Why you need a 1350 series drive shaft in your JL Wrangler.

We don't offer a 1310 series drive shaft for a Jeep JL, only 1350. Or 1410 for people who want/need something even more extreme. This decision was made carefully after fully evaluating the different factors that affect required drive shaft strength. I'll explain the details below but first I want to summarize why each of these different factors matters. 

• Vehicle weight. The heavier the vehicle the harder it is to push forward, especially uphill. 
• Horsepower. How much power is available to potentially break things. 
• Torque. Same as above but different. 
• Typical tire diameter. The larger the tire diameter the further the vehicle moves forward per tire rotation which could also be thought of as per X number of drive shaft rotations. The further the vehicle moves, the more effort is required. 
• Relative size and strength of the rest of the drive train components. The strength of the drive shaft should closely match the strength of the transfer case, differential, and axles. It shouldn't be considerably smaller, it shouldn't be considerably bigger. 

For comparison, I'm going to compare a JL to a TJ and skip right past the JK. This is because the comparison is more obvious, because 1310 is the stock size drive shaft for a TJ, and because the JK is a real grey area when it comes to the right size drive shaft but 1350 is often still recommended. 

Here's why 1350 is better in a JL than 1310 and why we don't even offer the 1310 series shafts. We feel that a 1310 is underrated for the front shaft and down right dangerous for the rear shaft. For the JL specifically, we have decided that we would rather lose a customer than to sell someone a shaft for which we are not confident that it will be safe and reliable. 

These newer Jeeps are not your dad’s Jeep Wrangler. For decades a Dana 30, 35, or 44 was the same. It didn’t matter if it was in a Jeep, a Chevy, a Scout, they were all essentially the same. When the JK came out, they called the axles by the same name but they were a bit different. Pretty much all the components were beefed up. Bigger axle joint, bigger pinion shaft, etc. There is a good explanation of this here https://www.dynatrac.com/blog/the-difference-between-new-generation-dana-44-axles-and-older-ones/ . This confuses a lot of people. Naturally they think “Jeep Wrangler, Dana 44; a 1310 series drive shaft has been worked fine in Jeeps for 20 years, why wouldn’t it work now?”. But the newer wranglers and the axles they come with are a far cry from a Jeep Wrangler circa 1990. With the introduction of the JL, things got even bigger. I don’t know about the rest of the axle components but a JL pinion shaft is huge, nearly 1.5” in diameter whereas an old school dana 44 pinion is about 1.125”. Take a look a the photo below and the size difference is immediately obvious.

The splined section of a Dana 44 pinion shaft in a JL is noticeably larger in diameter than a pinion shaft from a dana 60, it is almost the same size as a pinion from a GM 14 bolt. This is also true of the transfer case. A 231 transfer case that came in almost every jeep pre-JK used a 26 spline output shaft. The 241 transfer case that comes in a JK or JL uses a 32 spline output shaft, the same as a 205 or an Atlas! The 26 spline shaft on a 231 is the same size as that of the traditional Dana 44, the 32 spline on a JL transfer case is almost identical to the diameter of the JL pinion shaft. The picture above works to demonstrate the size difference between the transfer case shafts as well. So when people talk about wanting their drive shaft to be the “fuse”, I say that’s fine as long as they aren’t using a 20 amp fuse in a 30 amp circuit so to speak.

A JL is just a bigger, heavier, more powerful vehicle. More weight takes more effort to move. A JL weighs about 1,000lbs more than a TJ, that is a 30% increase in weight. Horsepower, 285 vs 150-190 depending on the motor. Again, a huge increase. And size, the bigger vehicle means more stuff you can load into it and more weight you can add to it. The available torque in a JL is greater, 470 lb-ft compared to 235 lb-ft, all of it, it is all bigger. The 6 speed transmission in the JL means you can stay in the power band more of the time than you could in a TJ. 

With the bigger JL jeep you can run 40 inch tires with just a few inches of lift, something that would have been unheard of in a TJ or YJ. Those bigger tires take more effort to turn because they are moving the jeep forward further per rotation. For rough numbers, one rotation of a 35 inch tire moves the jeep forward about 109”, one rotation of a 40 inch tire moves the Jeep forward about 125”. Think of your tire as a rack and pinion gear. The bigger the tire, the bigger the “gear” and the less mechanical advantage you have in moving all that weight through space. Newer Jeeps almost always run bigger tires than the older wranglers, so the drivetrain needs to be a bit stronger.

So that’s my 15 minute dissertation. Yes, it makes sense to have the drive shaft be less strong than something more expensive like the transfer case. But people are often unaware of just how strong everything is. On the flip side. If a guy with a TJ or YJ or CJ thinks he wants to run a 1350 shaft against his stock transfer case and stock axles, we will say “No you don’t, you’ll be making the drive shaft stronger than the rest of the drivetrain.” The cost difference between buying a 1350 series shaft for your JL and a 1310 series is not that big but the consequences of having an under-rated 1310 series drive shaft break can be catastrophic.