To all, thank you for the guidance provided !!!! I purchased a 66 roadster last year and the prior owner indicated that it had a 3.36 geared rear end. I have been ubable to find and stamping indicating this. Is there any identifying marks/codes and where would I find this? It has an L-72 engine. Thanks to all in advance

 

The code is on the right front side of the differential carrier.
3.36 would have code AK,AM or AU, followed by month and day built followed by the Plant which could be B, G or W.

 

Here is a small table of codes for 1965-67 rear end codes.
1967 Corvette Rear Diff Gear Codes

Codes - Non-Locking Codes - Locking Ratio Inspection Cover
AL, AT 3.08 10 Bolt
AK AM, AU 3.36 10 Bolt
AN, AZ 3.55 12 Bolt
AS AO, FA 3.70 12 Bolt
AP, FB 4.11 12 Bolt
FC 4.56 12 Bolt

1966 Corvette Rear Diff Gear Codes
Codes - Non-Locking Codes - Locking Ratio Inspection Cover
AL, AT 3.08 10 Bolt
AK AM, AU 3.36 10 Bolt
AN, AZ 3.55 12 Bolt
AS AO, FA 3.70 12 Bolt
AP, FB 4.11 12 Bolt
FC 4.56 12 Bolt

1965 Corvette Rear Diff Gear Codes

Codes - Non-Locking Codes - Locking Ratio Inspection Cover
AR AL, AT 3.08 10 Bolt
AK AM, AU 3.36 10 Bolt
AN, AZ 3.55 12 Bolt
AS AO, FA 3.70 12 Bolt
AP, FB 4.11 12 Bolt
AQ, FC 4.56 12 Bolt


This is looking from the floor under rear up at the rear end - located where halves are bolted together.

 

would it be possible to get the codes for 64's? thanks

 

Here is 1963-67 codes:
CORVETTE REAR AXLE CODES
All the data entered here is from GM Parts Manuals.
YEAR DESCRIPTION CODE
63 3-Spd 3:36 Ratio CA
63 Positraction 3:08 Ratio - CJ
63 Positraction 3:36 Ratio - CB
63 Positraction 3:55 Ratio - CC
63 Positraction 3:70 Ratio - CD
63 Positraction 4:11 Ratio - CE
63 Positraction 4:56 Ratio - CF
63 4-Speed 3:08 Ratio - CZ
63 4-Speed 3:70 Ratio - CX
64 3-Spd 3:36 Ratio - CA
64 Positraction 3:08 Ratio - CJ
64 Positraction 3:36 Ratio - CB
64 Positraction 3:55 Ratio - CC
64 Positraction 3:70 Ratio - CD
64 Positraction 4:11 Ratio - CE
64 Positraction 4:56 Ratio - CF
64 4-Speed 3:08 Ratio - CZ
64 4-Speed 3:70 Ratio - CX
65 3:36 Ratio - AK
65 Positraction 3:08 Ratio - AL
65 Positraction 3:36 Ratio - AM
65 Positraction 3:55 Ratio - AN
65 Positraction 3:70 Ratio - AO
65 Positraction 4:11 Ratio - AP
65 Positraction 4:56 Ratio - AQ
65 3:08 Ratio - AR
65 4-Speed 3:70 Ratio - AS
65 396 - Positraction 3:08 Ratio - AT
65 396 - Positraction 3:36 Ratio - AU
65 396 - Positraction 3:55 Ratio - AZ
65 Positraction 3:70 Ratio - FA
65 396 - Positraction 4:11 Ratio - FB
65 396 - Positraction 4:56 Ratio - FC
66 3:36 Ratio - AK
66 Positraction 3:08 Ratio - AL
66 Positraction 3:36 Ratio - AM
66 Positraction 3:55 Ratio - AN
66 Positraction 3:70 Ratio - AO
66 Positraction 4:11 Ratio - AP
66 Positraction 3:08 Ratio - AR
66 4-Speed 3:70 Ratio - AS
66 396 - Positraction 3:08 Ratio - AT
66 396 - Positraction 3:36 Ratio - AU
66 396 - Positraction 3:55 Ratio - AZ
66 396 - Positraction 3:70 Ratio - FA
66 396 - Positraction 4:11 Ratio - FB
66 396 - Positraction 4:56 Ratio - FC
67 3:36 Ratio - AK
67 Positraction 3:08 Ratio - AL
67 Positraction 3:36 Ratio - AM
67 Positraction 3:55 Ratio - AN
67 Positraction 3:70 Ratio - AO
67 Positraction 4:11 Ratio - AP
67 4-Speed 3:70 Ratio - AS
67 427 - Positraction 3:08 Ratio - AT
67 427 - Positraction 3:36 Ratio - AU
67 427 - Positraction 3:55 Ratio - AZ
67 427 - Positraction 3:70 Ratio - FA
67 427 - Positraction 4:11 Ratio - FB
67 Positraction 4:56 Ratio - FC

 

thank you VERY much !!

 

This was answered yesterday.

http://forums.corvetteforum.com/c1-a...rmination.html

 

took the time to check my case number; curious as to ratio. i have "CA 5 25 and either CA or GA" can't clearly make out the 2nd to last letter. according to the above chart i have a '63 or '64 3-speed 3:36 rear. the car is a late, (6/64) build with original p.g. i have no way of knowing if the rear was changed at some point, but everything that i can check on the car is original, carb, alternator, master cylinder, engine, etc. what does the 5 and 25 indicate? has anyone else run into a similar situation or know of a 3-speed rear being originally installed in a '64? also, i presume this is NOT a posi? thanks for you help.

 

If you look at the chart provided above by Bobonthis, your rear is from a three speed non posi and should say CA 5 25 64 based on what you say. That would be a 3:36 made on May 25th, 64.
According to Corvette World charts, that same rear axle was used in powerglide rears in 64. I'd say it's either original, or at the very least the numbers match up to the car and build date.
The CB rear was also used in powerglides, but it's a posi.

 

The rear may not be a posi, however a quick way to tell is by jacking rear of car up and chocking front tires, put trans in neutral & turn one of rear wheels. If other side turns in the same direction it is a posi. If it turns in opposite direction it is not a posi.

 

Yep, I know it's a 11 year old thread; however, there's a lot of good info above.

I just checked my rear end and found this code:
1CAM 11 11 69 W

I know it's a posi rear end from jacking up the rear and spinning a wheel, but seems like I have a lot of extra characters like the W suffix. I have a 65 with 4 speed trans.
1 prefix would be "1st shift"?
69 would be the year?

 

Due to the extended production of the 1969 model year (into December 1969), the later cars would receive the 3 character code that was used on all 1970 cars (GM returned to 2 digit codes in 1971). Your CAM translates to a 3:36 posi (in a car with a 350). The 1 preceding it is for the 1st shift and the W indicates the Warren, MI plant. Given the Nov 11 assembly date, most likely it made it into a 69 with an outside chance perhaps a very early 1970.

 

69-71 posi cases were also not the best, BB and SHP included.

 

amazing, thank you!
I spent way more time than I want to admit trying to find that, and you just whipped it out like it was no big deal.

@GTR1999 , what do you mean the cases were not the best? Prone to leaking?
I just found out that previous owners converted my L75 to a L76, and popped in this 3.36. Was hoping it was a 4.11, but oh well.

 

Well first we need to speak the same language. The housing is called the Carrier but most call it the housing or case. The case is the posi case inside the diff. The posi cases used in 69-71 were better than the 63-68's but not the best. The problem was cracking. If you have an unknown diff in the car I would at least check the axle endplay.

 

thanks for that lesson!

 

So I'm a little late to the party but I just bought a 63 corvette convertible from the second owner. He bought the car in 67. He said he changed the rear gears to 4.11 in 69 and promptly blew the engine. He said he replaced the 327 with the current 350 and changed the rear gears to 3.73. The number on the block supports that its a 350. However, the # on the rear carrier is FB12 26 65. According to the table above this is a 65 Posi with 4.11. Now my question is did he lower the gears in the current rear to 3.73

 

You would only know by pulling it out inspecting the numbers on the gear if they were changed. For an estimation, jack up the car and add a piece of tape around the driveshaft - mark it on the bottom. Then have someone spin the tire 1 revolution while counting how many times the drive shaft rotates. if it spins 3 full revolutions and about 3/4 of the way you probably have 3.73s.

 

thank you! I have it on jack stands to get tires so I can try this later today.