Looking Back At The Automatic Clutch

The CVT reigns supreme.

These days almost all of our ATVs comes in one of two configurations as far as transmissions go. You either have a fully automatic CVT system or you have a fully manual 5-speed setup.

They are distinct because they operate at extreme ends of the spectrum. In the automatic corner a belt positioned between two cones pointing in opposite directions can mimic just about any gear ratio imaginable instantly, all without any input from the rider (well aside from perhaps how hard he’s pushing on the throttle).

On the manual side you have a left-side handlebar-mounted clutch lever and a gear shifter next to your left boot. Just like a fully manual transmission in a car, you are responsible for engaging and disengaging the drive train as well as determining the correct gear for the given situation. These days the fully manual setup is mostly limited to the few remaining performance ATVs on the market but remains the proper setup for MX racing.

Would it surprise you to learn that neither of these options was the dominant transmission setup in ATVing until fairly recently? The first 20 years of the sport’s life used a system that was a dash of both and yet neither. Sadly it has all but gone extinct now.

The Semi-Automatic

The semi-automatic or, more correctly labeled, automatic clutch was the go-to design for nearly all ATVs from the 3-wheeler days onward. They gave the operator more control (and responsibility) than a fully automatic system but weren’t quite so steep to master as a full manual transmission.

The automatic clutch essentially frees the rider from ever having to worry about a clutch lever. In fact, there wasn’t one. With this setup you could come to a complete stop in gear without stalling the engine. Then, to get going again, you simply tapped the gear lever with your left foot back down into first and got back on the throttle.
There was no need to feed a clutch out to get back underway.

However, this was still no automatic transmission; you are responsible for shifting the machine from gear to gear like with a manual. However, to shift, you simply let off the throttle, clicked the shifter up a gear and got back on the gas.

How Did They Work?

The way these transmissions worked was pretty genius as well. Whenever anything is spun, centrifugal force wants to pull the center outward. This is why you can, with enough speed, swing a bucket of water over your head without getting a drop on you.

Capitalizing on this law of physics, engineers designed a clutch with pawls that weren’t fixed in place, but instead could extend out when the shaft spun. When you got on the gas, this shaft began to spin – until those pawls expanded and grabbed an outer drum, spinning that as well.

This outer housing (drum) is what turns the driveshaft/ drive chain sprocket. So as long as you were on the throttle, you were moving.

Let go of that throttle, however, and the shaft would instantly stop spinning. Those pawls, which were on springs, retracted tightly into place and, of course, that outer housing was no longer being driven. You were, in essence, coasting with the clutch engaged whenever you let go of the throttle.

You could now shift up or down or even just slam on the brakes. The engine was fully disconnected from the drive-train so long as you weren’t still on the gas.

What Happened To Them?

While it’s true they offered the operator more control over a fully automatic setup, they also came with a steeper learning curve. Many would-be riders found out they had to shift gears and lost interest even before the test ride. In short the appeal of the fully automatic CVT (continually variable transmission), that worked its way into the ATV scene from our snowmobiling cousins, offered all of the performance without the intimidation factor.

We suspect the automatic clutch, despite doing everything right, will never make a large-scale come-back as it no longer serves any practical purpose. Performance purists still have full manual transmissions to work with and the masses are quite content with the easy of operation of the CVT fully automatic system.

They can still be found on occasion, especially on off-brand and department-store minis but their time in the sun is mostly relegated to the entire 1980s and first-half of the 90s.

Did You Know?

A third type of clutch system also exists that has also fallen out of favor in recent years. This one, called a slipper clutch, was never offered from the factory but rather was (and still is) an aftermarket option for a very specific type of rider.

Upon first glance, slipper clutches sound a lot like the automatic clutch but they are different. These automatically engage the clutch when the machine starts to rapidly decelerate. Then, after that rapid deceleration levels out, the clutch disengages and again and it’s back to a full manual transmission. In other words, if you were to keep slowing to a stop without pulling the clutch lever, you will stall.

Why would anyone want this? Well, in racing sometimes square edge obstacles like ledges or successive mounds (whoops) can catch the real wheels and stall the engine if it’s pushing a high gear. Also slamming the brakes to lock up the rear end of the machine to corner can cause a stall at best, force the whole back-end to hop at worst because of torque tugging on the rear shock.

Having the engine coast with the clutch engaged briefly in these moments can improve handling during hard throttle chops.