Why does spline count matter in axle strength? - JeepForum.com
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post #1 of 20 Old 01-10-2010, 03:32 PM Thread Starter
SeattleTJ
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Why does spline count matter in axle strength?

Can someone please school me on this please? I am wondering why everyone thinks that having more splines matters in axles. I understand that there is more "teeth" with more splines, but I assume that there is no strength increase with the increased spline count, and are people really having axleshaft failure where the splines are breaking or stripping?

It seems like most axle failures I've read about, or experiences are snapped axle shafts. So is this just an academic argument? I also compared this to ring and pinion gears, where with higher ratio gear sets you are generally getting a weaker ring and pinion because of the smaller contact patch with more "teeth" right?

I am considering upgrading passenger side rear axle shaft but don't want to change the spline count since I already have a detroit locker and upgraded Yukon shaft on the drivers side, that the previous owner broke and replaced. Seems like a lot of money to get a new locker, and two new shafts to get more splines, if that is not a real improvement in strength.


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post #2 of 20 Old 01-10-2010, 03:35 PM
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Actually, the higher the spline count, the greater the contact patch overall. Extreme 4x4 has a good vid on this. I will try and find it.


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post #3 of 20 Old 01-10-2010, 03:36 PM
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Quote:
Originally Posted by rustywrangler View Post
Actually, the higher the spline count, the greater the contact patch overall. Extreme 4x4 has a good vid on this. I will try and find it.
yea, x2, and more splines usually means larger diameter in general. two means of strength increase

the spline contact thing is hard to visualize until you see a good picture.


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post #4 of 20 Old 01-10-2010, 03:37 PM
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Increased spline count equates to increased diameter (i.e. Stronger) axles.

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post #5 of 20 Old 01-10-2010, 03:39 PM
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I'm not very smart, but I think if it has more splines, it is, by default, a larger diameter. The other side of that is, more splines means more surface are of contact meaning less chance of stripping.
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post #6 of 20 Old 01-10-2010, 03:43 PM
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Quote:
Originally Posted by seattleyj View Post
...I also compared this to ring and pinion gears, where with higher ratio gear sets you are generally getting a weaker ring and pinion because of the smaller contact patch with more "teeth" right?...
With the ring and pinion, it's actually less teeth. The ring gear has more but the pinion has less as you go deeper into gears. As said above, the more splines you have the greater the contact area to spread the load.

https://www.jeepforum.com/forum/f9/diy-alignment-kit-steps-w-pics-2264465/
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post #7 of 20 Old 01-10-2010, 03:47 PM
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But as said above, the key here is that where TJs axle shafts are concerned, more spline count = a bigger diameter shaft. A 30 spline shaft has a significantly larger diameter than a 27 spline axle shaft does. Not to mention that aftermarket axle shafts that have more spline counts than stock are not only larger in diameter, they are often (usually?) made with a stronger alloy like chromolly steel.

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post #8 of 20 Old 01-10-2010, 03:48 PM
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typicaly a higher spline count on axles means a bigger axle diameter, for example a dana 60 axle with 35 spline axles has a axle diameter of 1.5 inches as opposed to the 31 spline having something like a 1.2 inch diameter. in addition the greater spline count the greater the contact area between axle and the receiving spider gear. as far as ring and pinion strength, the lower the gear ratio the weaker the pinion typicaly gets and the stronger the ring gear. because a lower geared pinion has less teath, the pinion is much smaller then a pinion gear of a higher ratio differential. the ring gear becomes much thicker within a lower geared differential in order to make contact with the smaller pinion, and the opposite for a higher geared diff
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post #9 of 20 Old 01-10-2010, 03:59 PM
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i got you guys covered as far as pics! haha i've got the show on itunes
heres the overall pic from extreme 4x4 of the splines

and here is the pic of the splines as if under a microscope

as you can see they dont fit as perfect as they feel. they do have a lil play and there for have tiny contact points (the little dots). which means more points or dots means more strength


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post #10 of 20 Old 01-11-2010, 12:59 AM Thread Starter
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Perfect! I learned something new today. I guess that (typically) when they add splines they add axle diameter. So while you could have a 1" 27 spline axle or a 3" 27 spline axle, most of the time you are getting a bigger diameter axle. Therefore the old detroit would not only not have the incorrect number of splines but the axles may not physically fit in the smaller locker housing openings. Is it possible to retrofit or modify my detroit locker to carry the larger and higher splice count axles?

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post #11 of 20 Old 01-11-2010, 01:10 AM
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x2 excellent info. learn something new everyday!
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post #12 of 20 Old 01-11-2010, 08:02 AM
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So then, which is stronger? The 19 spline stub shaft that the Wagoneer uses or the 27 spline stub shaft in the stock unit bearing?

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post #13 of 20 Old 01-11-2010, 08:15 AM
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Quote:
Originally Posted by mrblaine View Post
So then, which is stronger? The 19 spline stub shaft that the Wagoneer uses or the 27 spline stub shaft in the stock unit bearing?
whats the diameter at the splines of each? (correct me i'm wrong, but i think the 27 splines is 1.16"??)


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post #14 of 20 Old 01-11-2010, 08:33 AM
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Originally Posted by ryanwhiteaker View Post
as you can see they dont fit as perfect as they feel. they do have a lil play and there for have tiny contact points (the little dots). which means more points or dots means more strength
more points of contact mean more places to distribute the forces.

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Originally Posted by mrblaine View Post
So then, which is stronger? The 19 spline stub shaft that the Wagoneer uses or the 27 spline stub shaft in the stock unit bearing?
??? the 19 spline. It's a larger tooth with more contact face. ?????


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post #15 of 20 Old 01-11-2010, 08:50 AM
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Originally Posted by never monday View Post
more points of contact mean more places to distribute the forces.



??? the 19 spline. It's a larger tooth with more contact face. ?????
Using that logic, a 10 spline would be even stronger, right?

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