Brain failure: computing axle ratio????
Thread Starter
Burning Brakes
Joined: Dec 2005
Posts: 998
Likes: 2
Brain failure: computing axle ratio????
I have flat out thought about this WAY too much.
If you've got the car on a lift, and you turn the wheels, thusly turning the drive shaft, does that correctly correspond with engine revolutions?
I've always thought that it did, but then I made the mistake of thinking "transmission".
SO: if the tranny is in neutral, and you spin the tires one complete circle, and the driveshaft rotates four and a tiny bit, that would be a 4.11 correct? Or does the drive shaft change ratio in any manner coming through the tranny from the engine while in neutral? This is driving me nuts.
I've always thought for 30 years this was an appropriate way to do it but then a friend said "tranny" and now I'm going out of my mind pondering it. Thanks.
I hate thinking.......
If you've got the car on a lift, and you turn the wheels, thusly turning the drive shaft, does that correctly correspond with engine revolutions?
I've always thought that it did, but then I made the mistake of thinking "transmission".
SO: if the tranny is in neutral, and you spin the tires one complete circle, and the driveshaft rotates four and a tiny bit, that would be a 4.11 correct? Or does the drive shaft change ratio in any manner coming through the tranny from the engine while in neutral? This is driving me nuts.
I've always thought for 30 years this was an appropriate way to do it but then a friend said "tranny" and now I'm going out of my mind pondering it. Thanks.
I hate thinking.......
Thread Starter
Burning Brakes
Joined: Dec 2005
Posts: 998
Likes: 2
Originally Posted by 67L36Driver
Your friend is a brick short of a full load. 
That's what I thought. I've always been told (for 30 years) that was the best way to determine the axle ratio cause somebody could have changed the gears inside the housing making the housing stamp # incorrect.
Whew, at least I'll sleep tonight....Thanks.....
Plus the fact that now I know I'm NOT COMPLETELY out of my mind.
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
Originally Posted by Formula Outlaw
I have flat out thought about this WAY too much.
If you've got the car on a lift, and you turn the wheels, thusly turning the drive shaft, does that correctly correspond with engine revolutions?
I've always thought that it did, but then I made the mistake of thinking "transmission".
SO: if the tranny is in neutral, and you spin the tires one complete circle, and the driveshaft rotates four and a tiny bit, that would be a 4.11 correct? Or does the drive shaft change ratio in any manner coming through the tranny from the engine while in neutral? This is driving me nuts.
I've always thought for 30 years this was an appropriate way to do it but then a friend said "tranny" and now I'm going out of my mind pondering it. Thanks.
I hate thinking.......
If you've got the car on a lift, and you turn the wheels, thusly turning the drive shaft, does that correctly correspond with engine revolutions?
I've always thought that it did, but then I made the mistake of thinking "transmission".
SO: if the tranny is in neutral, and you spin the tires one complete circle, and the driveshaft rotates four and a tiny bit, that would be a 4.11 correct? Or does the drive shaft change ratio in any manner coming through the tranny from the engine while in neutral? This is driving me nuts.
I've always thought for 30 years this was an appropriate way to do it but then a friend said "tranny" and now I'm going out of my mind pondering it. Thanks.
I hate thinking.......
Thread Starter
Burning Brakes
Joined: Dec 2005
Posts: 998
Likes: 2
Originally Posted by MikeM
What you are thinking is true if you turn BOTH wheels one revolution. If only ONE wheel turns, you would multiply the driveshaft revolutions by two to get your ratio.
I've got a Posi rear end, but I only physically turned one wheel while Tommy counted the driveshaft rotations.
If I multiplied it by two then I've got an 8.2 rear end gear ratio..
So: I turned the left rear wheel exactly (marked it with chalk) one revolution and the drive shaft turned four and a teeny bit.....
So I'm assuming I've got the 4.11 rear end. Does this make sense???
Drifting
Joined: Feb 2006
Posts: 1,840
Likes: 29
From: Towaco NJ
Originally Posted by Formula Outlaw
I've got a Posi rear end, but I only physically turned one wheel while Tommy counted the driveshaft rotations.
If I multiplied it by two then I've got an 8.2 rear end gear ratio..
So: I turned the left rear wheel exactly (marked it with chalk) one revolution and the drive shaft turned four and a teeny bit.....
So I'm assuming I've got the 4.11 rear end. Does this make sense???
If I multiplied it by two then I've got an 8.2 rear end gear ratio..
So: I turned the left rear wheel exactly (marked it with chalk) one revolution and the drive shaft turned four and a teeny bit.....
So I'm assuming I've got the 4.11 rear end. Does this make sense???
you are making this way to complicated. Simply chalk both rear wheels,
chalk the drive shaft, turn the drive shaft until both wheels make one full turn. Count the number of drive shaft turns and that is your ratio. With a posi. it should be easy.
Pro
Joined: Dec 2001
Posts: 664
Likes: 0
From: Rosamond Ca
Originally Posted by Formula Outlaw
I've got a Posi rear end, but I only physically turned one wheel while Tommy counted the driveshaft rotations.
If I multiplied it by two then I've got an 8.2 rear end gear ratio..
So: I turned the left rear wheel exactly (marked it with chalk) one revolution and the drive shaft turned four and a teeny bit.....
So I'm assuming I've got the 4.11 rear end. Does this make sense???
If I multiplied it by two then I've got an 8.2 rear end gear ratio..
So: I turned the left rear wheel exactly (marked it with chalk) one revolution and the drive shaft turned four and a teeny bit.....
So I'm assuming I've got the 4.11 rear end. Does this make sense???
If your's was an open rear end, you would turn one tire two full revs and count the revs on the drive shaft. The opposite tire will turn in the opposite direction and should not be held or restricted from turning.
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Thread Starter
Burning Brakes
Joined: Dec 2005
Posts: 998
Likes: 2
Originally Posted by vetrod62
you are making this way to complicated. Simply chalk both rear wheels,
chalk the drive shaft, turn the drive shaft until both wheels make one full turn. Count the number of drive shaft turns and that is your ratio. With a posi. it should be easy.
chalk the drive shaft, turn the drive shaft until both wheels make one full turn. Count the number of drive shaft turns and that is your ratio. With a posi. it should be easy.
You're right, I am. That's what I'm assuming we did except I did the turning at the wheel one full revolution, (we chalked both the wheel and the driveshaft) while Tommy counted the driveshaft revolutions. Common sense would tell me that's the same thing as turning the driveshaft and counting until the tire goes around one complete revolution.
Racer
Joined: Jan 2005
Posts: 347
Likes: 0
From: Somewhere in the Finger Lakes of NY
Next time your buddy says 'tranny', send him over to the computer and tell him to google the word 'tranny'. That should keep him occupied for long enough to get your work done.
Thread Starter
Burning Brakes
Joined: Dec 2005
Posts: 998
Likes: 2
Originally Posted by Don Keefhardt
Next time your buddy says 'tranny', send him over to the computer and tell him to google the word 'tranny'. That should keep him occupied for long enough to get your work done.
Great idea....