Polaris has been using the same basic Hilliard front differential design in all their Rangers and RZRs since 2003. They’ve only made small changes here and there to make it stronger, make it more reliable, or make it fit new models. Sounds like they’re using some old technology then, right? Maybe it’s time to update? Here’s the thing: they nailed the design back in 2003. It’s pretty close to perfect. Can-Am has made strides to catch up, but they can’t compete with the simple elegance of Polaris’ front diff.
Originally, the only purpose of the differential was to allow your left and right wheels to rotate at different speeds. That specifically makes turning easier where your outside wheel turns faster than your inside wheel because your outside wheel travels a greater distance. If both wheels turned at the same speed, one tire would have to skid and lose traction which is never good.
Modern differentials in UTVs have a lot more to worry about. They deliver power to the front wheels, make sure the wheels can roll at different rates, and lock those wheels together when needed. It’s no small task, and that’s why differentials today are complicated and so different from one another. Can-Am uses a differential design that is completely different from Polaris’ design for example.
Polaris and Can-Am both solve the same problems with their front differentials, but Polaris’ elegant design makes it do precisely what you want it to when you want it to without you having to give it much input at all. To understand what makes it special, we’ll have to break it down first.
Let’s follow the power as it comes into the diff: First, your spinning prop shaft turns the pinion gear of your diff. The pinion gear then turns the ring gear that is wrapped around the sprague and the two hubs your front axles are connected to (more on the sprague in a bit). When your four-wheel-drive is NOT engaged, the power transfer ends there. You hit the gas, the ring gear spins, the sprague spins, the armature plate spins but it doesn’t apply power to your hubs to turn your axles.
When you flip that switch on your dash, all you’re doing is turning on an electromagnet in your diff. All that magnet does is make it harder for the armature plate to spin which makes it harder for the sprague to spin. The inner surface of the ring gear has many peaks and valleys. Normally the sprague and its rollers spin along with the ring gear in those valleys, but when the magnet is turned on, the sprague gets pulled into one of those peaks. The rollers are pushed into the hub and grab it through pressure and friction. With the rollers wedged, the ring gear then transfers power to the hubs, axles, and wheels thus providing four-wheel-drive!
So what? Getting four-wheel-drive isn’t anything special and Can-Am’s Visco-Lok does it just fine. The difference comes in how each of these differentials lock. Locking your differential is key to success in sketchy situations or insane terrain.
Most UTV manufacturers provide an on-demand locking mechanism. Flip a switch on your dash and the front diff locks providing you with tons of extra traction. When you get through the rough spot, just flip it off and keep going. You don’t want it locked all the time because it makes cornering tough, you have less control, and puts extra stress on your differential.
The other kind of front differential is the automatically locking differential. Polaris and Can-Am front diffs both fall into this category. These types of diffs lock automatically through a mechanical or electrical process. The trigger that causes these diffs to lock is slippage of a front wheel—these diffs are sometimes called limited slip differentials—but what sets Polaris apart from Can-Am is the way in which that slippage causes the lock to engage.
Can-Am’s Visco-Lok uses the slippage of a front axle to mechanically operate a pump. This pump adds pressure to a viscous fluid that compresses a clutch pack which locks the differential via friction. This tends to be unreliable because the slipping front tire has to make one complete rotation or more before the diff locks.
Polaris’ diff is completely different. Remember, with 4WD engaged the ring gear uses the sprague and its rollers to turn both front axles. The way it locks is ingenious.
The front diff is geared lower than the transmission which means the front axles have more torque and turn slower than the rear axles. This means that if you’re driving on dry flat ground with four-wheel-drive engaged, the ring gear is turning slower than the front axles which are rolling the same speed as the rear axles. That means the rollers don’t get wedged and no power is transferred to the axles. No four-wheel-drive.
When you hit a tricky section and your back wheels start rotating faster than your front wheels, the ring gear wedges those rollers and your front wheels start rotating with power from the engine. You have four-wheel-drive and your front diff is locked. The time it takes for it to engage and lock is almost instantaneous—the ring gear has to rotate only about 5 degrees.
Here‘s the really cool part, this engaging action can operate on each axle independently. So if you’re turning hard, your outside wheel will be moving fast and not engage while your inside wheel will engage. If you’re off camber in some crazy rock garden, a front tire hanging over open air will force the diff to lock instantly. Any time a front wheel gets caught or slows down at all, the diff is there to give it power. That means it always gives you power exactly when you need it and doesn’t give it when you don’t.
At its heart it’s truly a simple mechanism made up of just a handful of parts and only one electrical input. They work together in complex ways but if you need to replace something or service something, you don’t have to be a professional mechanic to figure it out.
Can-Am now has a competing differential on the market. It’s the Smart-Lok Differential. It solves a lot of the problems that the Visco-Lok has by using an electronically actuating diff locking mechanism. That’s nothing special on its own, but Smart-Lok uses a network of sensors on your machine to automatically lock and unlock the front differential.
It knows your steering angle, your speed, your individual wheel speeds along with your set ride preference and uses that information to lock and unlock the front diff on the fly. It’s cool, it’s innovative, and it works.
The main advantage that Smart-Lok has over Polaris’ diff is the same advantage that all on-demand locking diff’s have over it: Polaris diffs don’t always do what you want them to on ice. If you’re sliding on a sheet of ice, your front diff will lock if you hit the gas at all making it extremely difficult to gain control. Your best option is to turn off four-wheel-drive entirely. On demand lockers like Smart-Lok let you keep your four-wheel-drive without locking if you’re sliding on ice. That’s a much better setup to gain control in this instance.
Older Polaris machines tend to have some weaker parts in their diffs which can lead to failure. Luckily there are lots of upgradable parts you can purchase for cheap (ahem) to get them up to snuff. These days, new Polaris diffs are pretty solid. The only real changes they’ve made over the years have been to make them stronger and more reliable.
The problem is that it’s a Brute Force answer to Polaris’ simpler front diff. That means that right now you can only get them in Can-Am’s highest end Maverick X3s. If you’re not willing to drop thirty-grand for a UTV, you’re stuck with Visco-Lok. All that for performance that is at best a small improvement over Polaris’ age-old design that comes with every machine whether you get a used RZR for $4,000 or a brand-new Turbo S for $30,000.
So, does Polaris have the perfect diff? You be the judge.