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Month: November 2022

Rebuilding a CVT Clutch: The Basics

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Most of today’s ATVs use a constantly variable transmission (CVT) clutch system.  While they vary by manufacturer, the basics of a CVT clutch are essentially the same.

The two sheaves of the primary clutch are spread apart from one another because there’s a clutch spring within the assembly pushing them apart. The primary clutch assembly is directly attached to the crankshaft, so as the engine runs, the rotation of the crankshaft causes the assembly to rotate with it. As the engine speed increases, the RPMs increase and the speed to which the primary clutch rotates also increases.

As it rotates faster, the primary clutch generates centrifugal force on those weights, and they begin to overcome the force of the clutch spring. When the force of the spring is overcome, the outer sheaves move inward toward the inner sheave. This movement pinches down on the belt, engaging it, and transferring the rotational power from the primary clutch to the secondary clutch.

As mentioned, each manufacturer’s version of the CVT clutch is different, but they all basically work the same way. If the sheaves won’t move and push and pull the belt in or out, it might be time to rebuild the clutch. Watch the video above and follow the steps below for the basics of how to rebuild a CVT clutch.

Tools Needed – CVT Clutch Rebuild

  • Ratchet and sockets
  • Torque wrench
  • Primary clutch drive puller (specialty)
  • Clutch drive compression tool (specialty)

NOTE: We used a 2011 Polaris Sportsman 850 XP CVT clutch for reference, but the CVT clutch system on other ATVs will be very similar. The main differences are the specs, so refer to the service manuals for your ATV. You might also need different specialty tools if you’re dealing with a different ATV make and model. 

The Basics of Rebuilding a CVT Clutch

Step 1. Remove the wheel and the clutch cover.

NOTE: On a Polaris Sportsman 850, you need to remove a frame strut first to get to the clutch cover. 

Step 2. Remove the drive belt.

NOTE: Watch the video above to see the process of removing and replacing the drive belt on a Polaris Sportsman ATV. 

Step 3. Remove the secondary clutch assembly.

Step 4. Remove the primary clutch assembly by first taking off the primary clutch bolt, then using the primary clutch drive puller to break the primary clutch assembly free from the housing.

NOTE: The bolt holding the primary clutch on this particular model has a reverse thread, so you need to turn it clockwise to loosen it.

Step 5. Inspect the drive belt by running your fingers along each side of the belt, feeling for any uneven patches or wear. Check the belt’s teeth for any that may be cracked or damaged, and examine the overall condition of the drive belt. A healthy belt feels flexible; an older belt feels dry and stiff.

Step 6. Inspect the sheaves by running your fingers across the faces of each sheave to make sure they’re perfectly smooth, with no grooves or channels dug into them. Each sheave should be a bright metallic color, so if a sheave is darkened or discolored, it’s glazed and may need to be replaced.

PRO TIP: Before replacing a glazed sheave, try using contact cleaner and an abrasive cleaning pad to knock off the glaze. This gives the belt a clean, lightly scuffed surface to bite into. 

Step 7. Take the primary clutch apart by using the clutch compression tool to keep pressure on the clutch spring so that you can remove the outer plate.

PRO TIP: Before taking the primary clutch apart, mark where the outer plate is in relation to the inner plate. They’re balanced, so marking them helps ensure they’ll be reinstalled in the same orientation.

Step 8. Replace the weights if necessary. If you have to replace the weights, make sure to purchase identical weights to those already installed on the clutch. This is because most manufacturers design their CVT clutches to fit multiple models, and each of those vehicles has a slightly different clutch setup, so the clutch will require vehicle-specific weights and spring.

PRO TIP: If you have to replace the weights or transfer them from an old clutch assembly to a new one, install new shoulder bolts and flex lock nuts on each of them. They’re inexpensive, and fitting new ones gives you peace of mind that they’re working perfectly once you put everything back together again. 

Step 9. Reinstall the CVT clutch by simply reversing what you did to take it apart.

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Alternative method to Bleed the ATV Master Cylinder

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Alternative method to Bleed the ATV Master Cylinder

A variation of the above methods is when you, instead of controlling the fluid stream with your finger, use the banjo bolt as a bleed valve.

This is how you do it:

1. Open the brake fluid reservoir lid and diaphragm. Be careful; the bolts strip easily.

2. Pour new brake fluid into the reservoir so that it’s at the maximum level mark.

3. Place plenty of rags to soak up the brake fluid being bled.

4. Pull back the rubber cap covering the banjo bolt.

5. Then pump the brake lever as you do when manually bleed the brakes.
6. But instead of opening the bleed valve by the caliper, you open the banjo bolt until the brake fluid starts sputtering out.

7. Tighten the bolt when the brake lever is about 80% engaged.
8. Re-apply pressure and open the banjo bolt again.
9. Continue until you get a sputter-free stream of brake fluid.
10. Then bleed the brakes normally. You should now be able to build proper pressure.

This method may be a bit messier, so make sure you use plenty of rags to keep your ATV protected.

Yet another alternative method – directing fluid back into the reservoir

You’re probably starting to realize there is almost no limit to how many ways you can bleed the brakes on an ATV. Here is another tip to try.

Instead of letting the brake fluid squirt out of the banjo bolt and down onto a rag, you can direct it back up into the reservoir. Insert a piece of clear tubing into the outlet port on the reservoir and put the other end of the tube down into the master cylinder.

Make sure it is completely submerged at all times. Then start pumping.

Continue until you see only clear brake fluid inside the clear tube. When you are done, install the banjo bolt quickly, so as little air as possible gets into the system. Top off the brake fluid reservoir and leed the brakes as normal.

Bench bleeding an ATV master cylinder

The expression “bench bleeding” comes from removing the master cylinder off a car and bleed it on a workbench.

On an ATV, you don’t actually have to physically remove the master cylinder from the bike to “bench bleed” it, It is just as accessible where it is sitting on the bike.

It’s actually faster and easier to bleed it when still attached to the bike, but you run a small risk of spilling brake fluid on the ATV. Brake fluid is corrosive and will damage paint and plastic.

Another benefit of bleeding the reservoir on the bench is that you are free to rotate it so that the outlet port can be facing upwards when you are done bleeding.

This way, you can better prevent air from getting back into the system during installation. The banjo bolt can be installed with the port still facing upwards before fastening the master cylinder to the handlebar again.

Ultimately it is up to you whether you want to bleed the master cylinder when still attached to the handlebar or if you want to remove the whole assembly and perform the job over at your workbench.

Tools required:

The same tools as the first method. Also, you need the proper tools to remove the master cylinder from the handlebar. This varies between the brands and models of ATVs.

This is how you do it:

The procedure is pretty much identical with bleeding the master cylinder when still attached to the bike. But before you begin, you need to remove the whole assembly from the ATV.

  1. Pull back the rubber cap covering the banjo bolt.
  2. Place a rag underneath to soak any spilled brake fluid.
  3. Open the banjo bolt using the wrench.
  4. Then proceed to remove the master cylinder assembly from the bike and moving it to your workbench.
  5. Secure the unit in a vice, but do not overtighten. The material cracks easily.
  6. Bleed the master cylinder as described in steps 6 to 11 from the first method in this post.
  7. When you are done with step 11, top off the reservoir with new brake fluid and reinstall the cover.
  8. After reinstalling the cover, rotate the assembly so that the outlet port is facing upwards and move it over to the bike.
  9. Install the banjo bolt with the outlet port still facing upwards.
  10. Then reassemble the master cylinder to the handlebar.
  11. Finish off by bleeding the brakes as you normally would.

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What is an ATV?

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At its simplest, an all-terrain vehicle (ATV) is defined as a vehicle with the following: a straddle seating position, handlebar steering, and the ability to maneuver through a variety of terrain conditions. While there are a variety of ATV customizations and modifications available, at their base all ATVs share those three features.

Wheels and Tires

ATVs have either three or four wheels. Tires are kept at a lower pressure than standard car or UTV tires.

Steering

The operator can steer the ATV by using handlebars.

Seating and passenger capacity

On an ATV, the operator is seated in a straddle position. ATVs are normally built for just one rider, some are made to carry the operator and one passenger.

Speed and handling

ATVs are not “one-size-fits-all” and should be sized appropriately for the operator.

When operated safely and correctly, ATVs offer a quick and nimble means of transportation over a variety of terrain.

Braking and acceleration

The majority of stock ATVs come with a thumb throttle. Pressing the throttle with the thumb controls acceleration. It is possible to modify an ATV to use a twist throttle, which allows the operator to control the vehicle’s acceleration by twisting the ATV’s handle.

Given the unpredictable nature of the terrain ATVs cover, twist throttles can make it difficult and dangerous to control the vehicle. For example, if a rider leans forward and unknowingly twists the throttle while going downhill, the vehicle may unexpectedly pick up speed. This can easily cause the rider to be thrown forward off of the vehicle, and the vehicle may roll and fall on the rider.

To brake, operators can use either the brake handle or the foot pedal, depending on what type of ATV they are operating.

Safety equipment

ATVs often do not come with safety equipment as part of the vehicle. Some do have “roll bars”—strong steel pipes that form a cage-like structure around the operator to provide protection if the vehicle rolls.

ATV operators should strongly consider wearing protective clothing, boots, and gloves—and should always wear a helmet.

Cabin

ATVs are open and do not have a cabin. However, as mentioned above, some do have roll bars.

Uses

As a quick means of transportation over rough ground, ATVs are a valuable tool. However, they are mainly used for recreation, like racing or trail riding.

Cost

Compared to UTVs, an ATV is a much more budget friendly option. When planning their purchase, potential buyers should make sure to account for the additional costs of safety gear and insurance.

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