Beefing Up Axleshafts, Driveshafts, and Gears on a Jeep LJ WranglerPosted in How To: Suspension Brakes on October 29, 2015
Once we had 35-inch tires on our ’05 LJ (with future plans to possibly go with bigger rubber one day), it was a no-brainer that the Jeep’s ring-and-pinion gears, axles, and axleshafts should be beefed up to handle the increased bite and weight of the tires.
Large, high-traction tires can break or twist OEM axleshafts, and having used RCV Performance axles for two previous Jeep builds, we knew that was a safe bet. So we looked into the company’s front axle set with CV joints instead of U-joints. Not only are CVs smoother when at full-lock turns, they are far stronger than similarly sized U-joints. Alloy USA uses the latest cold-rolled splining technology to produce splines that are stronger than those that are traditionally cut. The Alloy USA rear axleshafts also come with a 10-year warranty.
When it came to the gear sets and differential rebuild kits for the front and rear, we chose Yukon Gear and Axle. All the parts needed to get the job done are included. The Yukon master kits will ensure exacting fit and hassle-free installation with top-notch components such as Timken bearings. Assembling gear sets properly is not for the inexperienced mechanic, nor for the experienced tech without the proper tools. If you’re even the slightest but nervous about this operation, farm it out to an expert. A little extra cost can keep you four-wheeling instead of sitting by the road weighting for a tow truck.
Choosing the right ratio gears was a breeze because we used the gear comparison calculator on Summit Racing’s website (summitracing.com). We used a gear set that would keep the engine speed the same or slightly higher than it was with the stock gear/tire combination at the same road speed. With the Yokohama Geolander M/T’s 35-inch diameter, we determined that 4.56:1 gear ratios would give us an engine speed of a few hundred rpm above the stock gear/tire combo.
With the 4-inch lift we installed in Part 1 (Feb. ’15), we also needed a longer rear driveshaft. The front driveshaft didn’t need to be replaced because it was a double Cardin-style CV joint, while the rear had a slip-yoke/U-joint design. We contacted Powertrain Industries for an upgraded rear driveshaft: a 1310 double Cardin-style CV (constant velocity) driveshaft. Although somewhat light-duty compared to the 1350 series normally seen on pickup trucks, the 1310 is plenty strong for our application, and Powertrain’s design is old school with the slip joint on the differential end.