Testing Tera's T-locker
When it came time to finally install a locker in the rear of our Project Hatari! '71 CJ-6, our extremely picky criteria limited our options. In short, we wanted spool-like traction off-road and a stock, open differential on-road. After installing a full onboard air system (Air On Board, May '06) we ordered up a T-Locker (PN TL442-30) from Teraflex for our vehicle's 30-spline Dana 44 rear.
The T-Locker is unique in the pneumatic locker world in that it uses 80 psi to engage the air cylinder that operates the shift fork and doesn't use any internal seals or electrical solenoids. The entire air system stays outside of the diff cover. Basically, after installing the locker, you plumb a source of onboard air to the actuator switch, then two air lines run from the switch to air cylinder on the diff cover. It's that easy. The T-Locker is a severely beefy piece of equipment. The highlights are a 3/8-thick diff cover, protective shield for the actuator cylinder, a machined carrier with hardened pins, and a steel shift fork (not aluminum). If a sudden loss of air pressure is experienced, a spring forces the shift fork back to the open differential position.
Here's what you get when you order a T-Locker from Teraflex. The machined carrier is quite substantial and contains hardened pins that, when engaged, lock the forged spider gears together to form a spool. You can see the air cylinder on top of the diff cover that actuates the shift fork. The cylinder mounts outside the diff cover, so there's no chance of internal air leaks. All the pneumatic fittings and lines are included.
To handle the installation, we brought the Jeep down to TAG Motorsports in Escondido, California. It was somewhat comical to see our rusty project vehicle on a lift along with $80,000 diesel pickups and brand-new Unlimited Rubicons, but TAG doesn't discriminate and welcomed our pile with open arms. As usual, Jay Miller handled the install, including transferring our carrier bearings onto the T-Locker, setting the backlash, adjusting the shift fork, and running the air lines.
So How Does It Work?
We mounted our pneumatic switch right in the dash, so there's a definite and audible psssst when the locker is engaged or disengaged. When engaged, air pressure forces the shift fork one way. When disengaged, the air pressure forces the shift fork the other way. It doesn't rely solely on the fork return spring to disengage.
Obviously, the locker behaved just like an open differential when disengaged and like a spool when engaged. Judging from the nearly nonexistent amount of slop between the rear tires when the locker is engaged, we'd say the machining inside the case for the locking pins is very precise. This is a good and bad thing.
It's good the locker is very tight when engaged because no slop or play within the carrier means there can be no sudden loading and unloading on the spider gears, no matter how slight. We'd guess that this diff is as close to an actual spool as you're gonna get in a differentiating carrier, and that speaks volumes for Tera's quality control. However, we found that the extremely close tolerances didn't always allow the locker to engage exactly when we wanted it to.
The way we usually wheel with a selectable locker is to proceed until we lose traction, then engage the locker. However, when we lost traction and hit the dash switch, we sometimes still found ourselves spinning only one rear tire. When this happened, we tried a few tricks like bumping the throttle to vary the tire speed and backing up and rolling forward. However, we ultimately needed to back completely out of the obstacle and make a lazy S-turn before the locker would engage. Subsequently, we began anticipating where our vehicle would lose traction and engaged the locker before we hit that portion of the trail and got our peg leg spinning in the air.
TAG Motorsports's Jay Miller handled the locker install, transferring our carrier bearings from the stock open diff to our T-Locker, setting the backlash, and adjusting the shift fork before plumbing the pneumatic lines from our onboard air tank. The locker can be operated by any pneumatic source that operates at 80-150 psi.
By adjusting our driving habits a little we found the locker engaged every time. We should also note that our testing was performed with very few miles on the unit. We're betting as more trail time is accumulated on the locker, the bores that the hardened pins slide into will wear just enough to allow them to slide more freely inside the carrier.
The T-Locker is a very innovative pneumatic locker that's easy to set up, offers headache-free troubleshooting of the pneumatic system if the need arises, and should prove to be monstrously durable.