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Discussion Starter #1
My car is a mutt, originally a I6, swapped to a 350 sometime with a powerglide. With the powerglide the poor little nova couldnt reach 70mph without redlining. (The tires are 235/60R14, btw)

The powerglide eventually gave up the ghost, so we put in a freebie 700r4 to counteract the rear end.

So I have the car up and I'm trying to figure out why the damn rear ratio seems so high. The code is JC G245 2. 10 bolts on the back with the square lugs. On the front of the carrier, on the left between the fins it says "N" on top of "1235542" and on the other side it says "GM I"

So I go to the axle ID page and it seems like JC = 3.08 open. Well, that doesnt seem right, 3.08 isnt that high... So I look and I see the JC code is from 72 to 74, in those cars, if it had a 4 speed, then it was a 3:42 (which would seem closer).

The only thing I can guess is that its the original axle and somebody swapped out the gears, or this rear end might have come from a 4 speed car.
My question is, is there any way to figure out what the ratio of the rear end without opening it up and counting the teeth?
What other rear end fit aside from 67-69 camaros?

Thanks,
Phil
 

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1974 chevy. Ova
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if it's a posi rear, jack it up, count the driveshaft rotations it takes to make the tires turn one full rotation. 4 1/2 times=4.56 gears, etc. if it's an open differential jack up one side and leave the other planted, do the same thing.

the other way is less work...take the car for a drive and write down your RPM's at speed. if the speedo is off (and i'm assuming it is) have a friend set the pace in another vehicle. record the speed. there's a thousand RPM/MPH/Tire size calculators available online. I think www.richmondgear.com has one on their site, and it would be pretty reliable. just remember that you need to know all your other information to figure the gear ratio, like tire size, transmission drive ratio (i think it's .74:1 in OD, 1:1 in 3rd) and engine RPM. if you have a stock converter you can leave slippage at 0 or use a small percentage. i also have 235-60-14's and they're about 25.5" tall.
 

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sproosemoose said:
if it's a posi rear, jack it up, count the driveshaft rotations it takes to make the tires turn one full rotation. 4 1/2 times=4.56 gears, etc. if it's an open differential jack up one side and leave the other planted, do the same thing.
You actually need to rotate the driveshaft enough to get two turns of the wheels, either one turn from each wheel (posi) or two turns of one wheel (open).
 

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Are you sure the transmission is shifting or it isn't slipping?
 

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Discussion Starter #5
The car has been fine since the 700R4 was put in. It shifts good and it counteracts the high rear ratio as it should - its good on the highway, etc.

It was when the powerglide was in that the car wouldnt go over 70.

I just was curious what the ratio was in case I wanted to switch stuff around later on.

-Phil
 
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