calculate rear axle ratio

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pagilman

pagilman

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:study:I just turned my rear wheel 10 times, while counting the driveshaft weight @ 16 times. I think I was supposed to count the drive shaft yokes, that would have given me 32 revolutions. which I think would be 3.23 gears. Do you guys agree or did I do it wrong? thanks Walt:coffee2:
 
turn the wheel 1 revolution and count the revolutions of the driveshaft...on a posi it(driveshaft) will turn about 3 and a quarter times for a 323
 
pagilman said:
:study:I just turned my rear wheel 10 times, while counting the driveshaft weight @ 16 times. I think I was supposed to count the drive shaft yokes, that would have given me 32 revolutions. which I think would be 3.23 gears. Do you guys agree or did I do it wrong? thanks Walt:coffee2:
Click to expand...

Woh, i don't know, you lost me. Why not just turn the drive shaft and see how many turns the wheels do. 3 1/4 turns would be 3.23...or is it the other way around...whatever, where did you hear to turn the wheels 10 times?
 
terzmo said:
turn the wheel 1 revolution and count the revolutions of the driveshaft...on a posi it(driveshaft) will turn about 3 and a quarter times for a 323
Click to expand...

I thought that also, tryed it , it doesn't work. One turn of the wheel will give you about 1 1/3 revolutions on the drive shaft.
 
Like said above, take a marker and mark the side or the tire and the Driveshaft. Then start turning the driveshaft w/ the car in neutrel and rear wheels off the ground. Then count how many times the driveshafts turn to make the tire go 1 revolution. If it turn a little over three times then it's a 3.23, not 3 whole turns 2.73, little over 4 turns 4.10, and so on and so forth.
 
Wow! Never heard of doing it that way Walt and to be honest you totally lost me. Here's how you do it.

Jack both drive wheels off the ground. Put a mark on the driveshaft and one on a tire for reference.

If it's a sure grip rearend turn the wheels exactly one revolution and count how many times the driveshaft turns. If it turns slightly over 4 turns it's a 4:10 ratio. If it turns 3-1/2 times it's a 3.55 ratio, if it turns 2-3/4 times it's a 2.76 ratio, etc.

If it's not a sure grip, in other words it's an open differential, block one wheel from turning then turn the other exactly one revolution while counting the revolutions of the driveshaft. Multiply the revolutions of the driveshaft by 2 and that's your ratio. In other words if the driveshaft turns slightly over 2 turns it's a 4:10 ratio. If it turns 1-3/4 times it's a 3.55 ratio. If it turns 1-5/8 times it's a 3.23 ratio, etc.
 
fishy68 said:
it's an open differential, block one wheel from turning then turn the other exactly one revolution while counting the revolutions of the driveshaft. Multiply the revolutions of the driveshaft by 2 and that's your ratio. In other words if the driveshaft turns slightly over 2 turns it's a 4:10 ratio. If it turns 1-3/4 times it's a 3.55 ratio. If it turns 1-5/8 times it's a 3.23 ratio, etc.
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It's more accurate to turn the one wheel TWO turns, and just count the driveshaft
 
pagilman said:
I thought that also, tryed it , it doesn't work. One turn of the wheel will give you about 1 1/3 revolutions on the drive shaft.
Click to expand...

As I said, you evidently have a "open" differential (not a sure grip)

Simply turn the wheel TWO turns and count the shaft.

If you properly counted FULL TURNS (full revolutions) when you turned the wheel 10 times, the shaft should have turned 1/2 of 32.3, or just over 16

Since you seem to have an open rear, you could have turned the ONE wheel TWENTY revs, and the shaft would turn 32.3 turns.
 
If you want accurate, count the number of teeth on the ring gear, then count teeth on pinion. Divide the number of pinion teeth into the number of ring gear teeth and you have your ratio.

Example: 45 ring gear divided by 11 pinion equals 4.10
 
67Dart273 said:
As I said, you evidently have a "open" differential (not a sure grip)

Simply turn the wheel TWO turns and count the shaft.

If you properly counted FULL TURNS (full revolutions) when you turned the wheel 10 times, the shaft should have turned 1/2 of 32.3, or just over 16

Since you seem to have an open rear, you could have turned the ONE wheel TWENTY revs, and the shaft would turn 32.3 turns.
Click to expand...

I jacked only the drive wheel up. turned the wheel 10 revs and counted 16 revs of the shaft. I am reasonABLY ASSURED THAT i HAVE a 3.23. Thanks to all, the rear is coming out a 3.91 sg is going in soon.:cheers:
 
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