Most off-road 4x4 projects require a close look at gears and lockers some time in the life of the project. It is the nature of the beast and a VERY important piece that is sometimes overlooked. I have seen others spend thousands of dollars on their 4x4 projects yet still be out on the trail with open diffs and gearing that is way too tall for their over-sized tires. This choice can cause unnecessary wear and tear on their vehicle and on the terrain. A fourwheeler with open diffs is really not much more capable than any 2WD with a traction-aiding differential.

Choosing a Gear Ratio

While we had Project Off-Road Toyota apart for the Total Chaos long travel suspension, we took a close look at our requirements for gearing. We knew we would be installing BFG 33x 10.50 tires so we picked our gearing ratio to accomodate them. Most all stock 4-cylinder Toyotas with 5-speed transmissions came with 4.11 gears and 31" tires. There are some great resources right here on Off-Road.com to help you determine what gears might work best for you.

• Gear Ratio and Tire Chart
• Introduction to Gearing
• Toyota Differential Identification

After reading up on the subject, we decided on 4.56 ring and pinion gearing for Project Off-Road. This ratio will be just slightly lower than stock and should give us just a little more power for turning the larger tires, but still keep the rpm's within reason on the highway to and from school.

For our new gears we contacted Motive Gear. Other reviews and information we found indicated the Motive Gear blue box gear sets are excellent replacement gears and will hold up to any abuse we will be giving them. Motive has a wide selection of gears and bearing sets available for just about any application.

Our front differential, Motive Gear Set, Motive bearing kit, and Detroit True Trac on their way to the shop for installation.

Choosing a Traction Differential

Next we had to pick a traction-aiding differential. Project Off-Road Toyota will not be a serious rock crawler - it will see significant amount of time on the street. This alone eliminated several of the choices. A Detroit locker is just not a good choice on the street and especially when a fair amount of the driving will be on snow and ice covered roads. We felt that our requirements also eliminated manually-activated full lockers. We would require some kind of limited-slip differential.

We felt that this left us with one obvious choice for our project - The Detroit TrueTrac differential. The Detroit TrueTrac is the only limited-slip differential that does not use clutches or friction plates that wear out or require adjustment. Since it is all mechanical, no special additives or lubes are required. The Detroit TrueTrac is an excellent choice for both front and rear because it will automatically split the torque without creating steering problems. In normal driving the TrueTrac functions like an open diff but when hitting slippery or low traction conditions it will limit the amount of wheel spin. This means no extra tire wear but additional grip when I need it.

There is one catch with a TrueTrac. It requires "some" resistance to transfer torque to the other tire. This means that if you have one tire completely in the air, the TrueTrac may not transfer torque to the tire that does have traction. Luckily there is a work-around. This requires the driver to use some braking to force the diff to transfer the torque to the tire that is slipping. We plan on spending more time in low traction situations than in situations where we have one wheel hung in the air, so we didn't feel this counted out any of the other benefits of the TrueTrac.

Installation

While we had our front differential out for the Total Chaos Long Travel suspension install, we took the front differential and parts to a local shop for install at the same time. We followed that up later with the rear differential after we had the front suspension installed. This allowed us to drive the truck down to the shop for the rear differential installation. You should expect to pay $250-$500 per diff for installation.

How does it work?

Until we get a little farther along with Project Off-Road Toyota, we won't be able to answer how well it works. Previous experience on other rigs have shown us that this combination will work excellent on and off road. We will report back in a later stage of the Project.

Sources:

Motive Gear
Toll Free Number: 1-800-934-2727
1001 West Exchange Ave.
Chicago, IL. 60609
Local Ph. 1-773-247-3400.
Toll Free Fax 1-800-526-4885.
Local Fax 1-773-579-3788