What are splines and how does a different number affect the car? Thinking about buying a 9 inch with locker and curious what the difference is between splines...

 

higher spline count can handle more torque.

 

More splines usually mean larger axle dia. as well. Thats why the torque rating goes up so much as the spline count increases.

 

Ahhh so it's always best to pick the highest number of splines??

 

Generally it is, for a street car with limited track use its not a huge consideration. Moser has a calculator on their site that helps determine axle size needs, its designed to give you at least 2x the needed strength and cut down on the extra weight if needed.

I'll see if I can find it....

 

Here it is, its pretty sweet explaination.

http://www.moserengineering.com/Pages/axletech.html

 

Not always. Higher spline count can mean a thicker heavier axle. This can hurt performace a touch if not needed. Most of the people on here will never exceed a 33 spline 12 bolt or 35 spline 9" axle capacity.

 

What are your goals for this 9" Rear?

Jeff

 

If weight is a concern they also have axle lightening options, the bigger you go the more it weighs but the stronger it is.

A 40 spline axle is heavier and stronger than a 35 spline axle, but if you get it gundrilled, where they remove material from the center of the axle so it now looks like very thick tubing, it is stronger than a 35 spline non drilled axle but now lighter.

Like mentioned it depends on what you want to do.

If you run a posi or locker you'll be limited to a max size spline, if it is a 12 bolt you'll be limited as well to 33 spline, I think most people only gun drill 35-40 spline axles, I personally wouldn't run a 33 spline gun drilled axle even if they did do it.

If it is a spool you can run the bigger 35 or 40 splines and have them gun drilled.

On my car I am going 40 spline, will it weigh more than a smaller axle, sure but do I care, not really. I will gun drill them if money permits, depends how nice uncle sam is at tax time, but either way I am getting 40 spline and care more about durability than gaining a few thousandths in a 1/4 mile.

Also you don't hear too many stories of a car making under 600 hp breaking 40 spline axles. I've never heard any. When I make more power I am good to go.

If you're going with a 9" with a locker run a 35 spline axle, buy the strongest stuff you can get with your locker, whole point of buying your 9" is so you don't have to worry about it breaking like the POS 10 bolts these cars come with, build it once and build it to last, it's easy to add power, why pay more money to add better parts later when you can do it and be done with it.

You could also have a 35 spline gun drilled axle which would be a pretty cool combo with a locker in a street strip car.