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axle ratio

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dodjh View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dodjh Quote  Post ReplyReply Direct Link To This Post Topic: axle ratio
    Posted: 25 Apr. 2015 at 1:24am
I've searched the site for posts on finding axle ratio and have come up short.

How do you determine axle ratio by counting rotations of wheel and drive shaft?

Thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 1:34am
1. Jack up rear tire (one side only)
2. Spin the wheel 2 times
3. Count revolutions of the drive shaft.

That's your ratio

Edited by jpet - 25 Apr. 2015 at 1:36am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote danover321 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 1:34am
If you have the standard CJ2a Dana 30 and Dana 41 you will have a 5:38 gear ratio.  If you have the military Dana 27/23 you will have a 4:88 gear ratio.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Thorholt Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 1:38am

Put a mark on each rear tire on the inside of it so you can see it easily then mark the pinion the same way, then using both hands turn both rear tires exactly one turn in the same direction while counting how many times the pinion rotates, if the pinion turns about 4 and 1\4 turns you have 4.27 ratio, if it turns 5 and a 1\3 turn you have 5.38. It's not exact but will get you close on ratio.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote dodjh Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 2:16am

It is the military Dana....so if I spin the rear tires 2 complete revolutions and the drive shaft spins
4 times, that would be a 4.88 ratio?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dodjh Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 2:35am
Okay, I marked D.S. and 1 rear tire that was off the ground.  I spun the tire 2 complete revolutions and the D.S. spun 5 1/3  times.   5.38?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dodjh Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 4:07am
Thorholt...I don't follow your method....do I remove the pumpkin cover to mark the pinion gear or mark the D.S. yoke on the outside?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepFever Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 5:04am
Originally posted by dodjh dodjh wrote:

Okay, I marked D.S. and 1 rear tire that was off the ground.  I spun the tire 2 complete revolutions and the D.S. spun 5 1/3  times.   5.38?
 
Yes  :)    5.38
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Thorholt Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 8:38am
Just make a mark on the yoke, drive shaft, what ever that is easy to mark, you just need that mark to count how many times the pinion turns. Spinning one tire might work on a Jeep but if you spin only one tire you are including the spider gears into the equation, they don't effect the actual ratio but they might give you a false ratio, do what you want, I am just giving you the easy way to do it

Edited by Thorholt - 25 Apr. 2015 at 9:09am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 10:42am
Originally posted by Thorholt Thorholt wrote:


.......... Spinning one tire might work on a Jeep but if you spin only one tire you are including the spider gears into the equation, they don't effect the actual ratio but they might give you a false ratio, ....

With all due respect, This is incorrect . One tire is jacked up. One tire is solidly on the ground and can't turn. This is why you spin the wheel twice. Because the differentials distribute the power for both wheels to the one that is free spinning.

Both wheels going down the road straight, is even distribution (1:1). When you make a turn, if the inside wheel is turning 33 percent slower, the ratio would be .5:1.5 inside to outside wheel. .... so when one wheel is held solid, all the drive is distributed to the spinning wheel (2:0) so in a nutshell, one wheel spun twice is equal to two wheels spun once.
Quote ..do what you want, I am just giving you the easy way to do it

No. That method requires you to jack both wheels up, spin both wheel in perfect sync, while trying to look at the driveshaft.

If you jack one wheel up, and leave the other on the pavement, you can spin the wheel twice with one hand, not worry about trying to spin two wheel together equally, and never take your eyes off the drive shaft. Easier, safer, more accurate.

To answer the original posters question, your ratio is 5.38 since you got 5-1/3 revolutions after spinning one wheel twice.
The true ration is 5.375:1.

If you want to do a dead nuts confirmation, jack up one wheel, put a timing mark on the drive shaft, spin the wheel 16 times. When you stop the drive shaft timing mark should be in time with the pointer because the drive shaft would have spun exactly 43 times.

5.375:1 = 43:8.
Differential ratio (spinning wheel twice) = 2:0
Final ratio: 43:16

Edited by jpet - 26 Apr. 2015 at 12:57pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 52 M38 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 11:58am
And in our next episode JPet will explain the equations behind Eistein-Rosen Bridge Wormhole theory and how that relates to twin stick D18 warp drives.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rocketeer Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 12:08pm
Originally posted by dodjh dodjh wrote:


It is the military Dana....so if I spin the rear tires 2 complete revolutions and the drive shaft spins
4 times, that would be a 4.88 ratio?

When someone says "military" they mean a WWII full floater. Is that what you have?

Larry
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 1:26pm
.... I suppose I should add then that if you jack up one wheel, spin it 16 times and the drive shaft makes exactly 39 revolutions, you have a 4.88 ratio or actually 4.875:1
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dodjh Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 1:34pm
rocketeer, it is a post WWII Jeep....'53'.

jpet, thank you for your post.

JeepFever, thank you for your post.

Thorholt
,thank you for your advice.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote danover321 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 2:54pm
Did the early CJ2a's with the full floating axle have 4:88 or 5:38?  I had the belief they were 4:88 until the production change to the Dana 41.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote autolite Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 4:56pm
All came with 5:38's. Only WWII M.B./GPW came with 4:88.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote danover321 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr. 2015 at 5:29pm
Originally posted by autolite autolite wrote:

All came with 5:38's. Only WWII M.B./GPW came with 4:88.


My eyes have been opened!

Thanks,

Dan
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dodjh Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep. 2015 at 10:26pm
If I jack up one rear tire, put trans. and T/C in neutral, mark drive shaft and tire, after one revolution the DS spins 2 1/3 revolutions.

If I spin the tire 2 revolutions the DS spins 5 1/4 revolutions.

What is my axle ratio?

Thanks
"COURAGE IS BEING SCARED TO DEATH
-BUT SADDLING UP ANYWAY"
               JOHN WAYNE








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