There are many benefits to installing the newer generation Dana 44 JK (rear) ring and pinion into an older generation standard rotation Dana 44 housing, front or rear. Larger ring gear diameter, larger pinion shaft diameter, larger ring gear bolts, larger pinion nut, availability of US made OEM Spicer gears all the way down to 5.38, modern gear cutting technology (OEM only!) to name a few. All JK Dana 44 gears are made “thick”, which means this conversion requires a 3.73 and numerically lower (aka “3 series”) Dana 44 carrier regardless of ratio. It also requires a JK 44 yoke, available in 1310 and 1350 u-joint sizes. Depending on your current configuration, starting point, or direction of your build, the difference in cost between the JK ring and pinion upgrade or sticking with the older generation 44 gear set will vary. The conversion is relatively straight forward. It uses a specific set of pinion bearings to adapt the JK pinion to the older housing. However, because there is a bit more to it than off-the-shelf parts, be cautious of conversion kits on the market. This conversion does require some customized parts.
Back to back comparison of the JK 44 and standard 44 ring gears. Spicer also refers to these Dana 44’s as 226 and 216, respectively, for the diameter of the ring gear in millimeters. The JK ring gear being 10mm larger in diameter, or just over 3/8″. The standard Dana 44 housing has enough internal clearance to accommodate the larger JK 44 ring gear without modification.
The JK 44 pinion shaft boasts a significant increase in diameter from top to bottom vs. the standard 44 pinion shaft. Both inner and outer bearing surface diameters are significantly larger, the spline diameter is larger despite the lower spline count (course 24 spline vs. fine 26 spline), and the thread diameter is larger utilizing the Dana 60 pinion nut.
With exception of the ’07 model year, the JK Dana 44 uses 1/2″ ring gear bolts with a 125-135 ft-lbs torque spec. (OEM bolts). Standard 44 ring gear bolts are 3/8″, but were upgraded to 7/16″ for the ’03-’06 TJ (aftermarket gears are generally dual drilled). Installing a JK ring gear on a non-JK carrier requires drilling the carrier for 1/2″ bolts.
Spicer manufactures all JK 44 gear sets using the modern face-hobbing (2-cut) machining process, whereas the previous generation Dana 44 Spicer gears are manufactured with the older face-milling (5-cut) process. Note the difference in tooth profile between the 2-cut (right) and 5-cut gear sets. 2-cut gears set up differently, with a pattern that sweeps across the tooth. 5-cut patterns are flat and rectangular. Almost all aftermarket ring and pinions, JK included, are manufactured using the old 5-cut process.
Making it work
My version of the install uses a custom made bearing race spacer that is machined to the correct thickness to allow use of the OEM Spicer JK pinion depth shim. This spacer is key to a clean and proper installation and is one of two critical areas of the conversion I have seen executed poorly.
Before the inner conversion race can be driven into the bore of the housing it is necessary to cut reliefs into the seat. These reliefs don’t already exist because the standard 44 bearing race has a large shoulder which overhangs the seat and is accessible with a drift.
The custom machined spacer is dropped into the bore before the race is driven in.
The spacer tucks neatly behind the race locating it at the correct depth. There are kits on the market that attempt this with combinations of incorrectly sized shims which don’t fit properly in the bore and make contact with the bearing cage.
Note there is NO overhang of the spacer or bearing race beyond the seat of the housing bore. Being machined to same OD as the bore and ID as the back of the race eliminates any concern of the spacer contacting the bearing cage.
A look from behind with the spacer and inner race installed. Having the spacer machined to the correct thickness to allow me to set pinion depth using the OEM under-bearing shims, the race does not need to be removed for setup purposes. However, the reliefs are necessary if the race is to be changed in the future.
The OEM pinion depth shims are hardened steel and vary in thickness by .001″ increments from one size to the next.
A single shim of the correct thickness is selected to set the proper pinion depth. The hardened steel shim is designed for longevity, where a stack of soft aftermarket shims will compress and deform causing the setup to change leading to premature failure.
The outer bearing/race combination used to achieve the conversion is much taller than the original. Notice how the race blocks a portion of the oil galley opening. Enlarging the opening helps offset the blockage.
The taller outer bearing sits extremely close to the pinion seal, creating two problems. The first is the sealing surface of the yoke can not engage the lip of the seal. Instead, the smaller diameter of the leading beveled edge of the yoke rides inside the lip of the seal. The second problem is it results in fewer exposed pinion threads which are unable to fully engage the pinion nut. Without utilizing the full depth of the pinion nut, the pinion threads fail to reach the Stover (pinched end of the nut).
The yoke must be machined and shortened sufficiently for the full diameter of the yoke’s seal surface to engage the pinion seal lip and for the pinion threads to fully engage the Stover of the pinion nut. This crucial step is often ignored with off-the-shelf conversion kits and creates potential for a leaking seal or losing the pinion nut.
The carrier installs as it would with the older generation 44 gear set. The JK ring gear clears the housing with enough room to comfortably route the ARB copper line across to the bulkhead fitting. This conversion was installed into a front Wagoneer Dana 44. With the inherent weakness of the low pinion front end due to increased deflection from driving on the coast side of the gear, it benefits greatly from the additional strength offered by the JK 44 gear set.
Bull Built Differentials 