Importance of Splines

[uranium67]

Can someone tell me what splines are and the importance of them, as well as what it means when I have a 4.56 gears in my differential?
I'm looking for a good rigging for my '64 F100 to make it more rugged, maybe for off-roading, so any suggestions would be greatly appreciated!
Thanks!

[leolkfrm]

4.56 gears lots of pulling power, no speed!

[75K30]

Originally Posted by leolkfrm

4.56 gears lots of pulling power, no speed!

Not so sure that this is an entirely true statement there leo. Dont forget to factor the tire size, (what if this vehicle is running 42" tires?) or the rpm. Remember speed is directly proportional to horsepower. Very seldom is the gear reduction so low that the vehicles speed is limited.

Take a drag car for example, and use 2.75 gears and compare them to 4.88's. The only things that will vary is the ET, and the vehicles ability to launch. Believe this or not but the miles per hour at the end will be the same, provided that the 2.75 gear set does not boil the tires. In this case the mph will be higher, unless it boils the hides all of the way down the track, then the mph through the traps will be lower.

Lets consider a 5 hp briggs engine. Can this engine pull a 1:1 ratio? Answer is yes, if the vehicle is light enough it can, but it will accelerate very slowly, and reach a top speed after a long period of time. Create a mechanical advantage with a better gear ratio and the vehicle can accelerate much faster. This compensates for weight too.


For the OP. Splines are the tiny teeth that the axle has on the end where it interfaces or engages with the side gear in the differential. Spline count is important for strength, and fit. You must have the same number of splines in order for an axle to interchange with other componets. Now your yoke on the pinion also has splines, and the same examples as above are true for these.

Typically the more splines the better. Coarse splines (while rather rare now, but you are working with an older truck) are considered weaker than fine splines. FIne splines create a better contact area and have a greater amount of contact making them stronger. Larger axles will have the greatest number of splines, also making them stronger based upon size and spline contact.

Here is the splined end of an axle:

[batty1214]

OUCH^^^^^ that doesn't look like it was a good thing.....

[leolkfrm]

well I thought the simple answer would be the best, as I don't think he is into racing set ups. but, --68 chevy pickup with 4 speed and big rearend gears, needs to draft to get over 55mph, but has the torque to pull a house getting there.

[75K30]

Originally Posted by leolkfrm

well I thought the simple answer would be the best, as I don't think he is into racing set ups. but, --68 chevy pickup with 4 speed and big rearend gears, needs to draft to get over 55mph, but has the torque to pull a house getting there.

yes sir, point taken

[bradrhale]

Originally Posted by uranium67

Can someone tell me what splines are and the importance of them, as well as what it means when I have a 4.56 gears in my differential?
I'm looking for a good rigging for my '64 F100 to make it more rugged, maybe for off-roading, so any suggestions would be greatly appreciated!
Thanks!

this means that the driveshaft will spin 4.56 times when the axle shaft spins one time. the higher that number, the more turns of the driveshaft you have, thus making you have a higher mechanical advantage. the lower the number, the less rotations of the driveshaft but this can give you more speed on open flat as the engine doesnt turn so hard to give you the same amount of rotations as a lower geared (higher numerically) rearend.

[Rago]

I made a diagram to show the increased contact area that a higher spline count will give. This may help you to understand better:

[uranium67]

That explanation did it bradrhale. So, when i have a low gear number, say 2.28 I get more speed, but a high number, say 4.48 I get better torque? The diagram also cleared it up too Rago. Im guessing i have a pretty good number if I want to do rock crawling or what not haha

[batty1214]

yeah..... you want a good number of splines and a low gear ratio(like 4:88 or something like that.)