How to decipher dates on a ring an pinion.

[Richard G.]

have a 1963 SWC. Dec 21 born date.
I just pulled my differential apart and cleaned up the parts.
It appears the gears have a 1965 GM Date on them.
11 65 9 32
Part number 3820899

They are also 3:55 gears, which is not standard as I have a 340HP 4 speed Car.
But many have been an option.
I have posted a couple pictures.
The differential is stamped CE1212 62
Casting date of K82
Casting # 3818758

Just wanted to confirm what I am reading as dates on the gear set is really that.
If it is it would appear the differential was repaired fairly early in its life.
Thanks
Rick

[Mike E.]

Re: How to decipher dates on a ring an pinion.

You are right on. 11 65 is November 1965. 9 32 is 9 teeth on the pinion, 32 on the ring gear. Divide 32 by 9 and you get 3.55.

[Mark M.]

Re: How to decipher dates on a ring an pinion.

Hey Richard, It appears the numbers you show for the gear is correct for 63-64 3:55. That gear set was needed to go with the coarse spline on the front yoke. In 65 the yoke changed to fine. That gear set was available from gm at least into the 1980's . The CE1212 62 stamp on your case would be for a 4:11 gear dec. 12 1962. I would have to double check but the 63-64 dana posi carriers, I believe are like the 65-69,mid 69-79 eaton carriers where there are two sizes, 4 series -4:56,4:11 carrier and 3 series 3:70-3:08. To use 3:55 they would have to change the carrier too. If they did the stronger eaton would be better. I didn't see the pictures. The 3818753 is correct 63- early 65. The cast date seems right on. 4:11 was available with 340 hp and if the car came that way and it's an early 63, it would have a close ratio T10. Are you looking to put back to 4:11? My favorite all around street gear is the 3:55, for this type car. Happy wrenching Mark

[Richard G.]

Re: How to decipher dates on a ring an pinion.

Mark;
Thanks for checking on this for me. Stock un-optioned would have been 3:73. Interesting the car came with 4:11, this is the first time I have had the information from the stamp deciphered. It was under a lot of goo till yesterday! Somewhat explains the change in ratio. The carrier is, of course, the 3 series with the 3:55 gears. I plan on keeping it this way. Years ago I did a extended road trip and got 18mph on the highway. NCRS will not check the installed ratio against the tag so I am good. I believe it's a Borg Warner carrier. Correct close ratio T10 is also there.
Thanks
Rick

Hey Richard, It appears the numbers you show for the gear is correct for 63-64 3:55. That gear set was needed to go with the coarse spline on the front yoke. In 65 the yoke changed to fine. That gear set was available from gm at least into the 1980's . The CE1212 62 stamp on your case would be for a 4:11 gear dec. 12 1962. I would have to double check but the 63-64 dana posi carriers, I believe are like the 65-69,mid 69-79 eaton carriers where there are two sizes, 4 series -4:56,4:11 carrier and 3 series 3:70-3:08. To use 3:55 they would have to change the carrier too. If they did the stronger eaton would be better. I didn't see the pictures. The 3818753 is correct 63- early 65. The cast date seems right on. 4:11 was available with 340 hp and if the car came that way and it's an early 63, it would have a close ratio T10. Are you looking to put back to 4:11? My favorite all around street gear is the 3:55, for this type car. Happy wrenching Mark

[Richard G.]

Re: How to decipher dates on a ring an pinion.

Well is interesting what one finds when you get deep into an old Corvette.
Most were road hard and put away wet, this one is no exception.
At least is seems the change was reasonable, 4;11 to 3;55 is a good move.
Interesting their is only 9 day between the differential build and the car build dates.
I had always assumed the Corvette had the stock 3;70's in it.
"Well I was wrong" and it wasn't the OEM ratio either.
Just don't tell my wife I said that!
Rick