Ask The Editors: Give ATV Differential Options To Me Straight
Digging into the world of gears and shafts.
There are AWD which are really 3 wheel drive machines. These will not have an actuator.
There are AWD with a locking front differential for a true 4 wheel drive. These will have 1 diff lock actuator.
There are 2 mode 4×2/4×4 drive machines. Of these some have 1 actuator to switch between 4×2 and 4×4. There are some with 2 actuators to switch between 4×2/4×4 and also lock the front differential.
Are the above all the possible combinations?
Is the 4×2/4×4 actuator always located on the differential itself, meaning the front drive shaft is always turning when the rear shaft is turning?
This is a very good question – one that we encounter in various incarnations at least once a month (albeit not always so technically direct). The reason, we suspect, is because like in the automotive world, there are nearly limitless combinations of technologies at each manufacturer’s disposal to achieve the end result – getting all four wheels turning at the same time.
As such, there are exceptions to almost every rule, but for the most part, this is how it shakes down. AWD systems do in fact distribute power to all four wheels of the machine but they do so through a single speed transfer case. What this means is that the rider has less manual control over the power distribution.
Modern systems use wheel sensors and fast computers to determine which wheel is suddenly experiencing increased RPM relative the others (AKA slipping) and then distributes drive connectivity accordingly. The advantage to these systems is, of course, fuel economy and “set it & forget it” ease of operation.
Most 4x4s differ by implementing multi-speed, manually select-able transfer cases – where the default setting is driving the rear wheels only (2×4 mode), with the option to activate the front wheels resides entirely with the rider. Years ago these transmissions were often cable-actuated/ manual engagement. These days, the process is typically accomplished through “fly by wire” technology: the press of a button tells the quad’s computer to initiate the actuators to engage or disengage the front wheels accordingly.
The locking differential works simply by locking the two front axles together so the drive torque is distributed evenly between both wheels/ each spins at the same speed. In short, it eliminates traction availability from the equation and simply turns both wheels no matter what lies in your path. End of story? Not quite. Companies like Can-Am offer a limited slip differential, which, as the name suggests, can distribute the power to whichever wheel calls for it even when locked. This way, things like turning isn’t a bear. You can learn more about that design here.
As for your specific question as to whether the front driveshaft is always spinning, even when 4×4 is not engaged – the answer is… It depends, of course. Like we discussed above, there are many ways to skin the proverbial cat with these systems. In the late 90s – Honda offered a system whereby both the front and rear driveshafts always spun, and when 4×4 was selected, actuation took place when the hubs engaged the shaft.
This isn’t the only option, though, as there are also other successful designs on the market – like an actuator that connects the shaft via transfer case rather than by locking hubs (in which case, the front shaft would not spin until called upon).
You have the right idea, though, in your query – there are many different systems out there and everything you mentioned does exist. The best advice is to simply look up how the system works on the make/ model you are considering if in doubt. Most brands go to great length in their product brochures and online schematics to demonstrate to you, the potential buyer, why their particular configuration is the best.
