Toyota Tacoma
Rear Differential Elocker Actuator Repair

The electric differential locker on my 2002 Tacoma hasn't worked in about two years. Whenever I tried to engage it, the indicator light would just continue to blink and nothing would happen. I finally decided I would try and find out what the problem was. The locker is engaged using an electric actuator at the rear differential. That actuator is controlled by an on-board computer that has interlocks to prevent engagement under unsafe conditions. I was hoping the problem was not in the computer control system as that would make troubleshooting more difficult, at least for me. I began with removal of the actuator assembly.

My truck is a V6, 4WD, 5 spd MT, Xtra Cab with the TRD package. It has 55K original miles on it. Here's what the actuator looks like in place:

The actuator has a shield over it that has to be removed first. The shield is attached in three places. There is a bolt in the center, one on the upper right (which I broke off) and a stud with a nut just to the left of the upper right bolt, in the shadow. Despite what the official Toyota service manual says about one bolt, the actuator assembly is attached in three places. One is with a bolt shown in the lower left. Another is with a stud and nut shown in the lower right. The third is the stud and nut in the shadow mentioned above. There is also the electrical connector that has to be unplugged and a rubber breather hose that also has to be disconnected.

Since I already broke the bolt in the upper right off, I decided to use an acetylene torch to heat the two nuts involved and try to avoid breaking either of the studs off. That worked well. Fortunately, the bolt came loose without breaking. The actuator is then removed from the differential housing, although with some difficulty. I had to pry carefully but firmly both at the top and at the bottom, even after using a liberal amount of PB Blaster at the joint. After working it for a while, it finally came loose.

Here's what I found:

Ugly, isn't it? It seems there is a dead pocket between the actuator and the differential that allows dirt and moisture to collect. Road salt gets in there and just eats away at the aluminum housing. The irregular opening is not supposed to be there. I could see right down into the innards of the actuator. I was discouraged and figured the actuator was junk. I investigated the price of a new replacement at a local Toyota dealer and was surprised to find out the cost would be about $750 just for the part. They don't call 'em stealers for nothing. Well, they can keep it for that price. I don't use the locker much and will do without it before spending that amount. I also checked with an on-line Toyota discount supplier but the price was still way too high at about $550. I would consider $200 but no more.

I looked into a manual cable-type replacement for the actuator but reviews of that aftermarket product were not good. I decided to attempt some kind of repair operation on my existing actuator.

Toyota classifies this product as a non-serviceable item so there are no details of the innards or service instructions in the official service manual. There are some troubleshooting details though. You really should have the official service manual, along with the excellent manual of wiring diagrams when working on any modern Toyotas. They are pricey but needed if you are going to do your own work.

When attempting to power the motor portion, I could see the internal gear operating through the corroded-away opening. However, the actuating gear shown above that mates with the rack in the differential didn't move at all. Even attempting to move that gear with pliers was unsuccessful. It was frozen in place, presumably by aluminum corrosion where the shaft exits the housing cover. The housing cover is held on by two attaching screws. Trying to remove these screws in one piece was a joke since they were frozen in place by corrosion in the threaded holes in the aluminum housing. I decided to just drill them out and use helicoils later. After removing the spring clip shown and the outside gear, I was then able to remove the cover by careful prying in multiple locations around the circumference and using liberal amounts of PB Blaster at the joint. There are two dowel pins in the housing that locate the cover so you need to be careful to do any prying adjacent to them so you don't put any undue bending stress in the cover.

Here's what the inside looks like after the cover (along with the frozen output shaft) is removed:

There is a worm gear (driven by the motor) shown in the upper portion of the housing recess that drives the large gear shown. The large gear is made of a composite material and has been removed from the recess in this photo. All the teeth were in good shape, fortunately. You can also see the three electrical contacts in the bottom of the recess. They ride against the rear of the large gear. The rear of that gear has both metallic and non-metallic areas that, depending on rotary position, make or break electrical continuity between one or more of those three contacts. This arrangement permits the motor to rotate that gear to a certain position and then stop. When a reverse polarity is then applied to the motor, it will rotate in the opposite direction, also to a certain position (where it was originally) and then stop. The yellow material is old grease.

Here's what the rear of the cover looks like:

You will notice a curved section (shown on end) in the upper left between the hook at the end of the spring and a triangular-shaped protrusion near the top. This curved section is rigidly attached to the output shaft. There is a similar curved section attached to the large composite gear that is shown on end in the previous photo. That curved section fits to the outside of the curved section shown in this photo and engages between the spring hook and the triangular piece. The triangular piece is attached to the other end of the spring (covered by the washer shown) by a slot and a hook in the spring. Whenever the large composite gear rotates, it carries the outer curved section attached to the composite gear along with it. In so doing, torque is applied to the output shaft in either direction through the spring. When the large composite gear rotates CW in this view, it moves the triangular piece CW which applies torque to the output shaft via the curved section shown and the spring (hook engages curved section shown here). When the large composite gear rotates CCW in this view, it engages the hook on the spring shown above and carries it CCW. That provides torque to the output shaft via the spring and the triangular piece, which contacts the curved section shown here. This arrangement permits the motor to go full stroke to either stopping position, even when the output gear is prevented from moving at all because the rack cannot engage in the differential due to wheel position. It prevents motor burnout, stripping of gear teeth and blown fuses. As soon as the wheel position permits, the spring will uncoil, move the rack and lock the differential. The same action happens in reverse when unlocking the differential.

I had to use a lot of PB blaster, careful heat from an acetylene torch, and considerable applied torque in both directions to free up the shaft in the cover. It finally got freed up and I could remove it. Here's what it looks like:

I don't know what type of seal that is in the shaft groove. The heat I used destroyed it beyond recognition. I found that a #110 O-ring (nominal 3/8 ID x 9/16 OD x 3/32 W) will work nicely instead. That size is common in those assortments carried by auto parts stores. I got one at the local NAPA store.

Here's the cover after I sandblasted it to clean it up:

I decided to try a fiberglass patch to replace the corroded-away material and seal the cover to prevent dirt, moisture and road salt from getting into the mechanism. This area of the cover provides no real structural integrity so I am hoping it will work. I applied three layers of fiberglass cloth soaked in fiberglass resin.

Here's what it looked like in starting:

Here's what it looked like after the first layer was applied:

And after the third:

Here's what the housing recess looks like after cleaning:

This shows two of the three tapped holes that were drilled out and repaired with helicoil inserts:

Here's what it looks like with the large composite gear and output shaft assembly reinstalled:

The output gear is installed here temporarily for reference purposes. I put the dabs of yellow paint on for my own reference when I started. You can ignore them. There are two slots in that output gear that engage drive tangs on the output shaft. You can see them here at about 3 and 9 o'clock. It is important that they be oriented as indicated with respect to the housing when the motor is energized to go to and stops at the lock position. This verifies correct operation (at the right times) of the contacts below the large composite gear. Shown above is the correct position when the actuator is in the lock position. You can also see in this photo that curved segment attached to the large composite gear that was mentioned previously. There are a couple of different ways to verify the correct assembly, function and position of the output gear with respect to the motor. One is to reinstall the cover, hook up the actuator to the truck's electrical connector, engage the differential lock button on the dash and see if the output gear stops in the location shown. The other way is more complex but can be done at the bench without reinstalling the cover. I decided to use this bench method to verify the assembly before I proceeded. This bench method is described in the manual as a check function but there are some typos there that incorrectly identify some pinouts. I'll address those in the next section.

What you need in order to do a bench verification is a lot of small alligator clips with connecting wires, a 12V battery, and a main heater relay. I used the relay in the truck after pulling it from the relay/fuse panel under the hood. Here's where you find the main heater relay:

The relay is difficult to remove from its socket because of the two nylon retaining clips on opposite sides. I found it easier to remove if you remove the starter relay up above it first to get better access to the retaining clip on that side.

Here's what the test arrangement looks like:

Mess of wires huh? You can see the relay (black and white) on the bench and the actuator in the vise. The 12V battery is behind the vice with the larger alligator clips showing on the battery posts. Do you really need to go to this trouble to check things out? Perhaps not. If the large composite gear, the spring and the output shaft are assembled correctly as shown in the above photos, it should be impossible to install that subassembly improperly into the housing. It shouldn't matter which teeth on the composite gear mesh with the motor-driven worm. The gear should always rotate to the correct position and stop due to the fixed relationship between metallic and non-metallic areas on the underside of the composite gear. For this to be checked however, either the relay mentioned above or the truck's locker ECU must be in the circuit. Otherwise, the three contacts under the composite gear have no function, not being connected to anything, and the motor will just spin around and around without stopping. In any event, I like to verify function as much as possible as soon as possible.

The procedure is explained on page SA-201 of the 2002 Tacoma Factory Service Manual. However, the pinouts shown there for the heater relay do not agree with the pinouts shown on the wiring schematic in the 2002 Tacoma Wiring Diagram Manual. Pins 1 and 2 are the main power connections in the relay as shown on the schematic and not pins 4 and 5 as shown in the service manual. For this procedure, you should interchange pin 1 for pin 5, pin 2 for pin 4, pin 5 for pin 1 and pin 4 for pin 2 on page SA-201 of the service manual. I used the hookup shown on page SA-201 (with the pinout corrections mentioned) for the "Free to Lock" diagram, not the "Lock to Free" diagram. I wanted the actuator to stop in the locked position so I could attach it to the differential in accordance with the service manual instructions.

For those wanting to try this procedure without the manual, here's the corrected pinouts for the main heater relay:

And here's the proper wiring connection diagram for the "Free to Lock" test from page SA-201 of the manual, with the corrected pinouts:

And for the curious, here's the diagram for the "Lock to Free" test, also with the corrected pinouts:

Doing this bench test will verify that the actuator stops in the correct position before final assembly. Remember, when this "Free to Lock" test is done and the motor stops, the alignment of the slots in the output gear must be as shown in the previous photo with respect to the housing.

Once I had the correct assembly and function of the parts verified, I then proceeded to install the actuator cover that I had applied the fiberglass patch to.

The O-ring in the housing that seals the cover was in very poor shape. It's of a size I thought not likely available except on special order from an O-ring supplier, probably with excessive minimum purchase requirements. I decided to just leave it in place and seal the cover to the housing using silicone sealant.

Here's what that looked like before assembly:

Here's the repaired actuator, already for installation on the truck:

Since the actuator is in the locked position, I needed to set up the differential in the locked position in order to correctly install the actuator. I jacked up one rear wheel, and working through the actuator opening with a screwdriver, forced the rack gear to the left into a full locked position. I had to slightly rotate the raised rear wheel to accomplish this. The proper position of the end tooth on the rack is shown in the service manual for installation of the actuator - namely close to the vertical centerline of the actuator opening. Once this was done, the actuator mated up to the differential with no problem whatsoever. Lucky so far. I hooked everything back up and proceeded to the real world test from the dash switch. It works! Locks and unlocks just as it should. I am pleased. I have no idea how the fiberglass patch will hold up over time but will take that as I come to it. For now, it works and I will have to pay attention to periodically engage the thing, even if I don't need it, just to try and keep it from freezing up again.

Rod (NH)
July 2006

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