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Toyota Tacoma Locker Upgrade

Posted in How To: Transmission Drivetrain on November 16, 2016
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This 1996 Tacoma was gutless when we got it, and we initially blamed the four-cylinder engine. After a friend from Slee Off Road recommended that we take a look at the ID plate under the hood, we realized that the culprit was the 3.58 axle gears. Those weren’t even up to the task of pushing the puny stock tires down the road, and we made matters worse by adding larger knobby tires (we can’t help ourselves). We knew that we had to regear the axles, and while we were in there we might as well add a locking differential (again, we can’t help ourselves).

Then we got the idea of swapping in a selectable electric locker that came from the factory on TRD-model Tacomas. The entire axle assembly cost less from a junkyard than an automatic locker, much less a selectable locker. We ordered 4.56 Nitro gears and installation kits from JT Parts with the money we saved, and took the whole thing to Bayshore Truck for the installation. Pulling the differentials ourselves got some grease under our nails, but by doing the easy part ourselves we only had to pay Bayshore for its specialized knowledge of setting up gears.

The result is a truck that is more responsive and fun on the road, where it spends most of its time. We even saw a small increase in fuel mileage by allowing the engine to operate in the most efficient part of the powerband. Off-road we gained capability, and with the selectable nature of the electric locker there are no odd handling quirks or accelerated tire wear on the pavement. While our four-cylinder Tacoma is no rocket ship, the improvements made with the lower gears and selectable locker were well worth the effort.

We started with a complete TRD rear axle assembly that we sourced from a junkyard. The electric locker is easy to identify due to the solenoid on the side of the third member that moves the shift fork.
Non-TRD Tacomas, even our base model four-cylinder truck, actually use a stronger 8.4-inch rearend that has girdles to tie in the bearing caps and uses carrier bearing shims instead of spanners. We knew that we were taking a step backwards in strength but felt that the 8-inch differential was strong enough for our lightweight camping rig.
Aaron Lechner at Bayshore started by disassembling the donor axle and putting the whole thing in their industrial parts washer. Cleanliness is key when dealing with gears, bearings, and seals to ensure a long service life.
Nitro Toyota ring-and-pinion sets use 29-spline pinions, unlike most gears that use the older Toyota 27-spline pinion. This did require a new pinion flange, but the Nitro triple-drilled flange ensured that we had no issues matching the pattern on the pinion to our driveline.
Nitro Axle & Gear installation kits come with high-quality Koyo bearings along with shims, a new pinion nut, ring gear bolts, and marking compound. We used a crush sleeve, but Nitro also offers solid spacers for those who prefer them.
Lechner laps each ring gear and pinion with an abrasive disc before installation. This small step helps gears run cool and quiet and is just one of the little details that sets Bayshore apart from most gear shops.
Remember to use thread-locking compound on the fasteners when reassembling the differential. These are for the case of our electric locker, but Lechner also put thread-locking compound on the ring gear bolts prior to torqueing them to 70 lb-ft.
The Toyota electric locker uses an electric motor and worm drive assembly to engage or disengage the locker via a shift fork and collar. Lechner explained that this configuration is very similar to what is used in the large over-the-road trucks that Bayshore often services. Should the Toyota wiring ever fail, it is possible to remove the electric motor and manually lock the axle to get off the trail.
Backlash for the 8-inch axle should be between 0.006 and 0.010 inch. You can see the spanners that allow easy adjustments during gear setup. This, combined with the ability to put the third member on a bench (unlike a Dana axle assembly), makes the Toyota 8-inch one of the easiest differentials to set up.
The TRD rear axle bolted right in place of our factory 8.4-inch rear axle. We got the donor axle complete with brake lines so all we had to do was connect the soft line that drops down from the frame and tighten up the U-bolts and the axle was in.
Toyota used different mounting patterns on its drivelines over the years. Nitro takes the guesswork out of bolting your factory driveline up to your newly geared rearend by offering flanges that are drilled for the three most popular Toyota bolt patterns. This made things easy.
Once exception to the “bolt-in” installation was the difference in parking brake cable location. On the new axle it was below the leaf springs, while the factory parking brake cable was above the leaf springs. This change took place in 2003, but we can use our old axleshafts in the new housing to connect the factory parking brake cable. Both 8- and 8.4-inch axles use 30-spline axleshafts of the same length.
The electric locker needs power in order to move the solenoid that engages and disengages the locker via the shift fork. The factory wiring has numerous relays and is expensive to purchase new from the dealer. CJK Offroad has an alternative that uses a momentary switch to activate the locker.
The CJK Offroad harness uses factory Toyota plugs to fit directly in the electric locker solenoid. The wiring itself is wrapped in a sleeve to keep the wires from getting abraded. We routed the wiring up along the rear brake line and then along the inside of the frame to the cab.
The CJK Offroad harness includes a toggle switch that looks right at home in the interior of our Tacoma. Starting with a bare-bones truck meant that there were plenty of unused panels on the dash. You just hold the switch up a few seconds to engage the locker and hold it down for a few seconds when you want to disengage it.
The front differential in our Tacoma uses a clamshell housing with a 7 1/2-inch ring gear. The skidplate, brakes, hubs, knuckles, and CV axles must be removed in order to access the front differential and remove it from the vehicle.
These circlips hold the CV axles in place where the splines slip into the differential. If they are crushed or damaged they should be replaced before the CV axles are reinstalled. Fortunately ours were in fair condition.
Rather than go through the trouble of reassembling the entire front clamshell axle to check the backlash, Lechner instead put the differential and case into a press where he could simulate the assembled housing while still easily checking the gear setup. Once he was happy with the results he buttoned the front end back up.
The new 4.56 gearset uses nine teeth on the pinion and 41 on the ring gear. The original 3.58 gearset used 12 and 43, respectively. The lower (numerically higher) gear ratio is slightly weaker since less teeth are in contact at any given time, but that was a price we were willing to pay to get our acceleration back.
After applying thread-locking compound, Lechner torqued the ring gear bolts on to the carrier at 70 lb-ft using a torque wrench rather than an air gun. All of the torque specifications between the 8-inch rear differential and 7 1/2-inch IFS front differential are shared, which simplifies the process.
Lechner uses anaerobic sealer on the pinion nut before installing it. Once the nut is torqued to 15 lb-ft the air is cut off from the sealer, creating a gasket on the pinion nut to prevent any possible leaking.
The goal of setting up a ring-and-pinion is for it to be strong, dependable, and quiet. This is achieved by putting the contact between the ring-and-pinion in the center of each tooth, both in terms of the root and crown (up and down) and the heal and toe (inside and outside) of the gear.
After the installation we broke in the gears, which involves only driving short distances and avoiding heavy loads at first to heat-cycle the gear. After changing the fluid we headed to the Colorado backcountry, where we put our new gears and locking differential to good use.

Did We Save Money?
On our trip to Colorado, we were underwhelmed by the power of our regeared truck. Initially we thought that the issue was the heavy load we were carrying. Then after removing the weight from the bed we blamed the elevation. Upon closer inspection we found that the rear tires were feathered after only 1,000 miles. Some measurements revealed a severely bent rear axle that was scrubbing tires down the road. We should have noticed this when the axleshafts were so hard to get into the housing. A call to Slee Off Road got us a new housing, and we transferred over all of our components, but we didn’t accomplish our goal of adding a selectable locker for cheap. Next time we go to the wrecking yard we will remember to measure twice, buy once.

Sources

JT's Parts And Accessories
Cashmere, WA 98815
509-293-4174
www.justdifferentials.com
Nitro Gear & Axle
Sacramento, CA
916-673-6464
www.nitro-gear.com
Slee Off-Road
888-494-7533
www.sleeoffroad.com
Bayshore Truck Equipment Co.
775-331-6605
http://www.bayshoretruck.com
CJK Offroad
281-639-8597
http://cjkoffroad.com/

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