GM rear gears

[PxTx]

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]

My math says that it is 4.11 :1

[PxTx]

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]

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]

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]

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]

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]

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]

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]

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.

[JoeC]

Pontiac also used some gear ratios that were inbetween the Chevy ratios.

[PxTx]

I received this rear with the housing freshly blasted and painted. All of the internals were included in a box. I'll be assembling the rear soon.

The carrier is a 4 series unit, which is one of the indicators leaving me to beleive that this combination was original. Most people who went from a 3 series gear to a 4 series used a spacer plate, very few spent the extra money for a new 4 series posi unit.

I am pretty sure that a BOP ring gear will not bolt onto a Chevy 12 bolt carrier, the 4.33 I have does.


Cheers,

Paul Tholey

[Casey Marks]

Are you sure that the 4-series posi and related gear are in fact Chevy guts ? As JoeC suggests, BOP had ratios typically in between the Chev's. I don't *believe* that Buick had a 4.33, but Olds and Pontiac did. They may be Olds or Pontiac guts that you got in a box with the Chevy housing ?? Justa thought - especially if you never had the whole thing put together as an assembly.

[PxTx]

The carrier casting numbers check out as a 4 series Chevy 12 bolt posi. I'm not sure how to determine the date of manufacturing thought.

[YENKO DEUCE REGISTRY]

px;
Been to all of the Hatboro shows, lived in Hatboro for 8 years till last Sept. If you've been to that show, then you must have seen the Huggar Orange '69 Yenko Camaro that was there - usually at the end by DaddyPops.

If your R&P is a chevy unit, and you're sure about the 39, count the teeth to make sure it is not mis-stamp.
M

[Casey Marks]

DUH !!! Casey .....

After thinking about it - I'm convinced it was originally in a Pontiac application. The Chev and Pontiacs both had *12-bolts*, as most know them, but the Olds is a *pseudo-12-bolt* in that it has a 12-bolt cover with a 10-bolt ring gear.

That's my final answer ...... http://www.yenko.net/ubb/smilies/images/icons/smile.gif

[PxTx]

Yep, I've seen that Hugger. Where did you move to?

My other sister's 69 Camaro was right at DaddyPops in the 1999 show. It is Midnight Blue with the white stripes (down the smoothed firewall) and has a X-ram in the trunk. Anyways it's amazing we've never talked before. Do you know Mike Clark or Andy Good? I spent a summer during college working next to them. I was working at Shawn Ferrel's "The Vette Shop".

As for the 4.33 gears, Casey's answer is makes perfect sense, although I do find it slightly ironic that both the housing and the ring and pinion have are for 1970 applications. The date code on the housing is before the ring and pinion, for whatever that is worth.

I counted the ring gear teeth and there are 39 of 'em. Since she (my sister who is building the B-M Nova clone) has the 4.33 gear, I think that is what she'll run. After all some comprimises have to be made due to her budget.

Thanks for all of the input guys!

Paul Tholey

[YENKO DEUCE REGISTRY]

Paul;
The HO Y-Camaro is a second owner car, he bought it from a used car lot in December of '69 in Flourtown. Car was orig. from Marshall Chev. in Reading, PA, and is a 4speed with p/s and v/t. The owner has some really cool photos of him racing it at Maple Grove in the '70's.

I have never been to the Vette shop, but have heard about for years. I moved to Douglassville, (out by Collegeville), and am now closer to Maple Grove, the HO Yenko and a Lemans Blue Yenko Camaro in Phoenixville that is also a second owner car believed to have been purchased off of the same used car lot in Flourtown in 1970!
M

[Kurt S]

That axle could also be from a 69 Camaro. They started coding the 3 letter rearend codes in 1970 model year and many of the late 69 Camaros got it.
I believe that gear was available over the counter and the dating kinda confirms that. Several unusual ratios were sold over the counter and never in a production vehicle.

Kurt

[PxTx]

Coupe Chevrolet used to be in Glenside, PA until 1969. They then moved to Flourtown (the next town over). My father knew of Dewan's. He said they had all of the higher end hot cars. It wasn't much of a used car lot- everything was inside- more like a showroom.

As for those 4.33 gears, I just found out that they ARE Chevrolet gears. They are over the counter (Kurt S. you were right!) They were discontinued in 1981. The previous P/N I posted was found on the ring gear. If it would help anyone, the true P/N for the ring and pinion is 3961430.

I must retract the statement I made earlier about the GM 4.11 gears that were for a 3 series carrier. I checked them myself and found out the previous owner of these gears misrepresented them, they are simply 3.73s.

Thanks everyone!

Paul Tholey

[PxTx]

Marlin,

Are you familiar with Coupe Chevrolet? My father started working there in 1970. What was the name of the used car lot that sold the HO Y-Camaro?

As for the OTC gears, I have found a set of GM OTC 4:11 gears for a 3-series carrier dated 1968 (I think).

So the choice now for the clone is which gears to run in the Nova? Anyone know about B-M camshaft options?

[YENKO DEUCE REGISTRY]

pxtx;
I never heard of Coupe Chev. The used car lot in Flourtown that sold the two '69 Yenko Camaros was called Ed Dewan's Performance Cars.
M

[Kurt S]

Just one of those things I remembered looking thru one of my parts manuals. http://www.yenko.net/ubb/smilies/images/icons/smile.gif