GM rear gears

**PxTx** · #1 05-16-2001, 03:27 AM

Thanks to all who contribute to the exciting forum. I thoroughly enjoy reading the posts and enjoy trying to figure out some of the "mysteries" of Chevrolet.

This evening while laying out the differential internals for my little (16 years old) sister's 69 Baldwin Motion clone/tribute/replica... I discovered a ring and pinion that is somewhat mysterious to me.

It reads 2 GM 3936482 9-37 3 70 11

This has a 37 tooth ring gear and a 9 tooth pinion. My math says it is a 4.33 gear. Has anyone ever heard of GM producing such a gear? I would be very interested to hear you input.

FYI: Although she is building a "clone", the car will never be sold in her lifetime. I say this to re-assure those who are concerned with people building clones that are sold as genuine.

bbdon · #2 05-16-2001, 05:40 AM

My math says that it is 4.11 :1

**PxTx** · #3 05-16-2001, 11:02 AM

Yes, the 9-37 would work out to be a 4.11. Now I thought the 37 was a 39 last night. I'll have to double check that, but I think it was a simple mistake.

Does anyone know a site where I can check those GM numbers on the gear? Can anyone suggest a good book for the Nova numbers? I know there are several for the Camaros

TIA

Paul Tholey

**YENKO DEUCE REGISTRY** · #4 05-16-2001, 02:50 PM

Paul,
The Chevrolet by the Numbers books are good sources of info for drivetrain explanations, and for the Nova 'numbers'.

Are you building a BM-Nova clone?

Glenside, PA? I guess you know about the Dusk Blue '69 ZL1 Camaro that was running around there since '69. Heartbeat Jimmy bought it last year, bummer.
M

**PxTx** · #5 05-16-2001, 08:49 PM

There was a type-o in my original post. The ring gear has 39 teeth on it. The ring gear reads:

2 GM 3936482 9-39 3 70 11

Sorry for the confusion.

Yes M, I knew the car. I work with a guy who worked with the previous owner. I actually am in Roslyn right now (with my parents), but I make settlement next month and will be moving 2 miles down the road in Glenside.

Finally, I'll be able to bring my 65 Malibu SS L79 car out of the storage it's been in for the last 7 years. I haven't seen it since high school! Yes, the new house has a garage, but not as big or nice as my fathers I'll be gettin married in October.

The B-M clone is being built by the younger of my two little sisters. The inspiration began when I she bought the frost green Ertil B-M model. She had just rencently purchased a very similar looking 69 Nova. After reading about these cars, she was hooked. The biggest snag was recreating/locating the hood, but thanks to Ed Cunneen that has been resolved.

Her goal is to try and make it appear as correct to the period. She'll want's to attempt to reproduce a window sticker and all that good stuff. Kinda try and recreate for folks the feeling of what it would be like to walk up to one of thses cars at the Baldwin dealership and dream.

My two sisters have a lot of fun at the shows, they dress up in 50's and 60's period clothes and really try and look the part. If anyone has been to either the Glenside or Hatboro PA shows in the past 3 years, they've probably seen them. Sorry for the ramblings guys.

Paul T

**PxTx** · #6 05-17-2001, 12:23 AM

Just got the Axle Code from this rear.

C BT 1013G1
....... E

(just ignore the periods, I used them to try and show the position of the E)

I thought the "E" would have been found at the end of the string, but it is below it. I cannot understand what the "C" designates and the "1" following the "G" is a bit mysterious too.

Between this and the GM 4.33 gear, I'm beginning to thing this may be a true, but undocumented option. Any idea guys?

**COPO** · #7 05-17-2001, 12:57 AM

CBT is a 3.55 12-bolt posi rear from a 1970 Nova. The "E" stand for Eaton and means it is a factory posi. The "1" following the "G" stands for 1st shift. Some cars will have a "2" for 2nd shift. "1013" is the month and day of assembly of the rear. In this case 10 = October. 13 = 13th day.

**PxTx** · #8 05-17-2001, 02:48 AM

Okay, I now understand the shift numbers. I'm glad to see that I got the month and day info correct, but is it safe to assume the C designates a Nova? Or is the C the year?

It turns out that the housing may not be all that exciting, The "C" is what I was hoping was different.

I am still slighly suspicious of this pakage due to the GM 4.33:1 gears which are dated 3-70. If the housing was made in 1970 rather than 1969, it leaved the posibility that it came this way from the factory (I think)

My local GM dealer check the avaiability of the part number (actually called Detroit) of the ring and pinion and it came up that discontinued!

I understand that what I am asking is not intended for a true #'s Supercar and only a clone. Therefore I do not want to wear out my welcome, but I still am intereted in hearing if anyone has ever heard of GM producing a 4.33:1 gear, and if so was it ever factory installed? I know they made one because I'm holding it in my hand, and the part number checked out.

**COPO** · #9 05-17-2001, 11:07 AM

There is nothing unique about the "C" all Chevrolet rear codes started w/a "C" for the 1970 model cars. The rear was assembled on October 13, 1969 for a 1970 Nova and there is a 99.999% probability it came from the factory w/3.55 gears installed and a posi unit.

Casey Marks · #10 05-17-2001, 11:45 AM

Boyz - I am wwwaaaaayyyy outta my league here, but ........

Olds did offer a 4.33 gear set for their "O" axle. This is obviously not the same as a typical Chev 12-bolt or a B-P axle. It is it's own animal and uses it's own internals.

px - do you know if this ring and pinion was in your existing carrier ? If not, it very well could be an Olds unit, ...........

I have a 4.33 Olds R&P stashed away, and will check the numbers on it to see if they match up to what you've got.

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