I recently bought a set of 12 bolt gears off of E-Bay. They were not advertised as GM gears. When I received them, they had the GM stamp with the following information on them:
Pinion-on the head "1Z"-on the stem between the large and small pinion bearing: 339627 10 34 6 74 GM 10 teeth.
Ring gear: 6270998 10:34 GM 67402 and in another area 2-10 34 teeth. Does anybody know if these will work in my 12 bolt car application? I also posted over on the Camaros.net forum as well to see if anyone there can help me.

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1969 Camaro 383/365HP, B/W T-56 Six Speed, 12 bolt, Eaton Posi! 3.73, 4 Whl. Disc brakes, console w/Auto Meter gauge package, tach, clock, tilt wheel, Black Deluxe houndstooth interior, rear window defogger.

Compare the diameter of the pinion shaft next to the head where the large bearing presses on. The car pinion is larger than the truck pinion. If they are the same size then you may have a car gear. I would need a little more information before I could say for sure. The other dimentions are the same for a car and truck 12 bolt.

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'69 RS/SS396 Pro Street
427 4 speed 9"
Byars Performance
High Performance Drivetrain Parts & Service
www.lubedealer.com/biggearhead (http://www.lubedealer.com/biggearhead)

[This message has been edited by big gear head (edited 08-28-2002).]

The diameter on the truck gear pinion is 1.438 and the pass car is 1.625.

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1969 El Camino
69 LS1 335 HP 427
( not the origional engine)
M21 12 Bolt 3:07's.
Daily Driver work truck.

None of my GM parts books show a 3.40 gear for the 12-Bolt passenger car rear. 2.29, 2.56, 2.73, 3.07, 3.31, 3.55, 3.73, 4.10, 4.56, 4.88 and 5.13 are the ratio's from GM. . . . .that I know of!

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Dave
My 65 El Camino (http://home.attbi.com/~bates150/images/dad/elky4.jpg)
Tri Power #1 (http://home.attbi.com/~bates150/images/dad/tp_left.jpg),Tri Power #2 (http://home.attbi.com/~bates150/images/dad/tp_right.jpg)
New Richmond 5-Speed (http://home.attbi.com/~bates150/images/dad/rod5.jpg)
Fan/Shroud/PRC Radiator (http://home.attbi.com/~bates150/images/dad/fan_and_shroud1.jpg)
M22, 3.73's

3.40 was a truck ratio. They also had 3.21 & 3.73 in the 3-series truck diffs.