I drive an ’86 VW T3 Vanagon Syncro 7-passenger van (a “tin-top”). It’s my daily driver, work truck, travel camper and off-road excursion rig. Starting in 2011 some fellow Syncro owners organised an annual 3-night jamboree at Moab, Utah, calling it Syncro Solstice (in the early planning discussions it was going to be in late June when school’s out, but a lot of folks weren’t thrilled about the brutal heat of Moab in mid-summer, so late May seemed a better time, damn the schoolkids. But the name stuck, and it’s a good one). I’ve managed to attend every one of these, and it’s always just a ton of fun. There are myriad offroading adventures to be had, but the best part, I gotta say, is getting a posse of Syncros out on Moab’s famous slickrock trails, where there’s always lots of people in tricked-out Jeeps and rented four-trax buggies, and watching those folks’ jaws drop when they see a string of old VW buses come trundling up over some giant mound of sandstone. Someone will invariably come over and coyly walk around the Syncros trying to figure out how this is possible, and finally give up and ask “is that four wheel drive?” I always play them along and say “no”, and enjoy the reaction for a couple beats before admitting that yes, they’re actually factory all-wheel drive VW buses (and the occasional pickup), kinda rare so not surprising they never heard of them.
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Anyway, legend has it the early Mormon pilgrims called the naked sandstone slickrock because it offered their iron horseshoes and wagon tires so little purchase, but for rubber tires it’s anything but; even soaking wet, it’s one of the highest-traction surfaces you’ll ever drive on.
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The Vanagon Syncro is a pretty capable off-road vehicle, considering it was sold as a station wagon, but one thing it doesn’t have a lot of is wheel articulation, which is the ability of the wheels to deflect up and down in a large range relative to the body and especially relative to each other. That means on really uneven terrain, it’s common for a wheel to have very little traction or even to lift off the ground entirely. We get lots of cool-looking photos of Syncros with a wheel or two in the air, which looks gnarly an’ all, but actually is showing off the van’s main weak point when it comes to offroading, because once a wheel leaves the ground, the open differential on that axle spins that wheel ineffectually and the torque going to the opposite wheel on that axle goes to zero, and unless there was already enough momentum to roll over the obstacle, the vehicle isn’t going anywhere.
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Even vehicles with high articulation run into this problem on extremely uneven terrain, and any vehicle can encounter the same problem with both wheels on the ground when one wheel has very low traction because it’s on ice, snow, mud or sand.
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To overcome this problem, many Syncros and other off-road vehicles are equipped with locking differentials, or “lockers”, in one or both axles. By engaging the locker, the two wheels on that axle are locked together as if there was a solid shaft between them, so even with one wheel in the air or on slick ice, the wheel at the other end of that axle still receives full torque and can move the vehicle.
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My Syncro van has a rear locker only. Some have the front too (they were a factory option). Before moving onto a very uneven or low-traction surface, I will often engage my differential lock. But on a high-traction surface like slickrock, any amount of cornering with the diff locked can easily shear a half-shaft or shatter a CV joint, and someone almost always breaks one or the other on our slickrock outings (but being drivers of 30-year-old VW’s far from home, thankfully someone always seems to have a spare half-shaft with CV’s ready to swap in).
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The slickrock trails are very uneven terrain and you need the diff lockers often to negotiate obstacles, so the locker’s have to be turned on and off again and again. The stock locker controls are some vacuum valves on a little subpanel below the dash, so you have to let go of the shifter and reach down to pull the valve on, then push it off, over and over. I found this was really cramping my style, in fact sometimes I really wanted to be able to shift my transmission simultaneously with working the diff lock. At some point while reaching for my locker valve once again I remember saying out loud, “this needs to be right in my hand”. And the idea started growing in my mind.
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I’ll write more about the development rationales in another post. Thanks for reading!