Ultimate Toyota-Based Axles: Part 1
Published by Trails Less Traveled on October 4th, 2004
We’ve been working with various manufacturers and collecting parts for the last six months to assemble the ultimate Toyota-based rear axle. The stock axle housing will be discarded and our rebuilt Tacoma third-member loaded with 5.29 gears and an ARB Air Locker is getting reinstalled in a custom-fabricated Tundra-width housing from Front Range Off-Road Fabrication. We’re also using a full-floating axle conversion kit from FROR along with 4340 Chrom-Moly 30-spline full-floating axle shafts from Superior Axle & Gear. All of the fabrication and installation work is being performed by WFO Concepts in Auburn, CA.
GEAR & LOCKER SELECTION
We always planned to run 35” tires on the TLT long-travel Tacoma, but could hardly even drive the truck with 33×10.5” tires and 3.58:1 gears. Many Tacoma trucks come with 4.10 gears, which can turn 33” tires, but 4.56’s or 4.88’s would be ideal. Since tire diameter should help to determine the ring & pinion gear ratio that is selected, we mounted a set of 35” tires to start check for firewall clearance. The tires fit and we selected a 5.29 gear ratio to help get the rpm’s up into the powerband of our high-winding 2.7L (3RZ) 4-cylinder engine and compensate for the lack of bottom-end torque. CLICK HERE to view the tire diameter/gear ratio/RPM chart. We contacted Superior Axle & Gear to order a set of ring & pinion gears for the front and rear of our Tacoma because they manufacture some of the highest quality axle shafts and ring & pinion gear-sets on the market.
We knew that a selectable locker in the rear axle would provide the traction that we needed in the desert and the mountains without compromising the vehicle’s on-road handling, but our base-model SX Tacoma didn’t come equipped from the factory with an electric locker. Unfortunately, the TRD locker cannot be easily retrofitted to a non-TRD Tacoma because it uses an entirely different bolt pattern and axle housing. We looked into swapping out our entire rear axle for a TRD unit and discovered several things in the process that made us reconsider.
The special TRD third member is based on the old Toyota 8” V6 differential, while our non-TRD rear axle has the same third member that is used on all of the T100 and Tundra trucks. The Tacoma/T100/Tundra model has several upgrades from the older 8” including a larger pinion shank diameter and main-bearing cap girdle (see above picture), which reduces deflection (deflection is a leading cause of ring & pinion failure). The rest of the axle assemblies are very similar. TRD and non-TRD Tacoma axles both use 30-spline axle shafts, which are interchangeable between models.
After evaluating all of our options (see Gearing Introduction article for more info.), we purchased an ARB air-locker for our non-TRD rear axle and an ARB air compressor. We chose to run an ARB setup because of their worldwide reputation as unfailing trail-worthy differentials. The strength of the ARB is comparable to any mechanical locker for our application and it is much more versatile. To see an animation of how an ARB air-locker works, CLICK HERE
We’ve heard people argue that the switches and the air supply lines or electric motors used to actuate selectable lockers are prone to failure and exposed to damage. While it’s true that the electric motor on the TRD locker is somewhat exposed, it’s hard to say that properly routed ARB air-lines are any more vulnerable than brake lines. Engines, transmissions and axles along with electrical systems, switches, hoses and compressors can all fail. But when quality components are properly installed and maintained, they can provide years of trouble-free service.
We decided not to install a locker up front because even though an ARB would be much stronger than the stock carrier, we are concerned about the (lack of) strength in the 26/27-spline CV axles and hi-pinion 7.5” front differential. A locker can provide more traction than the drivetrain is capable of handling, which leads to broken parts. We’re hoping that an open differential will limit traction just enough to keep us out of trouble, although it’s still possible to stress the front drive-train components by using too much momentum and wheel-spin to make up for the open differential. We’ll just have to drive smart.
WFO Concepts was Founded by brothers Trevor and Beau Huiskens shortly after graduating from college at Chico State University. They relocated about an hour south to Auburn and opened up shop. The Huiskens have been working on trucks their whole lives and that’s clearly evidenced by the quality of work that they’re turning out. We drove out to their shop all the way from Santa Cruz (3hrs) to have them install our gears and rear locker. For anyone in the California bay area, WFO’s reasonable labor rates and service more than make up for the gas burned to get there. In addition to their fabrication and general mechanic services, they have a developing line of performance off-road products.
We chose to use an ARB air compressor because it is one of the smallest/most compact units available and it will only be used to power the air locker. It is capable of inflating tires, but anyone planning to air-up after each trail run should look into some of the alternatives like the PowerTank C02 system. The ARB compressor comes with a wiring harness that makes for an incredibly easy installation. Just plug-in the pre-terminated connections, run power leads to the battery and mount the switches.
The ARB wring harness comes in two pieces. The compressor wiring harness passes through the firewall and into the cab, where it plugs into the end of the harness with the compressor and locker switches. This image shows the end of the compressor end of harness where it plugs into the other half of the harness. The junction does not come installed so that it can pass easily through the firewall.
We determined that the best place to bring the harness into the cab was through the parking-brake cable grommet. It is near the floor, next to the gas pedal. We inserted the blade terminals one at a time, and then pulled the harness through. Zip-tie it to keep it out of the way of moving parts like the gas pedal.
We mounted the two switches side-by-side, next to the ignition key in an unused area where the digital clock would be on an SR5 Tacoma. ARB switches can easily be mounted into any flat surface or unused accessory panels with minimal modification. If we decide to add a front locker in the future, we’ll just move the compressor switch to the accessory panel next to the hazard switch in the picture on the right.
The ARB air compressor has three ports. The center port is for the pressure-switch that maintains a specified pressure range when the compressor is turned on. The compressor doesn’t run longer than is needed to restore the specified pressure to the system. The two ports on either side of the pressure switch port are for the lines that connect to the electronically operated air locker solenoids.
We chose to mount the compressor in the rear of the truck for better weight distribution (and the front inner-fenders will probably be removed eventually anyway). There is still enough clearance for a 35” spare tire (pictured), and we’re planning to build a sheet-metal splash-guard to protect it from dirt and rocks.
Wiring the ARB compressor is about as simple as it gets. All of the connections are labeled and pre-terminated. Once the ARB air-locker is installed, run the light blue air-line (pictured far left) from the electric solenoid to the differential. Routing and cutting and installing the air-line is covered in the last step of the rear differential installation below.
Like older IFS Toyota’s, The Tacoma uses a 27 spline, 7.5” front differential. But unlike the older model trucks, the Tacoma uses a hi-pinion differential. Hi-pinion (above centerline) axles are ideal in front applications because they provide a substantial increase in strength compared to a traditional front-mounted low-pinion (below centerline) axle. This is because hi-pinion axles use reverse-cut gears. The name “reverse-cut” indicates that the sides of the gears teeth are cut the opposite of standard gears, what is normally the coast and the drive side is reversed. Hi-pinion differentials are often erroneously referred to as being reverse-rotation. Although the gears are cut opposite to standard gears, they still rotate the same direction. This makes for proper gear engagement resulting in as much as a 15-30% increase in strength.
We removed the front differential assembly before bringing it to WFO in order to speed up the installation. These are NOT intended to be step-by-step articles explaining how to set up ring & pinion gears. We only mean to provide an overview of the parts and process involved.
The guys at WFO began by taking the front housing apart. In this image the intermediate shaft and axle housing from the passenger side of the front differential assembly have been removed, leaving only half of the ‘clamshell’ intact. Notice the safety tabs that keep the ring gear bolts from coming loose.
WFO installed new bearing on the factory carrier since we didn’t install a front locker. The old carrier bearings are shown being removed and then the new bearings that come with Superior master overhaul kit were pressed onto the carrier. The pinion bearings and all of the seals were also replaced.
Grease paint is applied to the ring gear to check the pattern. Achieving a good wear-pattern on the drive and coast sides of the ring-gear is critical to the long-term performance of any gear-set. A poor wear-pattern can be noisy and cause accelerated ring & pinion wear. Checking the pattern on this type of front differential can require assembling and disassembling the whole clamshell case several times to inspect the pattern and make adjustments. Since we reused the stock carrier, we were also able to reuse the same carrier shims, only re-shimming from side-to-side to adjust the backlash. After WFO was satisfied with the pattern and backlash, we reassembled the differential and reinstalled the front differential in the truck.
We couldn’t remove the third member from our rear axle ahead of time since we drove the truck out to WFO’s shop, but it only takes a few minutes to complete this step. The axle-shafts must be slid out a few inches until they are disengaged from the carrier splines so that the third member can be removed. The parking-brake cables have to be disconnected and there are only four nuts need to be removed from each side of the axle housing.
WFO created this custom bench-top fixture for gear installations. Each side of the cube holds a different third member (Toyota 8”, Ford 9”, etc.). They removed the main bearing caps and the ring gear/carrier dropped right out.
After the pinion is removed, the bearing races can be removed before cleaning the empty third member. WFO dropped our third member into their hot tank before re-installing the differential. It came out looking clean-as-new.
Trevor set the new outer pinion race and pinion seal that were supplied in the Superior master-install kit. One important point to make is that new carrier shims are not included, although they will be required during the installation. Replacement shims are available through Toyota in various thicknesses, but they are special-order only and it’s hard to know exactly what shims will be needed before getting started. Luckily, WFO had a variety of shims in stock. We actually ended up using ARB carrier shims for a Dana 44 application to get our carrier shimmed correctly.
We also used the new pinion crush-sleeve included with the Superior master-install kit. A solid ‘crush-sleeve eliminator’ does NOT provide any real advantage over a crush-sleeve. No impact to the driveshaft or pinion flange could cause the crush-sleeve to crush any further or develop excessive play between the pinion bearings.
The new ring-gear was heated and then installed onto the carrier. Make SURE that thread-locking compound is used on all of the ring-gear bolts! Otherwise the bolts can fall out and rattle around in the differential until they destroy your expensive new ring, pinion and carrier.
After the pinion and carrier are installed, a magnetic-base dial indicator is used to measure the backlash. On the second try, Trevor nailed it perfectly. These images show the great wear-pattern that WFO achieved on the drive and coast dies of the ring-gear. Trevor routed the copper air-line to the hole in the differential housing and cut the line to length. The compression-nut and the compression-bushing slid right over the line and then the nut was threaded onto the bulkhead fitting in the differential housing.
The third member was reinstalled in the housing and then we ran the flexible blue air-line from the differential to the switch/solenoid mounted to the compressor. We always try to route flexible hoses together so that they are less exposed and vulnerable. The ARB line, flexible brake line and extended breather-hose were all zip-tied together and routed to the driver’s-side frame-rail.
First, we secured one end of the air-line to the switch/solenoid, which is a simple push-lock connection. All you have to do it press down on the orange flange (pictured above right), insert the air-line and then release the flange. Then we ran the length of tubing alongside the flexible brake line to the differential bulkhead. Then we carefully cut the air-line to the proper length, using a razor-blade to make sure not to crimp the line and secured it to another push-lock fitting.
With the ignition turned to Accessory (electrical power but engine not running) and the rear wheels raised off the ground (with the vehicle supported on jack-stands), we tested the locker and compressor for proper operation by spinning one of the rear wheels by hand. The rear wheels should spin in opposite directions when the ARB air-locker is unlocked and the same direction when it’s locked.
The 5.29:1 Superior gears made all the difference in the world, especially in low-end acceleration. Our Tacoma is now much livelier and fun to drive in all gears. Although we now run slightly higher RPM’s on the freeway, we feel it’s well worth it for the improved performance off-road. The ARB air-locker allows us to take the Tacoma places we would have never been able to go with an open differential and it’s 100% transparent on-road. The combination of more aggressive gearing and greatly improved traction has made a night and day improvement in the overall performance of the truck in all situations. Our fuel economy has actually improved too, since we can finally use 5th gear again and the engine is no longer lugging at low RPM’s.
This Article was originally published on Off-Road.com November 2004
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