The Problematic CVT 7 - Transmission Digest

The Problematic CVT 7

Wayne Colonna breaks down the problematic nature of the CVT 7.

The CVT 7 is perhaps one of my most favorite CVTs. I like the design and simplicity of it and the way it functions.

But is sure does have its problems. The most common ailment it has known to many is the way the secondary pulley speed sensor exciter cage separates from the pulley (figures 1 and 2).

Figure 1
Figure 2

This is a design flaw which due to expansion and contraction of metals, allows for this separation to take place. In all the vehicles that has had this issue, the complaints were very similar. It has a sluggish feeling along with a rattle noise during acceleration. The rattling noise makes sense. The sluggish feeling complaint also makes sense. The sensor exciter cage still rotates with the pulley but not at the same speed as the pulley.

This affects the way the computer tries to ratio the transmission from a launch. To date, I have seen this problem with as low as 65k to as high as 110K +. If careful, this could be an in-car repair. Taking the rear cover off is the tricky part. You first need to have enough room to pop to cover off. And secondly, you must not allow the pulleys to come out of the main case during removal of the cover.

Sometimes this works out well. Other times the primary and secondary pulley shaft bearings fit so tightly in the cover; the pulleys come out of the case when trying to remove the cover. But, if the cover comes off easily, a repair can be made by securing the cage to the pulley. This will require cleaning the cage and pulley, assure that the cage is centered, and then secure it to the pulley with several TAC welds evenly spaced.

Another interesting observation that has been made is the CVT fluid oxidizes rather quickly. It smells burnt and overheated yet not one single friction plate is burnt. Not even the converter clutch is damaged or burnt. This seems to suggest that the heat exchanger is insufficient in cooling the CVT fluid. The CVT 7 has two water pipes on the heat exchanger, an inlet and an outlet.  As the water flows through it, the heat of the CVT fluid should dissipate into the water. The transaction of this process does not appear to be effective. However, with these same transmissions that have this deteriorated fluid, when the pan is pulled, each of the three magnets in the pan is coated with metal particulates (Figure 3).

Figure 3

Yet no damage inside the transmission can be identified. Where this metal is coming from is speculative on my part.  Maybe the gears were not properly dressed. And it is this metal that may have entered the heat exchanger restricting the flow of the CVT fluid to be cooled. Either way, it is recommended to install a new heat exchanger every 30K to extend the life of the fluid and transmission.

Another issue that has come up with this little CVT 7 is a sudden loss of forward movement but still have a very good reverse. The sun gear integral to the Low Brake hub shears away as seen in figures 4 and 5.

Figure 4
Figure 5

The actual cause for this is unknown. It may be a design flaw, but it may also be attributed to certain driving or road conditions. The good news is, it’s easy to fix! The pulleys do not need to be removed to make this repair. Removing the converter housing will grant you access to the aux-trans section of the unit. This may become one of your favorite CVT transmissions too with knowing these doable fixes.

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