Understanding the Autotranny (belt)

[rundrave]

Heres a little info I came up with which will hopefully help some of you understand the belt concept. I know alot of people are curious as to how they work on different makes an models.

The CVT (Continuously Variable Transmission) consists of a belt and 2 pulleys, each change width to change the gearing. Engine rpm, wheelspin and load determine the gearing. For lower gearing, the front (drive) pulley widens and the belt rides low, while the rear (driven) pulley narrows and the belt rides high.

The theory behind all belt drives is the same. The drive and driven pulleys adjust their diameters to fit rpm and load. It is in the details, in how they are different.

The polaris system, while at idle and in gear, has the drive pulley open far enough for the belt to go slack. This allows it to idle in gear at a standstill, but causes separate problems, related to engine braking. There are notches in the belt, and those notches grab the indentations in the drive pulley, when the pully opens up at idle. It will provide engine braking, but not instantly, at throttle off. And because the pulley opens, and the belt is slack when going power on, the drive pulley suddenly closes, on the belt, and because of the mechanical advantage of gearing, can be tough on belt life if the tranny is in high. Thats why its recommended to be in low, while doing slow driving, the mechanical advantage of lower gearing, allows the pulley to grab the belt, with less slipping and heat and wear.

This is one of things that bugs me about mine, I only have a high gear not low, when racing and going down a steep hill I usually coast with the breaks on and no throttle at all, when I get over a rough spot and its safe for me to accelerate, when I hit the trottle and the belt grabs to the engine breaking, it puts some stress on the belt but nothing I am going to worry about, just one little pet peeve of mine, took a while to get used to it. But I also dont have to worry about the engine breaking me slower than I want, I can coast as fast I as please.

The duramatic(suzuki) and ultramatic(yamaha) are very similar, to each other. The belt on these are always in tension on the drive and driven pulley. It never goes slack. Which means, the only time you go to low range is when you want to. Theres no requirement to be in low range for going slow. Theres no sudden gripping of the belt , with power on, and no heat and wear either. There is a centrifical clutch, on the end of the crankshaft, which disengages the drive pulley at idle. This lets it idle in gear at a stop. The centrifical clutch only works when power is on. For engine braking, there is a clutch, which is a one way clutch. In one direction, it free wheels(power on), and when the tires drive the motor(power off), it provides the link to give almost instant engine braking. Belt life is higher and noise is less with either of these two trannys.

The artic cats with suzuki motors, have the duramatics, and the 650 has the kawi system(I think). The problem I have seen with these is after a high speed to zero stop. If you don't ease back into the throttle, before accelerating, the clutch makes a howling noise before engaging.

On the Yahama you can put the tranny in neutral and rev it up, on the Polaris when I rev it up the whole machine vibrates because there are alot of moving parts. The Yahama is in true neutral and the engine free revs, the polaris doesnt free rev as its turing everything.

But in hindsight if you ever get the system wet, get it on a dry area, pull the plug, drain it and start it up, and rev it in neutral. The spinning and the air flow, in the tranny dries things out, without putting a load on the belt. If you were to just try driving away, the wet belt will do slipping, and glazing, and wearing, because of the load, on the belt and pulleys.

Bottom line I think today's autos ain't the Polaris' of years ago slipping etc,I think belt drives are hear to stay. I would rather change a $40 belt than something that costs alot more, clutch/tranny.

[jltimm]

Thanks for the well explained info on the belt systems.I don't think many people even know about the differences in each system?

[Eiger0304]

Do you have an explaination for the wet vs. dry clutch? Uncle has a Grizz 660, while riding it once, he filled up his clutch housing with water. We drained out and let it sit for a while. Upon getting under way he could only get the Grizz to go 40 mph. After returning home we pulled it and found grease everywhere. To make a long story short, it cost about $100+ for a new belt (kevlar) and 2 hours of cleaning. Not sure why it happened, just want to prevent it from happening again.

By the way, nice post.

[deepportage01]

are you sure it wasent belt dust and water mixed that also looks and feels like grease.

[CraigM]

He must have gotten pretty deep to fill the clutch with water. I have had mine up to the seat and not had that problem. Yamaha clutches use about a table spoon worth of grease on the rollers and thats it. I'm guessing the reason it would only go 40 was all the gunk that got in there not letting the rollers move all the way. Would have been an easy cleaning to fix.

[Eiger0304]

Not really sure what it was. Took it to buddy that works for a local ATV place and he said it was grease. It took him about 2 hours to clean it out. The belt is basically shot after this happens. After thinking about it some more, I believe my uncle tried driving before the belt housing was drained. Again it was an '05 Grizz 660. I seen it myself and there was definitly grease. Not sure were it came from. Just curious if someone knew.