There are essentially two types of differential locks; one type is fully automatic, engaging whenever wheel slip is detected and the other is selectable, requiring the driver to engage the differential lock. The fully automatic type affect the drivability of the vehicle on the pavement whereas selectable are transparent until engaged.
After driving several vehicles with automatic lockers, I quickly determined that these units are not for me due to the on-road performance. This left me with two options for selectable differential lockers--the ARB air locker or a Toyota electric locker from a 1996+ 4Runner or Tacoma TRD. The ARB is a very respected locker, however they require very careful installation otherwise air leaks develop. These units run $650 plus require an air source, which generally costs around $200. I like the simplicity of the Toyota locker and I like using factory stuff. This set-up cost me approximately 1/3 the cost of the ARB, which influenced my final decision to use the Toyota locker.
A full write up on how to install a Toyota electric locking differential into a pre-1996 vehicle is located here.
I am fortunate to have a friend that has the tools and knowledge required to take-on a project like this. I had never done work like this before...the entire rear axle had to come out of the vehicle, the axle housing required grinding, drilling, tapping and welding to accommodate the new differential carrier, none of which would have been possible without my friend.
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Rear axle removed from truck.
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Lookin' kinda naked under there... |
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The first step was to clean up the housing, drill and tap four holes for the new axle studs, cut the C-shaped notch to accommodate the diff lock shift fork and add a bead of weld around the two longer studs to provide more surface area for the gasket to seal. Shown here is the completed housing. |
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This photo, taken from the locker retrofit article, illustrates the modifications necessary on a 4 cylinder differential housing. The yellow circle inside the housing represents the need to dent the housing outward to provide clearance for a bolt on the back of the differential carrier. The red squares at the top and bottom show the amount of material that should be removed to accommodate the ring gear. Much to my delight, these modifications were not necessary on my V6 rear. Apparently there are some differences between 4 cylinder and V6 housings. |
| These photos illustrate the amount of clearance between the protruding bolt and the V6 housing: | |
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A bead of weld was added around the new axle studs to provide a larger surface area for the gasket to seal. |
The differential carrier to be installed in my truck came from a wrecked 1998 Toyota 4Runner with a 4.30 gear ratio. My truck came from the factory with 4.56. Luckily, my friend has experience re-gearing differentials. On basically his first try, he had the 4.56s installed with 0.006" backlash--right in the middle of factory specs at 0.005-0.007".
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On the left, the stock 1994 open differential carrier.
On the right, the 1998 electric-locking differential carrier.
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| The housing gasket and hi-temp RTV sealant was added to the housing and the differential carrier was bolted-up. The whole axle assembly was then reinstalled in the vehicle. This is the final product: | ||
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There are six wires that run from the cabin to the rear-end. Two of these wires provide positive power to the motor, two control the motor's limit switches, one sends power to the dashboard LED when the diff is in the locked state and one ground wire. The electronic control unit (ECU) requires a power source, ground and a lead going to the dashboard switch. I left two wires unplugged; one wire should go to the speedometer so the locker will not lock at speeds above 5 MPH and the other should go to the 4WD selector so-as to not allow locker engagement unless in 4WD-Low. I am not sure whether or not the speedometer in my 1994 truck works identically to those in the newer ones, so I didn't even bother trying to hook this up. The older trucks like mine do not have a 4WD-Low indicator switch, so I hooked up a safety toggle switch under my dashboard so the switch has to be in the "on" position for the dash diff lock switch to do anything. I did primarily to act as a safety so that someone did not accidentally hit the dashboard diff lock switch while traveling down the highway at 75 MPH.
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I chose to use the factory diff lock switch with a green LED to indicate when the diff lock is in the 'locked' state. |
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| To simplify wiring, I chose to use the factory computer (really just a box with two relays) to control the diff lock. I used velcro to attach it to the power antenna relay above the pedal assembly. |
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| This was the first e-locker retrofit that utilized all factory electronics (at least as far as I know). As such, I spent a great deal of time studying the factory service manual (FSM) wiring schematics trying to understand how the system worked. If you find this diagram helpful, please let me know. |
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This locker works very well. If the splines inside the differential are lined-up, it will lock in less than one second. If the splines are not aligned, either the slightest forward momentum or any amount of wheelspin will turn the sidegears and the differential will lock. It seems to take a little longer for the differential to unlock. I found that the differential will remain locked for some time if driving in a dead-straight line. Give the steering wheel the slightest jerk, thereby turning the sidegears to align the splines, and it will unlock.
I highly recommend using the Toyota e-locker if you or a friend are capable of doing the housing modifications.
