Helical worm-gear limited slip carrier for a Dana 30 front axle with 27-spline axle shafts and a 3.73 or numerically higher ratio. SL D30-4-27-LSD.
If your Jeep's front axle spins one tire on a muddy climb or a snowy driveway while the other tire sits still, the open carrier in that Dana 30 is doing exactly what it was built to do, and that is the problem. This helical worm-gear limited slip, part number SL D30-4-27-LSD, drops into a Dana 30 front axle with 27-spline inner shafts and a 3.73 or numerically higher gear ratio. It is sold as the Spartan Helical LSD and gives you traction help without clutch packs, air lines, switches or wiring.
An open front differential always sends equal torque to both sides, so the tire with the least grip sets the limit for both. A helical unit replaces the spider gears with ten helical-cut pinions that mesh with the side gears. When one tire starts to spin faster, the gear separating forces load the pinions against their pockets in the case, and that friction biases torque toward the tire that still has grip. There is nothing to engage and nothing to wear out the way clutch plates do, so it pulls smoothly instead of the on-off bang of a locker. With ten pinions there are more contact points to share the load than in a six- or eight-pinion design. The case and internals are forged 8620 steel.
Know the one limit before you buy. If a front tire is completely in the air, there is no load to bias against and the axle can act open. A light touch on the brake pedal adds resistance and sends torque back across. In 4WD you may notice slightly heavier steering in tight turns. With the front disconnected in 2WD you will not feel it at all.
Dana 30 carriers come in two sizes. Axles geared 3.54 and numerically lower use the smaller case, and 3.73 and numerically higher use the larger one. This unit is the 3.73-and-up case only, and it will not bolt to a 3.54-down ring gear. Read the ratio from the axle tag on the cover bolts or stamped on the ring gear, or count teeth on the ring and pinion and divide. Then pull an inner shaft and count splines: you need 27. If you are re-gearing from a low numeric ratio at the same time, this case suits the new 3.73-up gears. Eaton's Truetrac is built on the same carrier split, and the Detroit Truetrac 27-spline 3.73-and-up front is the comparison most buyers look at.
If you would rather keep the front fully open and simply repair broken spiders, the Yukon Dana 30 open spider gear kit is the low-cost route.
Dana 30 front, 27-spline axle shafts, 3.73 and numerically higher ratios. The Dana 30 front was used under many Jeep Wrangler and Cherokee models, but spline count, carrier break and ring gear rotation vary by year and package, so confirm all three on your axle rather than going by model name. If you are not sure, send us the year and VIN with a photo of the axle tag before you order. You can browse the rest of our axle hard parts in the hard parts section.
After the first 500 miles, change the gear oil and look at the magnet. Fine paste is normal break-in; chips are not.
| Axle | Dana 30 front |
| Axle spline | 27 |
| Carrier break | 3.73 and numerically higher ratios only |
| Type | Helical worm-gear limited slip, 10 pinions, no clutches |
| Part number | SL D30-4-27-LSD |
| Weight | 14.47 lb |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. Dana 30 carriers split at the ratio. This is the 3.73-and-up case. A 3.54 or numerically lower ring gear needs the smaller carrier, so either buy a 3.54-down unit or re-gear to 3.73 or higher at the same time.
No friction modifier. The recommended oil is non-synthetic 80W-90 GL-5. There are no clutch plates to condition, and normal gear oil changes are the only service.
New carrier bearings, new ring gear bolts and thread locker, gear oil, and usually new inner axle seals. If you do not own a dial indicator, bearing puller and press, plan on a gear shop for the setup.
In 4WD you may feel a little more steering effort in tight turns because the unit resists wheel speed differences. In 2WD with the front disconnected there is no change in steering feel.
A helical unit needs some load on both tires to bias torque. With one tire fully off the ground it can act open. Lightly applying the brakes adds that resistance and sends torque to the tire on the ground.
