Installing a 1997 4Runner Electric Locker in a 1985 Toyota 4Runner

Rear Electric Locker

Part 1-Installing the Locker
  By Karl Bellve
Photos by Ken Flesher

There are many options for putting a traction adding device into a Toyota differential. I wanted to have a part time locker that I could deactivate when it wasn't needed due to the amount of snow and ice my truck sees during the winter. There are only two part time lockers available for the Toyota differential. The most popular choice is installing an ARB locker. This is an air activated locker that has proven to be reliable. Another choice is the Toyota electric locking differential. Like the ARB, it acts as a spool when activated. This just mean there is no differential action when the locker is activated and both wheels are forced to rotate at the same speed. The Toyota electric locker uses electricity to switch from an open state to a locked state. It doesn't need electricity to maintain a state but to only switch states. An ARB requires constant air pressure to maintain a locked state. This isn't a big difference but it does mean that the Toyota locking diff will remain locked, even if the wires are torn.  In an emergency, you can also remove the electric motor and manually switch the state of the locker, unlike an ARB. One advantage the ARB has over the Toyota locking differential is speed. The ARB will activate and deactivate much faster, as long as the seals are good. The only real problem with ARBs are that the seals tend to go, causing air leaks and differential fluid to enter the air lines or go past seals. This is rare as far as I can tell and may be due to installer error. The only problem with the Toyota electric locker, besides being slow to switch states, is that the electric motor appears vulnerable to damage. I have used this locker for most of the wheeling season without any damage to the electric motor. So you ask, how do you install an electric locker? Read on...

I first started by talking to Jay Marks Toyota about part numbers and prices. I soon bought a 1997 4Runner  electric locking differential from Jay Marks Toyota with 4.10 gears. This is a V6 differential with 4 spider gears. You can get up to a 4.56 ratio. Other ratios maybe available outside the USA but I can't find those part numbers. The differential included bearings, housing, and the locker, already setup. However, your axle housing has to be modified to fit the differential. It means some grinding, tapping and a small touch of welding. All simplier than having gears setup for a differential. Then, it has to be wired which is covered in part 2 of this article. The locker I bought was meant for an 8.0" axle. This differential will not work for the Tacoma truck since it uses a 8.4" ring gear.

There several things you must do to your original axle housings. Use the electric locking differential gasket as a template to find out what needs to be grinded, drilled and taped. Once you have made these modifications, it might be hard to go back. This picture shows where the modifications are needed. The circles show where 4 new studs holes must be drilled and tapped. This is where the welding comes in. One of the new stud holes resides on a shoulder. This shoulder needs to be flat to make it easier to drill. If you have a drill press, you might not need to do this and eliminate the need for welding. If you do weld, you might want to widen the area that is available for the gasket surface. You have to be very careful to not overheat the housing at this point because you can warp the ring. I also suggest that you drill and tap after you weld, just in case the welding distorts the ring a slight amount. The gasket is not symmetric. Make sure the appropiate side of the gasket is on the diff. Use the differential to figure out which side of the gasket faces the housing. Some people mount the diff and then use long punches to mark the holes on the housing. They say this is more accurate because the gasket may have slight variances.

The very large circle shows the area of the housing that needs to be moved backwards. One of the bolts on the differential comes into close contact in that area. A brass punch should do the trick. The rectanglar areas show the areas that you need to grind metal away from. The way to get the exact location of the stud holes and what metal to grind is by using the gasket that is meant for the electric locking diff. Mark all the locations with the gasket, and drill/grind away. You can compare the two housings here:

I believe that modifying the housing is far simplier than installing a new set of gears. The beauty of this swap is that the gears are already set up! Other then modifying the housing, you just install it like any other differential. Just bolt it on up. The new differential uses 11 studs versus the 10 from the original differential. Also, two of the new studs need to be very long, over 4 inches. You need to purchase some metric ready rod, at M8-1.25. Measure then cut to length.

You might want to do some preventative maintenance while you have the axle shafts out. There are two internal seals that about $4 each and two O rings for the same amount. You can and replace the axle bearings but they need to be pressed out with a SST.

Check Part 2 out where I describe how I wired the locker.

Special thanks to Ken Flesher for his driveway, camera, and his help.
Thanks to Scott Muir for making the modifications to the housing and sending it to me.
Thanks to Jay Marks Toyota for a great deal on the locker.