question about ring and pinion - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**nightmare** · 10-22-2003, 02:27 PM

i recently purchased a used ring and pinion. i was told that this was a stock 3.42 for a GM 12 bolt rear. although, i count the teeth on the ring, 34, and the pinion, 10, it calculates to a 3.40. does that sound right?

also, the numbers on the ring are in between the teeth, so some of them are cut off. here is what i can read:
9 10: GM 783 (with the spaces being where the empty part of the teeth are)

here are the numbers on the pinion:
339627
10 37 10 78

could someone help me out and let me know what i've purchased? thanks in advance

woodmancfh · 10-22-2003, 08:30 PM

I would say that if there is 34 teeth on the ring gear and 10 teeth
on the pinion gear it is definitly a 3.40 gear ratio. Your doing your
math right. To get a gear ratio just divide the number of teeth on
the ring gear by the number of teeth on the pinion gear.

Vince M · 10-22-2003, 09:03 PM

You didn't say that the application was for a truck or not. The correct ring and pinion count for a 3.42:1 ratio should be 41 and 12. They just round the number to 3.42. None of them seem to come out exactly. (Although yours does).

Check out DriveTrain.com

Lots of good info....

**kwmech** · 10-22-2003, 09:29 PM

Definately count the teeth on the gears and divide by those numbers it may be 3.70 GM 783 is the match number------339627 is the part number 10 78 is the date of manuf. 10 37 may be the ratio.

**nightmare** · 10-22-2003, 10:41 PM

i should have said whether it was for a car or truck. the guy told me that it was for a truck

10-22-2003, 08:30 PM	#2
woodmancfh GMC RULES Join Date: Feb 2001 Location: Central Ohio Posts: 154	I would say that if there is 34 teeth on the ring gear and 10 teeth on the pinion gear it is definitly a 3.40 gear ratio. Your doing your math right. To get a gear ratio just divide the number of teeth on the ring gear by the number of teeth on the pinion gear. __________________ 70 Chevy C/20 72 GMC K /2500

10-22-2003, 09:03 PM	#3
Vince M Senior Member Join Date: Apr 2000 Location: Orlando, FL Posts: 1,076	You didn't say that the application was for a truck or not. The correct ring and pinion count for a 3.42:1 ratio should be 41 and 12. They just round the number to 3.42. None of them seem to come out exactly. (Although yours does). Check out DriveTrain.com Lots of good info.... __________________ ............................................................ 68 Chevy CST SWB w/LS1, carb & 700r4. Golden Anniversary clone with a few improvements.

10-22-2003, 09:29 PM	#4
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,450	Definately count the teeth on the gears and divide by those numbers it may be 3.70 GM 783 is the match number------339627 is the part number 10 78 is the date of manuf. 10 37 may be the ratio.



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