Technical Articles Relating To Off-Road Vehicle Development

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Ultimate Toyota-Based Axles: Part 3

Published by Trails Less Traveled on April 5th, 2005

 

Animation of full-floating hub assembly

INTRODUCTION

We started off this series of articles by covering the fundamentals of differentials and gearing. In Part 1 of the Ultimate Toyota-Based Axle buildup, WFO Concepts assembled our non-TRD Tacoma/T100/Tundra third member with an ARB air locker and Superior 5.29:1 ring and pinion gears. In part 2, we toured the Superior facility with Mike Denton, jr. and he showed us all of the steps involved in manufacturing custom axles, like the 4340 full-floating axle-shafts they built for us. This installment will focus on the features of our new custom axle housing, built by Diamond Axles and a full floating conversion kit manufactured by Front Range Off Road. Before we look at these products in detail, let’s review the differences between semi-floating and full-floating axles.

SEMI-FLOATING AXLE

Semi-floating axleMost cars and trucks on the road with solid rear axles use semi-floating axle-shafts. In this simple and cost-effective design, the axle-shafts support the weight of the vehicle in addition to providing the driving force to the wheels/tires. Semi-floating axles just aren’t the best choice for any vehicle that carries heavy loads or is driven hard off-road. A slightly bent axle-shaft will cause the axle seals to fail prematurely, allowing oil to seep past the wheel bearings, contaminating the drum brakes and rendering them useless. A broken axle-shaft can result in more serious damage if the wheel/tire separates from the vehicle when the axle-shaft fails.

FULL-FLOATING AXLE

Transparent image of hub assemblyThis transparent image of our full-floating assembly is intended to illustrate the knee-bone-connected-to-the-shin-bone relationship of the components in a typical ‘full-floater’ setup. The axle-shaft turns the drive-flange (not pictured) that is bolted to the hub. The hub rotates on the spindle, which is mounted to the axle-housing using FROR’s adapter plate. The axle housing carries the vertical load and the axle-shaft is only used to provide power to the wheels.

Full-floating axles use two sets of tapered wheel bearings per wheel, mounted in tension, to distribute vertical and lateral loads. Full-floating wheel-bearings are typically much larger in diameter because they ride on the spindle instead of inside the axle housing. In contrast, semi-floating axles use a single wheel bearing per wheel, pressed onto the axle-shaft, and the whole assembly is bolted into the axle housing together. For reference, all steering 4WD front axles are ‘full-floaters’ because the wheel/hub has to ride on a spindle that is able to turn/steer.

Full-floating axles are superior to semi-floating axles. It’s a better design, plain and simple.

AXLE HOUSING

Animation of axle housingDiamond Axles recently introduced a complete line of axle-housings designed specifically for off-road use. These fabricated housings can be custom-made to accommodate standard Toyota 8” center-sections, as well as TRD electric-locking differentials and non-TRD Tacoma/T100/Tundra third members. A heavy-duty Ford 9” version is also available.

Center section of housingWe decided to order a 66” wide non-TRD Tacoma/T100/Tundra housing for our Ultimate Toyota-Based Rear Axle Build-Up. A stock Tacoma’s rear axle width is 60” (wheel-mounting-surface to wheel-mounting-surface), but we wanted to match the track-width of a stock Tundra/T100’s rear axle because our front axle width is 67” (the same width as a Tundra front end).

Housing endStock Toyota axle housings DO bend frequently when subjected to hard use off-road. The additional strength and custom widths available from Diamond Axles made our decision to order a new axle housing easier. Our new housing uses massive 3-1/2” diameter DOM axle tubes with .375” wall thickness vs. the stock Toyota housing at 3” diameter x approximately .188” wall thickness. Ground clearance is also improved by 3/4” and is slightly more on some models. The new Diamond Axle weighs in at about 80lbs, compared to 45lbs for a similar width stock Toyota housing. Housings can be ordered with 3, 3-1/8 or 3-1/4” diameter tubing with any wall thickness to tailor the strength/weight for specific applications.

FULL-FLOATING CONVERSION

Complete FROR FF kitFront Range Off Road has developed a bolt-on full-floater kit that fits all four-wheel drive Toyota rear axles and upgrades the rear axle to disc brakes at the same time. The kit consists of a set of custom full-floating axle-shafts, machined steel spindle adapters with disc brake tabs and all necessary hardware/seals. The kit is designed to maintain stock track-width, so tire-to-body clearances will not be affected.

If you have any reservations about a ‘bolt-on’ full-floater kit, read on. We had some doubts too, until we talked to Brian at FROR. He reminded us that bolt-on spindles have been used on all types of front axles in exactly the same way without incident. These Toyota front hubs and spindles are clearly stronger than the stock Toyota semi-floating rear axles and the splines at the drive flanges/locking hubs are 1.3” diameter x 30-spline, just like the inner axle-shaft splines at the carrier.

Machined flangeThis custom-machined adapter ring is the component at the center of the FROR full-floater conversion. The adapter bolts to the axle housing with the included studs and locknuts. There is a tolerance-fit indexing ring machined into the adapter that mates to a male register on the axle housing so that vertical loads are not transferred to the mounting hardware.

The hubs and spindles, as well as the disc brake rotors and calipers, can be sourced from any ‘81-85 4×4 Toyota pickup. These parts are strong, reliable, inexpensive and readily available. If you want to keep the parking-brake, the rear calipers from a 79-81 Toyota Supra can also be used with this kit. We are planning to adapt a pair of Tacoma 4-piston front disc calipers and rotors to our rear axle, so we ordered it without any brake mounts. Larger Tundra rotors and calipers will probably replace our stock front brakes to maintain some brake bias. Any time the rear brakes are modified, a manual proportioning valve should also be used in place of the factory LSPV (load sensing proportioning valve).

We ordered two complete hub and spindle assemblies from Yota Yard in Denver, CO. They’ve got the best selection and largest inventory of any Toyota-specific truck wrecker we’ve ever used.

ASSEMBLY

Housing endFlange installedSnout installed on flangeThis is the stock Toyota housing end, stripped bare and ready for assembly. The machined adapter bolts directly to the axle housing, using the supplied hardware. The spindle will only bolt onto the adapter in one orientation, so make sure the adapter is indexed properly, so that the spindle can be installed with the drain slot pointed down. This will prevent water from getting trapped between the snout and the flange. Install the spindle onto the adapter ring using the factory hardware.

Hub mounted to flangeNext the hub assembly slides onto the spindle. It’s advisable to install new bearings and seals at this time. The hub fastens to the spindle using factory hardware. We’re going to have to do some machining to these hubs in order to use the stock Tacoma rotors which slip OVER the hub and wheel-studs instead of using the stock rotors that are mounted to the backside of the hub. Although this makes for some more work up front, changing rotors will be simpler than the OE design (the rotors are held on by two bolts and the wheel-studs are then pressed through the rotor and hub).

Axle shaft installedHub lock-out installedThe axle-shaft slides inside the snout and engages the differential at the center section. The locking-hub body slides over the axle-shaft. We don’t have a picture of the locking hubs installed because we are planning to use custom drive flanges instead. FROR sells a high-strength 12-point ARP stud conversion kit for the locking hubs. Hendrix Motorsports is also capable of performing a 6-pin upgrade for added shear strength. The stock outer hub assembly only has a 2-pin interface, which has on occasion been known to shear under heavy off-road use, Hendrix machines the stock components to accept 6 pins.

CONCLUSION

There are many examples of semi-floating axles that have performed well in all types of vehicles, including some that are used HARD off-road. If full-floating axles aren’t in the budget, check out the 4340 semi-floating Toyota axle-shafts from Poly Performance. If you’re interested in using the best components available to build a Toyota-based rear axle that is easy to build, install and find parts for, FROR’s full-floater kit is well-worth the money.

In the next installment, we’ll fabricate and install the disc caliper mounts and new lower shock mounts. We should be ready to prep the new axle assembly for final installation.

This Article was originally published on Off-Road.com April 2005

Links to other articles in the Ultimate Toyota-based Axle build-up:

Introduction to Gearing
Part 1: Gearing and Locker Selection
Part 2: Manufacturing Axleshafts

 

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