What I'm wondering is why the splines on an axle are so small, while the ones on a tranny or T-case shaft are bigger???

I know axles used to have coarse splines, but they moved away from that.

Why wouldn't it be stronger to have the end of the axle look like a big plus sign (essentially 4 splines)???

I'm guessing it has something to do with the properties of materials of the metal......????

with more splines you are going to have more surface contact then if you had one big spline. More splines is better......to a point

The bigger the splines the deeper you cut so the x-section of the axle gets smaller.

So, what you're saying that the way the splines are is a copromise between crossection diameter and stregth of the splines themselves.

It just seems there isn't much metal involved in keeping the splines from spinning/twisting...

look at the circumferance of the shaft at the bottom of the grooves. more splines dont' have as much force on each spline as big splines do. and small splines have a bigger uncut shaft then the same overall sized shaft w/ big splines

More splines add strength...The more splines the larger the circumfrence. The bigger that gets, tteh more torsional strength you get.

:beer: :beer:

What is stronger a 3/8 Fine or 3/8 course thread. You will be more likely to twist the head off the course thread due to the amount of bolt removed to make the threads.

Originally posted by Kicker
More splines add strength...The more splines the larger the circumfrence. The bigger that gets, tteh more torsional strength you get.

:beer: :beer:
Been there done that :) Just ask rockbuggy.. he broke the head off one of the bolts that holds the halfs of my t case together, because that was the only way we were going to get the t case apart to do the SYE.. man was it funny LOL :D
Scott :grinpimp:<><

Originally posted by wrangler40
What I'm wondering is why the splines on an axle are so small, while the ones on a tranny or T-case shaft are bigger???

The minor spline diameter (diameter of the shaft cross section at the base of the spline points) is the weakest area of an axle because it is the narrowest.
More splines = smaller splines = greater minor spline diameter for a given diameter of axle shaft.

The reason they don't have all those splines on a the engine-tranny and tranny-transfer case shafts is simply because they aren't needed yet. This is because the torque has not yet been multiplied enough to get anywhere near their breaking points. Whereas, your axle shafts see anywhere from three to twenty five times the amount of tourque that the tranny-transfer shaft case sees and from three to over one hundred times the amount of torque that the engine-tranny shaft sees (dependent upon gearing).

The gears in your transmission, transfer case (when it's in LO gear), and differential all multiply the amount of torque.

Example:

A Wrangler with an inline six makes around 210 lbs-ft of peak torque. So that's all the torque the shaft between the engine and tranny sees.

First gear in an AX-15 is 3.83 to 1. So the maximum amount of torque that the transmission-transfer case shaft will see is approximately 804.3 lbs-ft.

The NV-231 in 4-Lo further multiplies the torque by 2.72 bringing our theoretical maximum torque figure to 2187 lbs-ft which is then multiplied again by the differential to 3.07 for a grand total of 6716 lbs-ft of torque.

Since the differential divides power and torque eqally between the two shafts, the most torque you'll theoretically see on a single shaft (in your rear axle assembly) is only 3,358 lbs-ft. However, in a vehicle equipped with a locker, each axle could see the theoretical maximum of 6178.

In the real world the axles would never see this much torque due to parasitic losses from friction in your drivetrain and the fact that you'd have to be parked up against a brick wall, dropping the clutch at full throttle in order to come anywhere close to our "theoretical maximum." There's also the fact that the front end will see less torque than the rear end because it will always be sharing power with the rear end, whereas the rear end has to work alone most of the time. That said, it's still a sheeyit load of torque and it's the reason that axle shafts have to be much beefier than the shafts connecting components further up the driveline.

By way of comparison, the maximum theoretical amount of torque seen by each axle in the same vehicle with an NV4500 (with the 6.43 to 1 first gear), a 4.3 to 1 Atlas, 5.13 gears and lockers is around 29,786 lbs-ft. Ouch!

HTH,
Jake Harsha

Ok Jake, since you seem to know what's goin on, what about the jerking forces experienced with wheelhop. Climbing a hill, and you get that "chunka chunka chunka" from the tires grabbing and letting go. Got any idea what the torque is coming off of the tire's friction with the ground? I guess it's however much torque it takes to slow the tire+axleshaft+driveline down to whatver speed it spins at while the tire is on the ground??

Also, if you or any other Mechanical Engineers out there know, what's a typical coefficient of friciton for an aired down tire on rock (or dirt or anything)?

Originally posted by wrangler40
Ok Jake, since you seem to know what's goin on, what about the jerking forces experienced with wheelhop. Climbing a hill, and you get that "chunka chunka chunka" from the tires grabbing and letting go. Got any idea what the torque is coming off of the tire's friction with the ground? I guess it's however much torque it takes to slow the tire+axleshaft+driveline down to whatver speed it spins at while the tire is on the ground??

Also, if you or any other Mechanical Engineers out there know, what's a typical coefficient of friciton for an aired down tire on rock (or dirt or anything)?

Well, without any testing equipment... ;)

But seriously, the "chunka, chunka, chunka" thing you're talking about is caused by the axles winding up to the point where the amount of torqe being applied to the axle exceeds the amount of friction and leverage at the outside of the tire and the tire breaks traction and lets go. The axles actually twist as much as 1/8th of a turn (or more depending on the alloy) without breaking.

I can't give you any particulars, only that the amount of torque seen by the axles increases exponentially as the size of your tires increases. This is because of the the added leverage of a larger-circumference tire needs less friction (read traction) to overcome a given amount of applied torque. This is also why big tires + little axle assemblies = Broken axle shafts.

Jake

coefficient of friction varies, of course, on the compound of the rubber and the material being driven upon.

i think your average cf of a tire on dry pavement is gonna be about .6 or so. not quite sure on that.

aired down tires only give you marginally more friction. you get assloads of surface area to excercise that friction on tho ;)

jakester is right on the torqueyaxlephysics stuff. *sigh* i can't wait to start my physics classes next semester! i hate chem:(

http://sniperfire.rockcrawler.com/images/splinedamage.jpg

Superior shafts went in this past weekend...