I am trying to read what's left of my tank sticker. Luckily the upper left quarter with all of the important stuff (L36,C60,etc.) is very readable. Here's what I need help with: I have G81 in the upper portion which is Positraction axle, but anything to the right of the word axle is missing. Now I go to the optoin list and on the right I can read TIO very plain. I think it is the end of ratio. The "O" is directly above the "H" in wheel (two line items down). I figure that is tilt-telescopic steering wheel. The left column where the RPO is listed reads 02G***A. The rest is missing....... What I have is the correct carrier housing (date) with code AW but the actual ratio is 3.55:1. ????? :confused:


[Modified by silvervetteman, 11:06 AM 4/27/2002]

 

SVM, maybe already know this, but code "AW" is for 3.08:1 axle ratio. For your car, 69 427/390 (either M20 or THM), the standard rear axle was positraction 3.08:1. Positraction was required for the big blocks.

If the car was ordered WITHOUT AC, three optional "performance" axle ratios were available depending on the transmission: 3.36:1 (M20). 3.55:1 (M21), and 3.70:1 (M21). Note that if the car was ordered WITH air conditioning, no performance axle ratios were available; you got 3.08:1. Another interesting factoid is that air conditioning was also not available with the M21 transmission.

There is little doubt in my mind that your differential is the original; finding correct dates is not that easy. It is quite possible that a previous owner may have had the "opportunity" to change the differential gears, and decided to opt for more performance and less gas mileage. The M20 transmission and the 3.55:1 axle ratio did not come from the factory.

I don't have a lot of tank sticker experience, but I expect your tank sticker originally showed the differential as positraction, but if the 3.08:1 was the standard axle ratio for your car, I doubt there would be anything on the tank sticker identifying the axle ratio. What makes you think you have a 3.55:1 axle ratio? Have you counted tire/driveshaft revolutions?


[Modified by Chuck Sangerhausen, 6:11 PM 4/27/2002]

 

Thanks Chuck... I do have factory A/C and that is on the sticker and ...Yes, I have counted the driveshaft revs per 1 wheel rev. 3 1/2 to 1 and varified this when I replaced the side yokes. I am not positive but I do not think the carrier was out before I did the yokes . Also my speedo is correct for 3.55's. I also cannot understand why there would be a number in the options portion of the sticker if I had the standard rear ratio. that's why I am so curious. Most of my car is very original and un-molested. I do not know a lot of the cars history but I have varified a lot of original stuff. I even have the origianal fuel pump, carb, vacuum advance, etc. All of the vacuum lines have the glass tape on the tee's and fittings. (frayed over the years) :confused:

 

Oops. This is what I meant to say, SVM.

In my mind, there are only two possibilities: (1) the axle ratio was changed by a skilled previous owner or he had it changed by professionally, or (2) a mistake was made at the differential factory with the housing being stamped "AW" erroneously. If (1) occurred early enough in the life of the car, and the individual making the change was highly skilled and particular about his work, you would not be able to see any evidence of such change now.

Of these two, I consider the first the more likely scenario; I am sure JohnZ will confirm that mistakes like (2) did happen at the plants, but statistically speaking, I would bet it was low enough as to be insignificant considering the amount of product those guys put out.



[Modified by Chuck Sangerhausen, 7:07 PM 4/27/2002]

 

Thanks chuck... I am trying to enhance the tank sticker so Maybe I can read the option number..I wonder if there are any pro's out there that know some tricks for enhancing photo's that are old and ugly. :rolleyes:

 

Mystery solved!!! I very carefully brushed(with a soft toothbrush) some of the dirt and crud off of the tank sticker and with the help of a photo shop enhancement was able to read the option code 02G92AA... that is 3.08 as you suspected. So .... thanks for the help chuck. You're alright.... I don't care what others say :lol: :lol: :jester :jester :D

 

Holey Schmoley! One hour turnaround on photo shop enhancement including travel and post typing time...you must live next door to the photo shop. :D :D :D

Congratulations on deciphering the puzzle, and thanks for feedback on your findings. It's these little happy occasions that make restoring an old car a lot of fun. :D

 

I have photo software (JASC free trial), so I only had to walk to the computer. It has a million things you can do to a picture or document, so I figured I'd play around with it and try a few things. I can se how fraudulent documents could EASILY be made. Kinda scary!! :eek:


[Modified by silvervetteman, 5:24 AM 4/28/2002]

 

Positraction cars got two different codes, for material and production control scheduling reasons (a computer thing); G81 just meant Positraction, to delete the "open" diff parts from the Bill of Material for that car, then each different Positraction ratio carried its own unique "G" code number to add those specific ratio-related parts back in for that particular car, along with a 2-digit exception letter code after it which selected detail parts to go along with it depending on what other options it was combined with (like speedo gears, where the same Positraction unit required unique speedo gear configuration/part numbers depending on whether it was combined with a Muncie (small speedo gears) or a THM-400 (big speedo gears).

As the computer systems used for Engineering releasing, material control, production scheduling, and cost tracking matured, they became more complex, and "scheduling codes" had to be assigned to many groups of parts that previously were just "standard" and carried no codes in the past, but needed an identifier now that the computers could understand and translate into part numbers - like the "ZQ3" scheduling code applied to the base engine starting in 1969.