CVT belt slippage will likely happen to anyone owning an ATV sooner or later. While as frustrating as it might be, there is often no reason to let it ruin your day.
A wide variety of reasons may be causing it, where most of them are just a normal part of owning an ATV. Other times it may be a sign of severe damage to the clutches and expensive parts may be needed to fix the issue.
I recently experienced belt slippage on my own bike (Polaris Sportsman XP 1000). I was out trail riding with some friends when we decided to go up a small river. The water in the river was only in the ballpark of 15-20 inches deep. I expected my trusty Sportsman would have no problems handling it.
After riding in the water for about 5 minutes, the bike suddenly started losing its forward momentum. I barely was able to get it on shore with the little that was left.
It turned out water had gotten into my belt housing, causing the slippage. Luckily I had brought some tools and was able to drain all of the water. This fixed the issue, and after some laps in moderate speed on dry land, it was ready to go as normal again.
Out of interest, I decided to do a little more research on the subject as soon as I got back home. It turns out water is just one may potential causes to why this is happening.
Cause 1: The belt is worn past its serviceable limits
What many don’t realize is that ATV belts (the belt in your CVT, continuously variable transmission) are indeed meant to be a serviceable wear item on the bike. Over time it will wear, and eventually, it needs replacing for the bike to function properly.
There is a variety of reasons why the belt wears out. Causes like excessive heat or poor riding style will greatly shorten the life expectancy of the belt. These will be covered further down in this post.
Simply high age or high mileage is another common cause. If you see any cracking inside the cogs when you remove the belt and bend it backward it’s time to replace it.
Also look for any chunks missing. If so, you have no other choice than getting a new one.
Over time the aramid cord within the belt will gradually lose its strength and adhesion, and you’ll get what’s known as flex fatigue.
If you start losing top end power, this may be a sign of your belt starting to wear thin. You should find your belts minimum width in your service manual.
Remove the belt and use your calipers to measure the width in three different places. This will ensure a correct reading, and you will also be able to tell if the belt is evenly worn or not.
If the reading you get is below the stated minimum, it’s beyond its serviceable limits and needs replacing.
Cause 2: The belt has become wet
Another very common cause of belt slippage is the belt somehow becoming wet. The water will greatly reduce the friction between the belt and the clutch sheaves, leaving the whole transmission pretty much useless until it gets dried up again.
If this happens, and the belt starts slipping, it is important you do not just give it full throttle trying to compensate. The spinning will create immense heat in just one spot, creating permanent damage to the belt.
You need to remove the moisture before you can drive any further.
The belt-case is made to prevent water from getting inside, but cannot be considered completely waterproof.
Your belt cover will have a rubber seal, but if it is somehow damaged, twisted or in some other way not seated properly, water will get inside.
Errors like these will from time to time slip through the factory quality control. A simple refitting of the gasket may be all it takes to fix the issue.
More common is water or snow entering the belt housing through its air inlet or outlet.
These ports need to be there for proper cooling of the CVT, and even though the manufacturers have improved the design of these inlets over the years they won’t cope with every situation.
Even if you ride in shallow waters, water may splash and get sucked in if you ride too fast when you hit the water. Low speed is the key when riding in water or powdery snow.
Also riding in low gear will allow you to keep the RPM’s up, optimizing the airflow out the exhaust port on the casing, preventing water from entering by blowing it out.
If you really wish to make your bike into a submarine, installing a good snorkel kit to extend the inlet and exhaust port will be your best bet.
Another way water can get in would be if you are unlucky and punch a hole in the CVT housing itself. Riding in areas with a lot of dry branches increase this risk. The housing is often just made out of plastic so it can be broken.
This happened to a friend of mine. He found no issues with the seal, but when he removed the cover he found a one-inch hole straight through it. If the damage is not too bad, some strong sealant will patch it right up again. Alternatively, you can always get a new cover.
And finally, you have situations like the one I told about at the beginning of this post. When I got back home I noticed that some on the bolts on the CVT housing had started to come loose, creating a small gap where water would enter.
I simply needed to tighten these bolts and will keep an eye on them in the future. If the problem reappears I will use some Loctite on the threads of the bolts to keep them in place. Do not over tighten these as this will rip the threads of the plastic housing.
What to do when the belt gets wet?
Regardless of what caused water to enter the housing, you need to drain it. On the bottom of the housing, you will find a drain plug that can be removed. On Polaris bike, this is a red plastic plug.
Let the case drain completely before you start the bike again. Let the bike idle for some time in neutral to let the fins on the clutch do its job. You can even rev it a little to speed up the process.
The airflow from the venting system will gradually dry up the belt and clutches. In just a couple of minutes, you should be able to gently start riding again.
Start at low speeds with little power to let it dry completely. If you hammer it right away it will start slipping, potentially damaging the belt in just a matter of seconds.
Cause 3: Damage to the inside of the clutch sheaves
With the belt removed, check for any grooves, nicks or other damages to the inside of the sheaves. This will wear the belt prematurely and needs to be addressed.
In some cases, the damage can be repaired, and in other cases, you simply need to get ned clutches.
Cause 4: Something disrupting proper belt cooling
If you smell or feel your belt slipping at speed, it could be possible that your belt is heating up and not cooling properly.
Ideally, the bike should be able to keep the belt cool with its belt housing cooling system. And it’s actually a rather simple system.
The fins on your clutches will suck cool air in the inlet port on the belt housing where it’s being blown directly to the primary clutch before its being pushed out through the exhaust by the secondary clutch.
If something is disrupting this airflow you will soon start to experience issues with belt getting too warm and you’ll get belt slippage.
Start by having a look at the exhaust port. If it’s full of mud a simple cleaning will fix the heating issue. Also, have a look at the intake port to see if anything is blocking it.
Over time the rubber in a belt running too hot will start hardening until eventually it will crack and the cogs will peel off. This happens much sooner when the cooling is not functioning properly, so checking up on it regularly may be a good investment.
Cause 5: Black haze on the clutches
If you’ve ridden some time with the belt too hot you should inspect the surface of your clutch sheaves. If you can see something that looks like a black haze on them, this will be belt residue from previous belt slippage or even residue from normal belt wear.
This needs to be removed otherwise your belt is going to continue slipping. Even putting on a new belt will be useless before you get this stuff removed.
Use Scotch Brite pad with some alcohol or acetone to rub it all off. If this does not work you can try with some very fine sand-paper. In a worst case scenario, you may have to replace your primary or secondary clutch.
Do not use brake cleaner as a detergent as this will negatively affect belt performance.
Cause 6: Broken spring in the secondary clutch
If the bike does not want to take off smoothly but is jerking away, almost like its slipping and then act like as if it’s shifting gears, it may be because of a broken spring in the secondary clutch.
You need to take off the belt cover and inspect the spring. If the spring is broken it needs replacing.
Cause 7: You’ve got the wrong belt installed
If you’re experiencing belt slippage after installing a brand new belt, you may have gotten the wrong size. Just a small difference in dimensions can affect its performance.
The difference can be hard to spot with just the naked eye, so make sure you compare the specific model number to your bikes required belt dimensions before you purchase.
If you do intend to use this kind of belt each time you change it, you can use shims to alter the setup of the clutches.
Cause 8: Installing bigger tires
One of the first upgrades many do to their bike is installing a set of bigger mud tires. By doing so you need to remember that it will affect how the clutches operate at different speeds.
The clutches will operate less efficiently, which creates more heat, that in turn may lead to belt issues.
This can be prevented by installing a clutch-kit that allow the clutches to operate efficiently with your chosen tire size.
Cause 9: Heavy towing, or riding in mud/snow in high gear
Another common rookie mistake is using high gear range when towing, riding up steep hills, riding in snow or in deep mud.
Doing so will burn the belt in no time, and as soon as you start smelling burnt rubber you know it’s time to slow down.
Using the low gear range in situations like these will allow for better cooling because of the higher RPM’s, and will allow the clutches to fully shift where they will get a better grip on the belt witch itself will result in lower heat and better momentum.
Cause 10: Belt is burned
Too much heat will burn the sides of the belt, creating a shiny glazed look. This can happen to the whole belt or just to certain spots.
When the belt has gotten one or more of these burnt spots the bike won’t take of without a significant jerking sensation. You will also smell burnt rubber and maybe even see some smoke.
To avoid this from happening you need to do whatever it takes to keep the belt cool.
After some really hard riding its a good idea to put the bike in neutral and rev the bike for some seconds to cool down the metal clutches. This will prevent them from continue cooking the rubber in the belt after the bike is turned off.
After a hard pull through the mud, the last thing you want to do is to just shut off the bike as the remaining heat in the
Cause 11: The clutches are out of alignment
If the drive and the driven pulley is not aligned up properly you may experience belt slippage and other performance issues.
The clutches can be aligned using a model specific alignment tool and procedure. For Polaris bikes, the tool you are looking for is one named the “offset alignment bar”.
In addition to the tool, you will need to get your hands on a service manual if you wish to perform this procedure yourself.
Cause 12: Bad clutch bearing
If a bearing inside the pulley system has gone bad it may cause the pulley not to release the belt.
Grip the clutch firmly with your hands and push it in any direction to see if you feel any slack. If you do, it might be time for an overhaul.
Cause 13: Belt is not broken in correctly
A common rookie mistake some doo as soon as they get the immense power of a new ATV between their hands, is hammering the throttle before the belt is properly broken in.
They do not realize that this is a surefire way to ruin the brand new belt in no time. The belt will burn and you’ll get belt slippage.
All new belts need to be broken in properly to ensure proper belt performance and a long life.
This will be a good procedure to break in the belt:
- Start by cleaning the belt with soapy water before you install it to remove any grease and oils from the manufacturing process. Let it dry completely before you install it to the bike.
- With the belt installed, bring it up to normal operating temperature by running through the entire shift range, all while never exceeding 3/4 throttle. This will take about 15 mins of conservative riding.
- Shut down and let the belt cool completely. This may take about 30 minutes.
- Repeat step 2 and 3 once more. Now you are ready to start shredding the trails!
Cause 14: Mud, sand or other debris in the CVT system
ATV’s are meant to be ridden in really dirty conditions. But if you’ve been pushing the limits a bit too much, or if your CVT housing is not properly sealed, you may have gotten sand, mud or some other debris inside that is interfering with the proper function of the clutches.
Have a look at the air intake or exhaust port to if they somehow have come partly loose, enabling dirt to enter. Any loose tubes need to be refitted properly.
Symptoms of a dirty CVT may be that the clutch will not engage until on higher rpm’s than normal, jerking, belt slipping, before it catches and goes.
When this happens, a proper cleaning is likely all you need.
Start by removing the cover and the belt. This would be enough to get a decent result, using some engine degreaser and a pressure washer to clean everything. Let dry before you reassemble. Try this first to see if it fixes your issue.
If it does not, a deeper cleaning may be necessary.
You will then need to remove the clutches and disassemble them for further cleaning. You will in most cases need a special tool to disassemble your specific clutch.
PS! Be aware that the spring inside may be under great pressure that needs to be released using the proper tool before the clutch can be disassembled safely. Different brands use different tools to achieve this.
If you are not comfortable doing this on your own, any dealer should have the tools to quickly take the clutch apart so that you can clean its insides as well.
Remember to put grease on the bushings, and a drop of oil on the rollers before you reassemble.
Cause 15: Worn or stuck rollers
Inside the primary clutch, you will find three or more rollers that roll up and down the helix when you increase or decrease the engines RPM’s. This is the mechanism behind the clutch sheaves moving apart or together according to how much throttle you apply.
Over time, these will wear out. Any issue preventing them from rolling freely may result in a clutch that is not functioning properly.
You may get belt slippage because the sheaves won’t be able to make proper pressure in the belt, or it won’t have the necessary range of motion needed to function in higher speeds.
I had this issue on an old snowmobile once (the same principals applies to ATVs with CVT systems). It would work fine in the lower gear range, but as soon as I pushed it a little in the higher gear range, the belt started slipping.
I disassembled the clutch and found the rollers were badly worn on one side. So after a good cleaning, and greasing (on all the right places), and a brand new set of rollers, the clutch was as good as new. No more belt slippage.
Cause 16: Worn helix or clutch bushings
This cause is in the same ballpark as issues with the rollers. If the helix is somehow damaged or worn, the rollers will not be able to roll freely up and down as they are supposed to. Look for any cracks or burrs that should not be there.
Sometimes the whole thing will blow up into pieces, leaving you completely stranded.
When you have the clutch disassembled you should check the bushings in the secondary as per the service manual.
Symptoms of a bad ATV belt
Loss of performance can be a sign of a bad ATV belt. If you see cracks when you bend the belt backward, if chunks are missing or if the belt sides have a glazed look, it is bad and needs replacing.