71 LT1 Rear Differential Decoding

[Last84]

All,

I'm considering purchasing a numbers matching 71 LT1. Three quick questions:

1) Did the 71 LT1 come with just a few rear axle gearing combos, or did it come with the full range (3.08, 3.36, 3.55, 3.70, 4.11, and 4.56)?

2) I'm trying to decode the rear differential code. I only have a partial - the mechanic is taking a picture for me. It starts out AW (posi 3.08) and has 343 2 for the fourth thru seventh digits. My books tell me this means it was made by the second shift on the 343rd day of 1971. My mechanic, however, believes this means it was made in 1972 and doesn't match the rest of the car. AW, by the way, was only used in 1971 (CAW in 1970 and not used at all in 1972). Does anyone have any insight into this?

3) Was "2" a standard shift code for the differential? My books just have 1 (first shift), D (day shift), and N (night shift). Anyone know if 2 is valid.

Thanks for any help.
Mark

 

[tomtom72]

Hi & welcome Last84, The following is from 70-72 NCRS Judging Manual I just got in May 04."For 71 &72 the stamping begins with two letters for the ratio code, a letter for the axel plant, one to three numbers for the Julian day of the year*, aletter for the positraction source, and a number for the shift." The astric is for NCRS's explaination of the dating system. I quote, "For the 1971 model year the date code starts with the first day of the calander year 1970 and continues through the 1971 calander year. January = oo1 thru o31." I have found in print that the LT-1's came std with 3.70:1, with 4.11 & 3.55 as optional for all three years, I just can't remember where I found that info.! Sorry. Also the NCRS manual lists for 71 ratio codes AA = 3.55 AB = 3.70 AC = 4.11 AD =4.56 AW = 3.08 AX = 3.36 LR = 3.36 Just for info the 1970 rear end production codes are different. "The production code for 1970 consists of a number(for thr shift that produced the unit), three letters that are the ratio code, the date produced(month 1-12/day/year), and a suffix letter for the plant that produced the differential." Sorry it is not more but I'm sure someone else with more resources will see this thread. tt72

 

[Last84]

TT72 -

Thanks much - I appreciate the info.

Mark

 

[tomtom72]

Hi Mark, You're welcome and no problem. I got the books cause I'm looking at that early C3 period to get back into the hobby so anything I can look up I would be glad to do! tt72

 

[Last84]

Tom,

Thanks again. The mechanic has only given me a partial off the differential - AW and 343 2. I'm hoping that he missed an additional A in front of the AW. I'm pretty sure AA W 343 2 would mean a 3.55:1 differential built by Warner in Michigan on the 343rd day in 1971 by the second shift. If it was made in the Warner plant, there should probably be another W on the end showing it was a Warner Motive Positraction Carrier. Does all this match your info?

I'm also pushing the mechanic to send me a picture - trying to interpret what he's seeing is pretty difficult (and he's supposed to be a NCRS inspector - yikes! - he thinks the 2 after 343 means it was made in 1972).

Mark

 

[tomtom72]

Hi Mark, As far as I can understand the NCRS Judgeing Manual explaination yes I agree with you're acessment on reading the codes. I sympathize with you on the not being there aspect of these transactions. It can be full of second guessing, and with the 70 & 71s it is not cut and dry like the 72s. I don't mean to insult, but you went thru the usual stuff: Tach, fuel line, TI dist #, Carb #, block casting #, Heads and intake and exhaust casting #s, trim tag info, HD drive & half-shafts and u-joints ???? Usually on clones I here the tach is often overlooked, that and I found one with an expansion tank!! Anyway, good luck with the puzzle! tt72 Oh btw, I answered your other thread with some useful info on the stuff I just listed.