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Nuts & Bolts: High vs. Low Pinion

Posted in How To: Tech Qa on July 11, 2017
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I often hear that a high-pinion front axle is stronger than a low-pinion axle, but no one can seem to tell me why. What’s the deal? How much stronger is a high-pinion Dana 30 compared with a low-pinion Dana 30, for example? Is a high-pinion Dana 30 stronger than a low-pinion Dana 44?

Josh H.
Via nuts@4wor.com

Great questions! It’s common knowledge that a high-pinion front axle is stronger than its low-pinion equivalent, but not everyone understands why. A low-pinion axle positions the pinion below the centerline of the axle, while a high-pinion axle places the pinion above the centerline of the axle. The OEMs have used both styles in solid front axles over the years in many different solid-axle applications.

If you look at the teeth of a ring gear, you will notice that one side of each tooth is nearly vertical while the other side has more of an angle. The sharper of the two sides is the drive side of the gear, while the more gradually angled one is the coast side. In low-pinion front axle applications, engine torque is actually applied to the coast side of the gear (so the gear drives forward on the coast side), whereas on high-pinion applications engine torque when moving forward is applied to the normal drive side. By design the coast side of the gear is weaker, so a low-pinion front axle is going to be weaker than its high-pinion equivalent.

We posed your questions to some experts at both Nitro Gear & Axle (nitro-gear.com) and Motive Gear (motivegear.com) to see what they had to say. While neither company had hard data or empirical numbers that they could share with us regarding high- and low-pinion front axles, both agreed that in terms of just the ring-and-pinion in otherwise identical housings (such as high- and low-pinion Dana 30s), the high-pinion gears are stronger.

How much stronger? We weren’t able to find anyone who could give us hard numbers, but both experts were quick to point out that there is much more to it than which side of the gear the engine torque is being applied to. Axleshaft diameter, axletube thickness, differential style, knuckles, hubs, and much more have a great deal to do with the overall strength of a front axle.

A stock high-pinion Dana 30 out of an XJ is going to be marginally stronger than an XJ low-pinion Dana 30, but a low-pinion Dana 44 is going to have much more strength than a high-pinion Dana 30 for several reasons. The larger, 8 1/2-inch-diameter ring gear of a Dana 44 is going to have much more tooth engagement (surface area) than the 7.2-inch-diameter gear of the Dana 30, and tooth contact is going to play more of a role in strength than which side of the gear the engine torque is being applied to. This is why larger-capacity axles (Dana 60, 14-bolt, and so on) have larger-diameter ring-and-pinions to match.

The pinion gear shafts (another common failure site) are also different diameters. Dana 30s have 1.18-inch-diameter, 27-spline axleshafts that are smaller than 1.31-inch, 30-spline Dana 44 axleshafts. Those numbers might not seem significant until you realize that strength ramps up exponentially with every few thousandths of an inch in diameter. Axletube thicknesses can vary widely according to the age and application of both axles.

On top of all of this, there are aftermarket upgrades available that can beef up many different components of each axle, which further middies the waters for this discussion.

This is a long-winded answer to a seemingly simple question, but the bottom line is that many factors are involved in axle strength beyond just the ring-and-pinion or the pinion’s position relative to the centerline of the axle. Specific to Dana 44 axles, it is worth noting that the newer JK Dana 44s (and Dana 30s, for that matter) use pinions of significantly larger diameter than the older models. In fact, the diameter is equivalent to that of a Dana 60. As a result, Nitro Gear & Axle and a few other companies have released retrofit gears that allow standard-rotation Dana 44s to be upgraded with the newer and stronger JK-style ring-and-pinion sets. This is great news for any older Dana 44 applications, of which there are many among almost all of the OE manufacturers.

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