You've heard us harp on the subject for years without once changing our tune; running an automatic locker in therear of a short-wheelbase Jeep can make for a miserable on-road driving experience. An automatic locker functions very simply. It's locked when power is applied to the axles and unlocked when no power is applied. That means every time you get on and off the gas, the locker locks and unlocks. The handling drawbacks manifest themselves when this happens in the middle of a turn, changing lanes, or negotiating curvy sections of road. On some Jeeps with supple suspensions, especially link-type suspensions, the locker actuation can cause the Jeep to change lanes or shoot violently to one side or the other. It's something the average enthusiast will become accustomed to rather quickly, but for us the acid test is always, "would I toss the keys to a non-enthusiast, my wife, or a valet?"
We wanted to see if we could take steps to improve these handling drawbacks. Granted, our stock-height, leaf-sprung '89 Wrangler test vehicle is a best case scenario for the auto locker, while the worst-case would be a TJ with a manual transmission, tall short-arm suspension, and larger tires.
Since we can't in good conscience recommend installing a locker of any type in a stock Dana 35 rear axle, we called Superior Axle & Gear for its Super 35 kit. This kit includes an Eaton Detroit Locker, Superior's superb 30-spline, 1.31-inch alloy axleshafts (stock Dana 35 is 27-spline, 1.16-inch), and a full installation kit. This would ensure we don't suffer any breakage during our testing. So after all our efforts are we satisfied? Nope. Although it helped a little, we still wouldn't toss the keys to a novice. It's still better to run a selectable locker or spool if you're concerned with street handling.
 Aside from mooching some time...  Aside from mooching some time on a buddy's shop press to install the axle and differential bearings, we installed the Superior Super 35 kit ourselves in the driveway. You'll need a dial indicator to measure the ring gear backlash with the original diff. As an indication of Eaton's tight quality control we obtained the same backlash using the stock shim packs on the new Detroit Locker. |  Theory #1: Although upgrading...  Theory #1: Although upgrading to alloy replacement shafts should be considered mandatory for anybody putting a locker in a Dana 35, the larger 30-spline, 1.31-inch Dana 35 shafts in Superior's Super 35 kit should minimize torsional play within the shafts, theoretically minimizing unwanted locker engagement and disengagement.Conclusion: We only ran the larger shafts, so we can't comment on the difference as compared with stock-diameter shafts. |  Theory #2: If your tire pressure...  Theory #2: If your tire pressure is off from side-to-side it will affect the overall diameter of your tires and may cause locker chatter and increase unwanted engagement and disengagement.Conclusion: We intentionally put our rear tires to 32- and 22-psi and noticed a marked increase in the violence and frequency with which our locker engaged. Check your tire pressure. |
 Theory #3: Your tires may...  Theory #3: Your tires may have manufacturing variances in diameter as wide as 1-inch; especially with taller tires. Like the pressure difference, the differing diameters will cause the locker to lock and unlock more frequently since the shafts will be turning at different speeds.Conclusion: We drew a chalk line on our tires with a straight edge and then rolled the Jeep, marking corresponding chalk lines on the driveway. Our measurements were nearly identical, but our tire diameter is small. Differences may be more drastic with larger tires. |  Theory #4: If your Jeep's...  Theory #4: If your Jeep's four-wheel alignment is not within spec, the crabbing and scrubbing effect will accentuate the negative handling effects of the locker.Conclusion: It's a moot point on a leaf-sprung vehicle like ours because there's no easy way to change the front and rear axle's alignment in the chassis, but on a link-type suspension (especially with aftermarket adjustable control arms) careful attention should be paid to making sure the front and rear axles track in the same path and that the wheelbase matches from side-to-side. |  Theory #5: Small-diameter...  Theory #5: Small-diameter axletubes will allow enough flex to adversely affect the locker's function. When the tube bends either vertically (up or down) or horizontally (front to back) the locker may engage and disengage as if the vehicle is negotiating a turn.Conclusion: After running the locker with the factory diff cover, we installed Superior's newly-improved Super 35 axle truss. The new truss installs in three pieces and the fit is good, only requiring some slight tweaking of the factory brake lines. Superior claims the truss decreases vertical flex by 35-percent and horizontal flex by 52-percent. We definitely noticed a marked improvement in unwanted locker engagement and disengagement. |