08 ratio)? I've seen some with the ratio code so far to the left that the first letter almost missed the carrier.Comment
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Re: Yes, so it sounds like an orginal unit
I took a REAL good look at it a few min's ago....the "W" is definitely on its own, BUT....RIGHT ON THE EDGE of the left side of the "pad", it's either my imagination or there's a REALLY FAINT glimpse of the tops of what COULD be letters...one of them could be round, like a "D" or a "B"....I don't know, it's a long shot, but it really does look like if it was ever stamped and those really are the tops of letters, the guy doing the stamping must have had some bad acid, because he barely hit the carrier pad. I dunno, a '71 LT-1 with 3:08's sounds a bit odd...whoever ordered this car wanted to go fast as there's no power anything on it. I'd think that it would at least have 3:70's in it(AB). I'm just soaking the bottom of the pad with PB Blaster and scrubbing it with a brass wire brush to knock off the scale....I actually got some decent pics as well. The casting date is nice and bold, although filthy...I guess the only way to know for sure is to either drop the tank and pray the tank sticker is still on the car, or split the carrier and see what gears are in it. And, it is a "Heavy Duty" diff. Thanks for the casting date idea/info....common sense, but I didn't even think to look for that....DUH!!Comment
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Re: Yes, so it sounds like an orginal unit
My 71 - built DEC 14,70 - has the LR W 336 1 (3:36, Warner Gear, DEC @, 70, Ist shift) code. The LR is readible. The housing is dated H 70. I forget the day. Alot of my parts are date coded Aug-Sep. I contribute that to a nine week strike.
ChasmanComment
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Re: Yes, so it sounds like an orginal unit
I'm gonna keep brushing away at it and see if anything comes up...maybe the stampings are buried under all the scale. I just want to try to verify the rear end being original, because I know the leaf spring, shocks, etc. were all replaced A LONG time ago....I'm hoping the diff wasn't as well. So far, looks as if I have a real, yet confusing, original diff, which makes me happy.Comment
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