Tales From the Bench - June - 2019

Handle With Care: CVT Belts

CVT transmissions are becoming a more and more common site in shops today. As a result of this, we’ve started to see more broken CVT belts. Many times, the customer would come into the shop for normal maintenance and with-in days returned with a broken belt.

We’ll be discussing the basic design of the CVT belts and how to avoid damaging them during the repair process. Many manufacturers offer CVT transmissions with belts, including Nissan, Dodge, Jeep, Mitsubishi and Honda just to name a few.

Belt Components

The Pushbelt, in figure 1, is produced by Bosch and consists of elements that can measure 24mm, 28mm or 30mm wide. There are also two sets of rings per belt. Sometimes these rings are referred to as bands.

Each ring is 0.008” thick, with 6 to 12 rings per side considered normal but the number of rings per side can vary. The higher number of rings offer a higher torque rating for the transmission. Flipping the rings over or swapping sides is not recommended. Each ring in the pack is a different size, with the innermost ring being the smallest and the outermost being the largest.

Belt Condition

Both, the sides of the elements and the condition of the rings, determine if the belt can be reused (figure 2).

Let’s talk about the sides of the elements first. You should always be able to see consistent lines in the element. If you see smooth areas or metal piled up, you need to replace the belt. The same can be said if the belt is smooth all the way across.

When checking the condition of the rings inspect the sides of the rings, there should be no signs of contact. The rings can be dented if the belt is mishandled (figure 3).

Lay the belt on its side and remove the ring pack for inspection. Make sure to keep the rings in order and do not flip them over. Inspect the rings for cracks or dents. Look at each ring pack one at a time and then reinstall them. Flip the belt over and inspect the other side. Keeping everything in order is essential; this will help ensure that everything goes back in correctly.

Belt Handling

Damage can occur by squeezing the belt together (figure 4). If the belt is squeezed together too tight it stresses the outer ring. This also binds the rings on the sides of the element grooves.

Twisting these belts also needs to be avoided. When twisted, stress is put on the corners of the ring pack because they are contacting the elements (figure 5). This dents the rings and will cause the belt to break soon after, even under normal driving conditions.

The most common way of damaging a CVT belt is by separating the belt from the pulleys during the pulley removal.

When removing the belt from the pulleys you need to use the proper tools to take all the pressure off the belt. You don’t want to twist the pulley out when there is pressure on the belt. When you twist the pulleys out like this you may dent the rings because the pulley contacts the side of the rings. Dented rings will break soon after put in operation. If the pulleys are twisted out, like in figure 6, you can count on seeing the transmission back on your bench with a broken belt.

One helpful tool you can use is to apply vacuum to the secondary pulley to get it to separate and take tension off the belt. When the pulley is in the open position you can install a tool to keep the pulley separated. If you do not have a tool you can make one by cutting a wide bushing in half to make a moon shape.

Install the half moon shape bushing in between the pulley to keep them separated, a larger diameter hose makes it easier to perform this task. You want a vacuum pump of 3 CFM or larger.

Do not remove both pulleys from the rear cover if there is tension on the belt. You need to have a puller on the primary pulley to release tension on the belt. Make sure not to twist or put pressure on the belt when removing the pulleys from the rear cover.

If you follow the basic rules of not squeezing, twisting or putting pressure on the belt during pulley disassembly and installation you will have no issues with broken belts.

A special thanks to Coen Van Beek at cvtpushbelt.com for his input on the broken belts. He also makes CVT tool kits to rebuild CVT transmissions. His tools make it easier not to damage the belt during overhaul.