Positraction or Not? (LR code)
Thread Starter
7th Gear
Joined: Aug 2019
Posts: 7
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Positraction or Not? (LR code)
Early 1970's rear end codes include AX and LR for a 3.36 ratio, but have never heard why two codes exist for the same ratio. I've also read that both AX and LR codes are Positraction. Anyway, I'm considering buying a C2 1966 L72 vehicle with later-date C3 stamped rear end "LR W 239 1". I suspect it doesn't have Positraction because it doesn't contain an "E" or other Positraction source identifier before between the date (239) and the shift number (1). Then again, in 1975 I believe they dropped the E or other source identifier.
I would appreciate information about the LR code rear, please, so I can make an informed decision. Thanks.
I would appreciate information about the LR code rear, please, so I can make an informed decision. Thanks.
Race Director
Joined: Oct 2000
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From: Shamong, NJ
Positraction became standard in 1970, so any rear dated after 69, is going to be Posi.
AX and LR were both codes for 3:36 rears in 71-75 Corvettes, and LR was also used for 76-77 3:36's. I'm not sure why there are two different codes for 3:36, but it's not Posi verse open. This is just a guess, but it might have something to do with the side axles? Big blocks and LT-1's came with side axles that used bolts and malleable caps, while based motors had side axles with U bolts.
AX and LR were both codes for 3:36 rears in 71-75 Corvettes, and LR was also used for 76-77 3:36's. I'm not sure why there are two different codes for 3:36, but it's not Posi verse open. This is just a guess, but it might have something to do with the side axles? Big blocks and LT-1's came with side axles that used bolts and malleable caps, while based motors had side axles with U bolts.
Thread Starter
7th Gear
Joined: Aug 2019
Posts: 7
Likes: 1
Thank you for your response and explanation. My concern had been based on my reading of “Corvettes By The Numbers, 1955-82”, by Alan Colvin, in which it’s stated that 71-74 stamps included either an E for Eaton positraction, or (-) for no positraction, leading me to believe that “no positraction” was an option. However, that doesn’t seem likely given the benefits of positraction. Thanks again!
