Vehicle Running Gear

Tom Sheppard's Four-by-Four Driving, 5th Edition


Can you learn to be a better 4x4 driver from a book?

The answer is yes. And no.

Don’t stop reading, because that’s not an evasion. 

The “no” part of the answer is easy to explain. Simply put, nothing can substitute for having an experienced human instructor in the seat next to you, or outside your open window, to give you second-by-second advice on your control inputs and choice of lines. Not long ago I watched Tim Hüber stand next the the driver’s window of a Range Rover while he had the owner repeatedly back up and slowly inch over a soccer-ball-sized boulder. Back and forth, back and forth. The aim was to hone the driver’s ability to gently ease over an obstacle or down a ledge, rather than bouncing and compressing the suspension, which reduces ground clearance and increases the chances of contacting bodywork. The fellow finally nailed it, and negotiated the following driving course with consummate grace. I can think of dozens of other instances I’ve watched (or, indeed, have experienced as a student), with such skilled and patient instructors as Sarah Batten, Graham Jackson, or any of the ex-Camel Trophy team members who’ve taught at the Overland Expo for a decade now. 

Having a live instructor is especially vital when learning to drive in conditions new to you, or more extreme than you’ve experienced before. This applies to such procedures as driving on side slopes, negotiating steep hill descents or difficult climbs, and similar situations where inexperience might either make you overconfident (unlikely), or too timid to fully exploit the capabilities of your vehicle.

However. You can significantly enhance your level of preparedness for that personal instruction by reading the right book. And I know of none better than Tom Sheppard’s Four-by-Four Driving. I’ll offer full disclosure right now: I wrote the chapter on winches and winching, and the section on the Hi-Lift jack, for this and the previous edition. But that’s a fraction of what this book is about.

(And in case you think you’re beyond such a primer, note that Four-by-Four Driving is the mandatory textbook for several trainers I know who contract with two governments to teach Special Forces operators advanced driving and recovery techniques.) 

Why is it so good? I think the answer lies largely in the fact that Sheppard was a test pilot in the RAF before he took to solo exploration of the Sahara. And when you’re flying an experimental jet aircraft, poor preparation and bad driving won’t just get you stuck—it will get you killed. Thus Tom insists that a thorough knowledge of the vehicle itself, and especially its driveline and four-wheel-drive system, is the key to being an effective driver. Think of it in terms of a maxim:

If you don’t know how the vehicle operates, you won’t be able to operate the vehicle. The more you know about how it operates, the more effective an operator you will be.

For this reason, a full 20 percent of Four-by-Four Driving is devoted to an exhaustive look into the drivetrains and systems of vehicles from the Suzuki Jimny up to and including the Bentley Bentayga. While you might be tempted to find your own model in here and only read about that, don’t. Learning about other approaches will help you understand both the strengths and weaknesses of your own ride. Besides, if you ever have the opportunity—or need—to drive something foreign to you, you’ll look like a hero if you hop in and immediately turn that LR4’s Terrain Response dial to the proper setting—or, for that matter, are aware that you’ll need to get out and lock the hubs on that Troopy before pulling back on the transfer-case lever.

Just a partial table of contents

Just a partial table of contents

The driving section then begins with another vital subject: mechanical sympathy; that is, how to drive with awareness of the vehicle and the right touch to avoid stressing or breaking it. Further discussions cover suspension articulation, low range and when to use or not use it, throttle and brake control, followed by extensive sections on types of terrain and the techniques used in each: sand, mud, tracks, deep ruts, rocks, water. What is the correct way to ascend or descend or traverse a steep slope? To cross a deep ditch or sharp ridge? Negotiate snow or ice? It’s all in here.


The following extensive section is all about recovery, both assisted and solo, and includes an utterly brilliant chapter on winching. :-) A short but fascinating chapter on advanced driving covers such arcane skills as changing from low to high range on the move, or driving a non-synchro transmission—just in case you ever get the chance to take a Bedford RL on safari. There are also useful sections on trailer towing for those of you with adventure-type trailers.

That would be a complete book, but Tom continues with a section on expedition basics—sort of a flash introduction to the last word on the subject, his Vehicle-dependent Expedition Guide—as well as sections on loading and lashing, equipment, fuels, oils, tyre repair, and vehicle selection for expeditions.

That front section, however, is why you should buy this book. For the fifth edition Tom immersed himself in the latest models and technology and updated anything that remotely hinted at being past its sell-by date. There’s even a brief flash of a disguised Rolls-Royce Cullinan careening along the face of a sand dune, with a typical Sheppard wise-cracking caption: “No, your Ladyship, the brake is on the LEFT! And Rolls is the marque, not the aim.”

Read this book. Then go get some professional instruction. I’ll bet you at some point your instructor will look over at you and say, “You’ve done this before, haven’t you?”

Factory vs. aftermarket

Aftermarket starter on the left; Toyota starter on the right

Aftermarket starter on the left; Toyota starter on the right

If you’ve ever turned over an engine by hand you know it’s no easy thing to do. You’re working against a lot of internal friction, plus the compression as each piston rises on the firing stroke. Your starter has to do the same job, except a lot faster. So it clearly needs to be built well.

Take a look at these two starters for a Land Cruiser F or 2F engine—an aftermarket unit on the left and a factory Toyota unit on the right. If you’re not familiar with how a starter works, notice the small gear visible at the top of each unit. When you turn the ignition key to start the engine, that gear slides forward and engages the flywheel behind the engine, and spins it rapidly to enable the ignition to catch and start the engine. Once it starts and you release the key, the gear slides back out of engagement.

It should be obvious that that gear is subjected to a great deal of stress—which is why the factory starter has a nose cone that supports the end of the shaft on which the gear slides, hugely increasing its stiffness (and also possibly helping keep random dirt and debris away from the shaft and gear).

Now look at the aftermarket starter. No nose cone, no support for the gear. Cheaper to make, for sure.

Which would you expect to last longer?

The truth about aftermarket "high-performance" brakes.


Few people reading this would argue that the single most important component of your vehicle is the braking system. Everything else—engine power, handling, comfort, fuel economy, off-pavement capability, number of USB outlets—is secondary to the critical need to be able to stop that vehicle safely and quickly, time after time.

Yet despite that single-purpose, critical function, there are a lot of myths circulating about brakes, how they work, and how they can be improved—and a lot of those myths originate from, or are promulgated by, companies trying to sell you something.

In terms of physics, brakes do exactly one thing: They convert the kinetic energy of the moving vehicle into thermal energy, i.e. heat. All brakes function this way, whether disc, drum, or Fred Flintstone’s feet. In fact, even the parachute on a top-fuel dragster converts the kinetic energy of the vehicle into heat, through friction with the atmosphere; it is simply dissipated more diffusely in the dragster’s slipstream.

The energy those brakes must convert does not increase linearly with speed; instead it increases with the square of speed (kinetic energy equals mass times velocity squared). Thus a vehicle moving at 50 mph requires four times as much energy conversion to stop as one moving at 25 mph, and one moving at 100 mph requires sixteen times as much. Given the same speed and the same vehicle weight, the heat produced by stopping is also the same, whether it is done via cast-iron drum brakes on a Series 2 Land Rover or the carbon-ceramic discs on a Porsche GT3.

The basic operation of a brake goes like this: When the driver presses the brake pedal, the pedal pushes a plunger into a hydraulic cylinder filled with brake fluid—a viscous substance resistant to heat. The cylinder, called the master cylinder, is connected to a brake caliper in each wheel via tubes. The caliper wraps around the perimeter of the brake disc, and incorporates a piston on each side (sometimes several), which bear against brake pads made of friction-resistant material. The master cylinder forces the brake fluid, which is essentially incompressible (more about that later) through the tube and against the pistons in the caliper, which in turn push the brake pads against the disc, squeezing the disc (also called the rotor) with tremendous force, creating friction and slowing the vehicle.


The drum brake, which has virtually disappeared except on the rear axles of the cheapest economy cars and Toyota Tacomas (see here), is different. Instead of a flat disc there is a cast-iron drum shaped like a flat pan with vertical sides, turned vertically so it rotates with the wheel. The master cylinder pushes against a slave cylinder (a quaint term, no?) which in turn pushes a friction-resistant brake “shoe” against the drum. Drum brakes have (mostly) gone the way of flathead V8s and carburetors because they retain more heat (more on that soon) and don’t work well when wet.

There have been many advances to the basic hydraulic braking system. Originally (and still in a few applications) each caliper employed only one piston and the caliper could slide slightly back and forth. The piston pushed one brake pad against the disk while simultaneously pulling the opposite pad against the other side. This was much less efficient than the later multi-piston calipers. Modern brake calipers on high-performance sports cars can employ six or even eight opposed pistons.

Virtually all brakes today are power-assisted via a vacuum-operated device incorporated into the master cylinder. This reduces braking effort, sometimes hugely in the case of a heavy truck. Also, all brake systems are now (by law) dual-circuit: The master cylinder is essentially two master cylinders combined in line, each of which operates on both front brakes and one rear brake. This redundancy insures that if one circuit fails, the vehicle will still retain reasonable stopping power.

A big advance in the efficiency of brakes arrived with anti-lock braking systems (ABS), which use a simple sensor at each wheel to monitor revolutions of the wheel. If a sensor detects a wheel locking up (i.e. turning slower than the others or stopping altogether), the ABS computer pulses power to that brake so that it unlocks. This system reduces braking distances and increases the driver’s control over the vehicle. (To see why a turning tire stops shorter than a skidding tire, look here.)

As vehicles have become heavier—and wheel diameters larger—manufacturers have been installing larger and larger-diameter discs in their brake systems. Most disc brakes are now ventilated—the disc comprises two discs joined by a vaned center section to dissipate heat more effectively. Thanks to such advances—as well as better tire compounds—average braking distances have been steadily shrinking.


Obviously it’s easier to stop a light vehicle than a heavy one. By extension we can state categorically that it is easier to stop, say, a stock FJ60 Land Cruiser than one that has been modified with an ARB winch bumper and a Warn 9,000-pound winch, a rear spare/jerry can rack, a roof rack, a 60-liter fridge, a drawer system, an auxiliary fuel tank, and . . . you get the picture. With surprising suddenness your 5,000-pound Land Cruiser x velocity squared can become a 7,000-pound Land Cruiser x velocity squared.

I discovered the results on our own FJ60 on a biological survey in Mexico’s Sierra Madre some years back. This 60 had a turbodiesel engine conversion plus most everything on the list above. And on a steep, winding descent of about 3,000 feet, the brake pedal began to feel mushier and mushier, even as I downshifted to use engine braking. By the time we reached the plains the brakes had seriously deteriorated, and only regained effectiveness after ten minutes of cooling down.

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I had experienced classic brake fade.

Brake fade can occur essentially two ways. First, a brake pad can overheat from extended application—such as a long descent—and form a slick glaze on its surface. When this happens the brake pedal will still feel firm, but increased pressure will have little or no effect. Second, the brake fluid itself can heat to its boiling point. When this happens, the fluid turns to a gas—and gas, unlike the fluid, is compressible. So your desperate standing on the pedal just compresses the gas in the calipers and does little to squeeze the brake pads. This is what we experienced. The condition can be aggravated if you don’t regularly flush your brake system. Brake fluid is hygroscopic, meaning it absorbs water, and since water has a much lower boiling point than pure brake fluid, old, contaminated fluid can cause premature boiling and fade.

Of course even stock vehicles with no weighty accessories bolted to them can be subject to brake fade, and even if no calamities ensue when it occurs it is a deeply unsettling experience. The logical first response is, “I need better brakes!” Indubitably true, but the path to obtaining them is fraught with hype and numerous ways to spend lots of money for very little if any gain.

Let’s start with that brake fluid. Brake fluid is graded on a DOT scale, based on its minimum  boiling point, both dry (uncontaminated with water), and wet (contaminated). Most braking systems come from the factory filled with DOT 3 fluid, which has a minimum boiling point of  401ºF dry and 284º wet (see now how much water can degrade your brakes?). Dot 4 fluid is rated at 446º and 311º minimum, respectively, and DOT 5.1 fluid carries a 518º and 374º rating. So simply spending 20 bucks or so upgrading your brake fluid can give you a full 100-degree margin over DOT 3 before gassing occurs. Note that these standards are minimums; many premium brake fluids will perform well above that and will say so on the label. And what happened to DOT 5 fluid? That’s a silicone-based fluid as opposed to the glycol base of DOT 3, 4, and 5.1. You can mix glycol-based fluids all you like, but cannot mix glycol and silicone fluids.

It will do little good to install better, high-temp brake fluid if your brake pads are sub-standard. Most vehicles come from the factory with organic-compound pads, or NAO (non-asbestos organic). These are sufficient for most use—they are quiet, don’t create much brake dust, and are easy on the discs—but if overheated can be subject to the glazing we discussed earlier. Semi-metallic pads, which are a mixture of iron, copper, steel, and graphite in an organic matrix, are significantly more resistant to glazing, at the expense of (sometimes) more noise, more dust, and faster disc wear—and of course slightly higher cost. A third type of brake pad, ceramic, attempts to solve the noise and dust issues of semi-metallic pads, and is resistant to fade, but less aggressive and generally not recommended for heavy-duty use, especially in cold climates—although the technology is still advancing..

So if your braking system is in good order, you’ve upgraded your brake fluid and switched to semi-metallic pads, and you’re still experiencing brake fade, what then? (I’ll refrain from suggesting, “Leave some of that crap at home.”) It might be time for a more drastic upgrade.

And that’s where marketing hype gets really tricky.

Many commercial kits (as well as a whole bunch of do-it-yourself threads on forums) “upgrade” the front brakes—where most braking occurs—simply by means of replacement calipers with more and/or larger pistons and larger pads than the originals. More pistons equals more squeeze and better braking, right?

Not so fast.

Remember all that kinetic energy we’re turning into thermal energy every time we stop? That energy (heat) has to be dissipated to enable repeated stops—or a safe descent down a mountain grade—without overheating the pads or brake fluid. And the way that heat is dissipated is through the brake disc. So if you install more powerful calipers on your existing discs, here’s what’s likely to happen: You’ll take the vehicle out for a trial run around town, and be impressed at the increase in stopping power. Those new four- or six-piston calipers grab that disc right now. Awesome. So you’ll then head confidently to that long downhill that resulted in a scary spongy brake pedal last month, and . . . oh. Whoa. Halfway down, the pedal feels like it’s got an entire bag of Sta-Puft marshmallows between it and the calipers. That’s because you’ve installed the means to inject more heat into the braking system without installing the means to get rid of it. As long as you’re just trundling around town you’ll get some benefit from the more powerful calipers, but under prolonged application all they’re likely to do is make your fade problem worse.


Okay . . . plan B then. Let’s install a set of those fancy (and awesome-looking) cross-drilled brake discs. You know, like Porsches and Ferraris have? Cross-drilled discs stay cooler, right, with all those holes?


Sorry . . . wrong again.

Cross-drilling of brake discs began in the early days of disc brakes, when existing pad materials and adhesives tended to outgas strongly when heated. Cross-drilling relieved the fractional layer of (compressible, remember) gas the pad would exude between it and the disc. But modern brake pads exhibit virtually none of this outgassing. More importantly, a cast-iron brake disc relies on its mass to absorb and dissipate heat. When you drill a bunch of holes in it, you are reducing that mass. (One company actually boasts that its drilled discs are 16 percent lighter than non-drilled discs.) Some arguments—especially from those who sell them—still maintain that the ventilation and added surface area of cross-drilled discs provide enough cooling to offset the loss of mass. But the further I investigated, the more testimonials I read from objective experts in the field who called nonsense. At best, many referred to any cooling effect as a wash, and several pointed out how often cross-drilled discs wind up plugged with brake dust—a giveaway that not much air flow is occurring through those holes (unlike the well-documented radial flow through the center vanes of a ventilated disc). Add to that the fact that, even when properly cast in and chamfered rather than simply drilled, cross-drilling can introduce stress risers into the disc that promote cracking, and you have a powerful argument against it, no matter how stylish it looks. (And if you look at the ads from companies who sell them you’ll be amused at how many mention the style factor as an actual reason to spend your money.)

The sole theoretical advantage to drilled discs mentioned by those same experts was a slightly enhanced initial “bite” in wet conditions, when the holes might provide an exit for surficial water on the disc. But brake pads quickly squeegee water off that surface anyway, so even this attribute is of questionable value in the face of the expense and loss in mass of a drilled disc.

Thus we can say pretty confidently that replacing your plain brake discs with cross-drilled discs of the same size will probably result in no reduction in fade, and could conceivably exacerbate it.

(Incidentally, the above does not apply to disc brakes on motorcycles, since a motorcycle disc is a solid rotor rather than a vented, double-sided unit. On a solid rotor, cross-drilling does create some turbulent cooling flow.)

What about the more recently popular slotted discs? Slots actually perform a different function than drilling. The edges of the slots perform a microscopic scraping function on the pad, keeping the pad surface fresh and possibly forestalling glazing. While they won’t in themselves enhance cooling or prevent heat-related fade, they might help forestall the fade resulting from overheated pads of inferior composition. Be advised, however, that slotted discs, as you might expect, will wear out pads more quickly than solid discs, and are likely to exacerbate any brake-dust issues.

Inevitably, aftermarket manufacturers are now offering discs that are both cross-drilled and slotted. At least the slots will provide some function, and where the slots are there is less room for the pointless holes . . . 


All this leads to a logical conclusion. Once you’re optimized your brake fluid and brake pads—and assuming the rest of your braking system is operating as it should—the only sure way to add braking power and reduce the chance of fade is to install, surprise, larger brakes—specifically discs of larger diameter and/or width, with calipers to match. Sometimes this is possible within the constraints of your existing wheels and front end design, sometimes it is not. 

Automobile manufacturers are perfectly aware of this. To give you a random example—outside the realm of overland vehicles but one with which I’m familiar—when Porsche upgraded the 1983 911SC to the 1984 Carrera, including a 15-percent bump in power, they improved the braking by increasing the width of the front brake discs from 20 to 24 millimeters, while keeping the diameter the same at 289mm. For the significantly more powerful Turbo of the same era, they increased both the diameter and the width of the discs, to 300 and 32mm respectively. Those were the largest brakes that could fit within the factory 16-inch-diameter wheels. When Porsche added even more power, they switched to larger-diameter wheels as well to accommodate larger discs.

There is one minor exception to the only-bigger-is-better rule. If you look at different aftermarket discs, you’ll notice significant variations in the spacing of the center cooling vanes. Inexpensive discs will be made with more widely spaced slots, which means there is both less mass in the disc to radiate thermal energy, and less radial air flow as well. The one way an aftermarket disc of the same dimensions as the stock disc might outperform it is if the aftermarket disc has a higher density of vanes, and thus weighs more than the stock disc. StopTech, for example, makes a replacement disc for the Tacoma that is stock diameter, but weighs over a pound more, thanks to more closely spaced vanes. That translates to more thermal capacity.

A comparison of vane spacing on a vented brake disc.

A comparison of vane spacing on a vented brake disc.

Looking at our own class of vehicles, it is all too easy to find “high-performance” brake kits comprising nothing but inexpensive stock-sized replacement discs that have been cross-drilled and/or slotted. Some of the claims for these border on outrageous.

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Note that line, “Improves stopping power up to 30 percent over stock brake rotors.” Seriously? Thirty percent meaning 30-percent shorter stopping distances? Or thirty percent less fade? I’d love to see an independent test of that claim. Also, there is simply no chance that their “custom slots” do any cooling, and they will more than likely increase dust due to the scraping function. Finally, check the “reducing heat” claim at the top, which we know from physics is impossible. The only component in this kit likely to modestly improve braking performance is the semi-metallic pads, if they are replacing stock pads—and those certainly won’t “reduce noise.” That’s a stunning amount of misinformation in a single ad.

Finding kits to actually upgrade brakes is much, much harder, in part because it so often requires installing larger-diameter wheels as well. TRD offers a front disc upgrade kit for Tacomas that increases the disc size from 319mm to 332 mm but still fits within the stock wheels. That’s a worthwhile enhancement.

Redline Land Cruisers offers a Big Brake kit for the front of FJ40s, 55s, and 60s that increases the disc diameter from 12 inches to a full 13.3 inches and includes calipers from a later 100-series Land Cruiser—a significant upgrade. But the kit requires a switch to 17-inch wheels for clearance (the company also wisely recommends rear discs, a larger master cylinder, and a proportioning valve to correctly balance front-to-rear braking force). They also mention a big brake kit for 16-inch wheels, but I’ve not received any more information on that one.

I’ve seen a few other legitimate kits for various vehicles, but there is far more in the way of chaff to wade through to find it. The good news is, I suspect for the majority of us a simple upgrade to better pads and fluid will solve anything but chronic brake fade. If that won’t do it, at least now I hope you’ll be better able to distinguish hype from fact. 

And if you really want to drill holes in something, maybe you could take up carpentry . . .

JL Wrangler frame issues

Photo: Brett Stevens

Photo: Brett Stevens

The folks over at Jalopnik have a good and extremely important article about the issues some owners are having with welds on JL Wranglers. The critical issue is the weld that holds the track bar to the frame, and the article includes photos and a video of the problem.

The track bar is what locates the front axle side to side, so if it goes so does directional control and steering—not a good thing.

If you own a JL Wrangler you will probably be receiving information about this, but in the meantime you might want to take action yourself. Reportedly FCA has issued a stop-sale order until the matter is addressed.

Open diffs, lockers, and traction control

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Many years ago I was exploring a trail in the mountains east of Tucson, Arizona, in my FJ40, and came upon a couple in a shiny new 4x4 Toyota pickup. They had managed to high-center the transmission skid plate on a rock ledge, so that the right front and left rear tires of the truck hung just an inch or two in the air and spun uselessly when the fellow applied throttle. The couple, new to backcountry driving, was bewildered that their “four-wheel-drive” vehicle had been rendered completely immobile by such a minor obstacle, and were convinced something was wrong with the truck. I picked up a fist-sized rock from the side of the trail and kicked it solidly under the hanging rear tire. “Try it now,” I said—and the Toyota bumped free. They were astonished and even more bewildered—until I explained how a differential works.

When any four-wheeled vehicle makes a turn, each wheel needs to rotate at a different speed because it travels a different line than the others, and thus a different distance. If, for example, the two rear wheels were locked together with a solid axle, the tires would scrub horribly every time the vehicle turned, and handling would be affected dangerously. Thus we divide that axle in two and connect them with a differential—a system of gears that transfers power from the driveshaft to the wheels while allowing them to rotate at different speeds in a turn. In a four-wheel-drive vehicle we add another driveshaft and differential at the front, so those wheels can be driven as well.

But an open differential, as this is known, has a major inherent flaw, especially for those of us who own 4x4s: If one tire loses traction, the differential gears, in effect, route all power to that side of the axle. Thus if you stop with one wheel on a solid surface and the other in mud—or hanging in the air—the tire with grip will remain stubbornly motionless while the other just spins. (Technically both wheels are receiving the same amount of torque, but the amount required to spin the low-traction tire is not enough to move the vehicle with the other tire.) So my friends in the Toyota pickup found themselves in a situation in which the power being delivered to the front axle was expended on the tire that was off the ground, while the same thing happened in the rear. Once I stuffed that insignificant rock under the hanging rear tire, the full torque of the engine was available and the truck pulled itself free.

Ironically, the drawbacks of open differentials became more apparent with the advent of so-called full-time four-wheel-drive vehicles such as Land Rover’s Defender. In a part-time 4x4, the front and rear driveshafts are locked together at the transfer case when four wheel drive is engaged, so power is always equally distributed to both axles and therefore to at least one wheel in front and one in back—but you cannot drive on pavement with four-wheel drive engaged or the tires will scrub and the gears will bind. The Defender (along with other vehicles such as the Mercedes Benz G-Wagen) allows engine power to be directed to both ends of the vehicle, regardless of the surface, by employing a third differential in the transfer case to allow the front and rear driveshafts to turn at different speeds on pavement and prevent binding. To ensure equal power to both ends of the vehicle on trails, the center differential can be locked manually. But if that lock fails—as happened to me in a Defender 110 on a remote route up the west wall of Kenya’s Great Rift Valley—you are left with a one-wheel-drive vehicle. When my front axle unloaded on the steep grade, all power went to that axle through the open transfer-case diff, and as soon as one front wheel unloaded I was completely immobilized with a single tire spinning fruitlessly—on a scary 40-percent grade with a steep dropoff. (I was towed the rest of the way up the escarpment when, improbably, a battered Land Cruiser appeared driven by none other than Philip Leakey . . .)

Over the decades, various attempts have been made to allow the differential to function properly in turns while maintaining full traction when needed. Way back in 1932 the engineering firm ZF, at the request of Ferdinand Porsche, invented a “limited-slip” differential to prevent the high-powered Auto Union Grand Prix cars Porsche had designed from spinning their inside tires when exiting turns. In the succeeding decades, many American manufacturers installed limited-slip differentials in their trucks to help enhance traction on slippery surfaces, and several types were developed. Some used clutch packs to transfer power, others (Torsen, Quaife) used gears, and some—especially those designed to be installed in transfer cases—used hydraulic fluid. 

But limited-slip diffs are just what their name implies—they cannot completely prevent loss of traction in challenging conditions. The best way to ensure full traction when it’s needed is to lock both halves of the axle together, thus ensuring ideal power delivery even if one wheel is off the ground. But once you do that you’re right back to our initial problem with tire scrub and gear windup. The trick, then is to have the differential lock only in conditions where it would be beneficial—or to have it locked all the time except when turning. This can be accomplished either automatically or manually.

In 1941 a fellow named Ray Thornton patented an automatic locking differential he called the  Thornton NoSPIN Differential. It was manufactured by the Detroit Automotive Product Corporation and installed in many WWII military vehicles. The NoSPIN employed a series of clutch packs and a spring-loaded cam gear, which kept the axles locked together unless the vehicle was turning a corner, when the cam disengaged the clutch packs from the spider gears and allowed the wheels to rotate at different speeds. In the 1960s American truck manufacturers began installing the NoSPIN in light-duty trucks as an option—and it gained its nickname, the Detroit Locker. While extremely effective, the Detroit Locker suffered from noisy operation on pavement as the gears engaged and disengaged, and handling that could sometimes be jerky as power transferred between one and two wheels. (Later models have attenuated these characteristics somewhat, but the transition is still noticeable to the driver.) A similar product made by the Eaton Corporation was introduced on 1973 General Motors light trucks, and Eaton subsequently bought the parent company of the Detroit Locker. 

The mechanism of the Detroit Locker and its relatives replaces a large part of the differential, requires precision resetting of pinion backlash, and is thus expensive and time-consuming to install as an aftermarket option. Not so with so-called “lunchbox” lockers such as the clever Lock-Right, which replace only the spider gears and can be installed in an afternoon by a competent home mechanic. The Lock-Right and its kin keep both axles locked together until the vehicle turns, at which point the internal drive plates ratchet past each other and allow the outside wheel to turn faster than the inside wheel. On the trail, full power is available to both wheels, even if one is airborne.

The Aussie Locker is typical of so-called "lunchbox lockers."

The Aussie Locker is typical of so-called "lunchbox lockers."

Opinions differ on the “lunchbox” nickname—some claim it’s because the unit will fit in a lunchbox, others because you can install one in the time it takes to eat a sandwich and chips (somewhat optimistic). Regardless, this type of locker is the most affordable and easy way to gain true diff-locking capability for your 4x4. However (there’s always a however), the Lock-Right-type lockers are restricted in strength depending on what the carrier is designed for, and are generally not recommended for tires over 33 inches in diameter. They can also be noisy on the street, as the ratcheting becomes noticeable around corners. And I would strongly dis-recommend them for installation in the front axle, as steering will be significantly affected (and, as with the Detroit Locker, they should never be installed in a front axle that does not have free-wheeling hubs).

Automatic lockers have their fans, but arguably the best locking differential is one the driver can control. The Australian company ARB popularized the air-activated locking differential after buying the rights to the Roberts Diff-Lock in 1987—and it transformed the capability of the Land Cruisers and Land Rovers in which it was first deployed. For most driving, a differential with an ARB unit installed acts as a normal open differential—no noise, no steering effects or increased tire wear. But when traction is lost—or, significantly, when the driver observes a spot ahead of the vehicle where traction might be lost—the locker can be engaged and the obstacle traversed smoothly and easily. Once back on a solid substrate the diff can be unlocked and returned to normal function. A small compressor (which can double for filling tires) activates the locker by pushing a sliding pin in the differential. The ARB locker is now available for a huge range of vehicles, and while its installation is as complex as that of the Detroit Locker (with the wince-inducing addition of needing to drill and tap a hole in the differential housing for the air line), its reliability and astounding capability has been proven over millions of miles.

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It took a few years, but vehicle manufacturers caught on to the benefits and capabilities of selectable diff locks. Toyota introduced an electrically operated rear differential lock in its TRD package for the Tacoma, and optional front and rear diff locks in the 70 and 80-series Land Cruisers. The Mercedes G-Wagen has front and rear locks, as does the Rubicon version of Jeep’s Wrangler, and the Ram Power Wagon, among other vehicles. Until you’ve climbed a 45-degree slope in a vehicle with both diffs locked—and, thus, true four-wheel drive—it’s difficult to imagine the gravity-defying traction available. Even experienced passengers gasp and scrabble for handholds as high-noon sun floods through the windshield. (Showoffs are advised to keep in mind that with the front diff locked steering is very difficult; it should only be employed when absolutely necessary and for as short a distance as possible.)

To explore the next step in making four-wheel-drive vehicles truly four wheel drive we need to do a 180-degree turn and look at . . . brakes: specifically anti-lock braking systems. 

While ABS has been around in one form or another since 1929, when a primitive mechanical system was developed for aircraft, it was Mercedes Benz that introduced the first fully electronic, multi-channel four-wheel anti-lock braking system as an option in 1978. ABS relies on a deceptively simple system of sensors at each wheel, individual hydraulic pumps for the calipers, and a computer control. The sensors do nothing more than count the number of rotations per unit of time for each wheel. When one or more of the sensors detects a wheel turning slower than the others during braking—as when a tires locks and stops rotating altogether, increasing braking distance and hampering steering control—the computer reduces braking force to that wheel, pulsing the pressure many times a second to maintain static friction between tire and surface. Soon this system was exploited to provide electronic stability control (ESC), to help road cars maintain traction in slippery conditions.

And then—lucky for us—a light went on in an engineer’s head that this system could also be used to enhance traction in four-wheel-drive vehicles. It’s accomplished by exploiting the characteristics of the open differential.

Recall the offside wheels on that poor Toyota pickup spinning helplessly in the air. With an electronic traction-control (ETC) system, those versatile ABS sensors send that information to the computer, which applies braking force to the spinning tire or tires. The open differential is “tricked” into increasing torque to the tires on the ground, and the vehicle pulls itself free. Land Rover debuted ETC on its 1993 Range Rover, and off-road driving has never been the same. Advances in programming and technology have since brought us to the point that some vehicles can maintain forward progress with traction to only one wheel.

That would be miraculous on its own, but engineers weren’t finished yet. One of the most challenging conditions facing a driver on trails is a steep descent. In an older vehicle such as my FJ40, if you stomped on the brakes in a panic on a steep downhill section, the unloaded rear brakes would lock and the vehicle would instantly try to swap ends. Descending such slopes meant using first-gear-low-range engine braking and careful cadence foot-braking to make it down safely. In a vehicle with automatic transmission (and thus little engine braking) the situation was even dicier. Enter hill-descent control: Punch a button, point the vehicle downhill, and steer. The ABS and computer can selectively brake individual tires if necessary to maintain a steady walking pace and prevent lockup on truly hair-raising slopes. No driver, no matter how skilled, can equal that.

I remember my initial experience in a vehicle equipped with ETC and hill-descent control. At first the chattering, juddering progress up and down steep ridges was alarming—it sounded like something was seriously wrong. But I soon got used to it and realized how effortlessly I was conquering obstacles that had required all my attention in the FJ40. 

Is electronic traction control, then, superior to manually lockable differentials? The definitive answer is: It depends. Remember that a skilled driver using manual diff locks can anticipate the need for extra traction and respond in advance, thus frequently avoiding drama of any kind. By comparison, a traction-control system must detect a difference in wheel speed before it reacts, and the computer must decide if action is required or if the driver is simply turning. In some vehicles I’ve driven a considerable amount of throttle—and trail-damaging wheelspin—is necessary before the system kicks in. Increasingly, however, manufacturers are incorporating driver-selectable, terrain-specific algorithms that quicken response when the vehicle is in low range, for example. These algorithms can also modify throttle response and shifting to suit conditions. Land Rover was a pioneer in this technology with their Terrain Response dial. Some vehicles, such as Jeep’s Wrangler Rubicon, incorporate both ETC and manual diff locks—the very best of both worlds.

The Nissan Titan XD's traction control will pull it through situations such as this, but not without some wheel spin.

The Nissan Titan XD's traction control will pull it through situations such as this, but not without some wheel spin.

One could argue that these computer-controlled tricks reduce the skill formerly required of the driver. Indubitably true to an extent—surely I feel I paid my dues with my leaf-sprung, open-diffed 1973 Land Cruiser over the years. Yet in the sybaritic, climate-controlled cockpit of a Land Rover LR4 or Jeep Wrangler Rubicon I can traverse terrain that would have the FJ40 struggling. If technology makes it easier for new enthusiasts to get out and explore the backcountry, I’m all for it—even if I don’t get to show off as often getting them unstuck with a fist-sized rock. 

The Holy Grail of FJ40 wheels and tires?

I’ve owned my FJ40 long enough to have gone through several generations of tire and wheel combinations. When I bought it it still had the factory steel 15 x 5.5-inch rims (with hubcaps), and absurdly skinny and short 215-series tires of a brand I do not recall, but which were genuinely tiny enough to hamper its performance on trails.

Santa Catalina Mountains, 1978

Santa Catalina Mountains, 1978

As soon as I could afford it I bought a set of then-de rigueur 15 x 8 white spoke steel wheels, and mounted larger Armstrong Norseman tires. Big improvement, although I could feel the increase in steering effort through the non-boosted box. At the same time I gave away those factory wheels and hubcaps—dumb move.

And there it stayed until the late 1980s, when I was starting to be aware of how things were done in other parts of the world. I became convinced that split-rim wheels were the absolute ultimate way to go—after all, you could break down a wheel and repair a tire anywhere, right? They were still standard equipment on Land Cruisers in Africa and Australia, right? So at some considerable expense I ordered a set of Toyota factory 16 x 5.5 split rims. When they arrived I was somewhat put off by their mass—they made the eight-inch steel white spokers seem light—but duly had mounted a set of LT 235/85 16 BFG All-Terrains. 

In short order two tire-shredding blowouts revealed that something was not right. It developed that the tire retailer had installed improper liners in the wheels. That was corrected, and despite shaken confidence I began employing the Land Cruiser as a support vehicle while leading sea kayaking trips from remote beaches in Mexico. And indeed it was true: I could break down a wheel and repair a puncture anywhere. Clients were impressed. Several times.

With a split-rim wheel and tubed tire, any puncture means completely breaking down the wheel to patch the tube. A nail hole that could be fixed in five minutes with a plug kit required 45 minutes of hard labor. The romance was wearing thin. By this time I was chalking up some experience in Africa with split-rim-equipped vehicles, and noticed a difference there. First—purely personal theorizing here—the economy of most African countries meant that random nails and screws lying on roads simply didn’t exist. They were too valuable. Also, the tires employed there are typically eight or ten-ply bias-belted 7.50 x 16 beasts that seem more or less immune to simple thorn punctures. I was experiencing fewer punctures on the back roads of developing-world countries—both in vehicles I drove and those in which I was driven while on assignment—than I was in the U.S. and Mexico.

African Firestone tire on a split rim.

African Firestone tire on a split rim.

By now I had replaced the three-speed transmission in the FJ40 with an H41, a four-speed with a low, 4.9:1 first gear. I thought that would allow me to install a slightly taller tire—and I was ready to dump the split rims and try alloy wheels. So on went a set of American Racing Outlaw II 16 x 7-inch wheels, and LT255/85 16 BFG Mud-Terrain tires. Given the two-inch OME lift on the vehicle, this was the outer limit of what would fit without clearance issues or ghastly body-cutting and cheesy riveted-on fender flares. Indeed at full left lock the left tire slightly contacted the steering box link. But otherwise the tires worked fine, and the combination stayed on for over a decade.

Still . . .

Two things began to nibble at my subconscious. First was the memory of those BFG All-Terrains in 235/85 16. So many things about the size seemed perfect. They were tall enough to noticeably benefit ground clearance, yet their narrow tread width made steering easy. Also, by this time the Land Cruiser had become something of a classic rather than just an old four-wheel-drive “jeep,” and I was kind of missing the whimsical look of those factory hubcaps. It would be easy to buy a replacement set of Toyota 15 x 5.5-inch wheels and hubcaps—but there was no tire size in BFG’s 15-inch lineup equivalent to the 235/85 16. For a while BFG sold a 9.5 x 33-inch All-Terrain that would have worked, but it was discontinued. Some owners (and, by now, professional restorers), were squeezing 31 x 10.5 All-Terrains on factory wheels, but those were not quite tall enough and not quite narrow enough to suit. (The size is also technically far too wide for a 5.5-inch wheel.)

What I needed was a 16 x 5.5-inch wheel with clips for the factory hubcaps—and out of the blue a few months ago my friend Tim Hüber sent me a link to exactly that, available from Japan. They were . . . expensive, eye-wateringly so. And would additionally need to be powder-coated a proper gray, adding even more expense. But it was exactly the Holy Grail for which I had been searching.

Ordered, delivered, powder-coated, mounted. And . . . indeed, perfect. The ideal all-around tire size for an FJ40, and the amusingly perfect retro pukka look, too. 

One genuine surprise: I assumed going to a steel wheel from an alloy—even with a smaller tire—would add significant unsprung weight. Not so. One alloy wheel and 255/85 16 Mud-Terrain tipped my hanging scale at 73.2 pounds. The steel wheel and 235/85 16 All-Terrain? Seventy four pounds even.

Never say never, but I predict this will be the final solution to the Land Cruiser’s footwear.

Left: 16 x 7 Alloy and 255/85 16 MT. Right: 16 x 5.5 steel and 235/85 16 AT. Same weight.

Left: 16 x 7 Alloy and 255/85 16 MT. Right: 16 x 5.5 steel and 235/85 16 AT. Same weight.

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Now that's a proper suspension analysis

Our last trip to Australia and Tasmania, the first with all the modifications and additions to our Troopy completed, revealed some shortcomings in the suspension—no surprise with 180 liters of fuel and 90 liters of water on board, in addition to the cabinetry, pop-top, bumper and winch, etc. etc. It wasn't bad—the rear sagged perhaps an inch with everything aboard including us—but an inch is too much, and we could feel the shocks working hard to maintain control.

Daniel at the Expedition Centre in Sydney, who'd done all the work on the vehicle, had just one recommendation: A company called, humbly enough, The Ultimate Suspension.

TUS, as I'll call them, advertises "custom-built, fully integrated" suspension systems designed specifically for each vehicle, not just each model. After receiving the analysis above, I can't argue that their approach isn't thorough. I'm not sure what the percentages in the shock absorbers refer to—would 100 percent mean it's as comfortable as a Range Rover? Must ask. In any case it's interesting to see the weight at each corner and across the vehicle, and to know that (ahem, rather surprisingly) we're still safely under the Land Cruiser's GVWR, even with a full load of fuel and water.

An ARB diff lock for the FJ40

I waited 38 years to install an ARB differential locker in my FJ40.

Why so long, and what made me finally decide to do it? A number of reasons explain the delay. First is that the ARB diff lock did not exist until 1987—a pretty ironclad excuse for the first ten years I owned the vehicle. By the time I became aware of the product and its potential, in the early 1990s, I was using the Land Cruiser as a support vehicle for guiding sea kayak trips in Mexico. And sea kayak guides do not make enough to buy ARB lockers. Several years later I moved on to freelance writing—and freelance writers do not etc. etc.

By this time another factor was at work. Through much, much trial and error I had become intimately familiar with the vehicle and its capabilities on difficult trails, to the point that I could predict accurately when a wheel was going to lift, when a cross-axle obstacle would unload diagonal tires enough to steal traction, just how much momentum I needed to get through spots that would have been effortless with a locker. Thus I was beginning to enjoy successfully traversing trails in Arizona that were considered fairly advanced even with traction aids, and a sort of reverse snobbery seduced me. Of course there were plenty of challenges simply beyond the ability of an FJ40 with open diffs, a two-inch lift, and 31-inch-tall tires, but I was happy with the places I’d been.

The fun part: drilling a hole in a perfectly good differential housing.

The fun part: drilling a hole in a perfectly good differential housing.

That attitude began to change when I had a Jeep Wrangler Rubicon Unlimited for a year as a long-term review vehicle for Overland Journal. The Rubicon, with its compliant all-coil suspension, driver-disconnectable front anti-roll bar—and selectable diff locks front and rear—could traverse terrain elegantly that the FJ40 traversed awkwardly. At the time I was stressing—and, a few years later, at the Overland Expo, teaching—environmentally conscientious driving, techniques far beyond the facile “Stay on the trail” message of Tread Lightly. One overriding goal of this is to avoid wheelspin if at all possible—an approach that is easier on the vehicle, the tires, and the trail. In the FJ40 some wheelspin was almost inevitable to get through sections that unloaded two tires, even with judicious left-foot braking, which can reduce but not eliminate it. In the Wrangler I could scan the terrain in front, predict which spots might unload the tires, and engage one or both lockers ahead of time, resulting in perfectly smooth progress. (This, by the way, is the salient advantage of driver-selectable lockers over ABS-based traction-control systems, even the best of which which must detect some wheelspin before they activate.)

Also contributing to my change of mind was the increasing capabilities of almost all current four-wheel-drive vehicles—some, such as that Wrangler and our Tacoma, equipped with factory locking diffs, many others with increasingly sophisticated traction control, even "lesser" models firmly in the cute ute category. Despite its relative primitiveness, I’ve kept the FJ40 competitive in some ways—on Old Man Emu suspension it rides better than our Tacoma did stock and has excellent compliance; it has a best-in-class Warn 8274 winch, good driving lights, a superb no-longer-made Stout Equipment rear bumper and tire/can carrier, a fridge, even a stainless-steel 14-gallon water tank. But newer vehicles were simply outclassing it in traction. 

Fast-forward to earlier this year, when I shipped the Land Cruiser to Bill’s Toy Shop in Farmington, New Mexico, for a complete engine and transmission/transfer case rebuild. As long as it was up there . . . 

I decided on a single rear locker. Why not another up front? Two reasons. First, this damn thing is now worth roughly ten times what I paid for it all those years ago, so I’m a bit more careful about where I take it. I think full traction on three corners is all I’ll need. Second, and probably more important, I still have the factory non-power steering, and a locking diff in front with manual steering would be, if not actually dangerous, stupendously difficult to control.

I took it for granted that with 320,000 miles on it, a fair amount of which was pulling trailers holding, at various points in history, a 21-foot sailboat; sea kayaks plus gear, food, and water for six clients; and cargo trailers ferrying Expo equipment, the diff would need a new ring and pinion gear, if not spider gears as well. Not so, said Bill—they were still in excellent condition. He replaced bearings and seals and called it good. An ARB High Output compressor in the engine compartment will double for tire inflation, saving precious cargo space I used to have to devote to a portable unit. I voted for installing the two switches in the dash, but Bill whined so piteously about sawing two rectangular holes in my unspoiled dash that I let him put them in the overhead shelf that houses the two-meter radio.

I’m now looking forward to quite a transformation in the faithful Forty, given fresh power, reworked transmission, and 50 percent more traction. It will be on its way back to Arizona in a few days.