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.

You May Also Like

Sherlock Holmes Approach to an AB60 No-Move Situation

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult.  Using scopes provides

ab60

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult. 

GM 6T40 Pump Identification Guide

The 6T40 was introduced in 2008 for General Motors front-wheel-drive cars in the Chevrolet Malibu and has gone through several changes throughout its three generations, specifically in the pump area. The 6T40 is closely related to the more lightweight 6T30 and the heavier duty 6T45 and 6T50. Generation one started phasing out during the 2012

Seeing the Forest AND the Trees

They say that the proverbial phrase “I couldn’t see the forest for the trees” means that a person or organization cannot see the big picture because it focuses too much on the details. Related Articles – 4L60E Harsh 1-2 Shift – TASC Force Tips: Diagnosing 8L45 & 8L90 Shift Complaints – TASC Force Tips: Hydraulics

The Manifold Pipeway

The Honda six-speed transmission has been on the bench of many specialty shops for one reason or another (figure 1). But, for those of you who have yet to lay your hands on one, mounted on the upper side of the unit is one of the largest, if not the largest solenoid and pressure switch

8L90 Vacuum Testing

Below are the diagrams for vacuum testing GM 8L90 transmissions. Note: OE valves are shown in rest position and should be tested in rest position unless otherwise indicated. Test locations are pointed to with an arrow. Springs are not shown for visual clarity. A low vacuum reading indicates wear. For specific vacuum test information, refer

Other Posts

Shift Pointers: What to do when the 62TE TRS tab breaks

How frustrating it is when on a hot summer day, as you go to open a nice cold can of your drink of choice, and the tab breaks off? You are outside, away from any tools to remedy the problem quickly. It now requires a MacGyver mentality looking around at the resources available to get

Shift Pointers: Failures caused by incorrect tire sizes

For years ATSG has produced a wide range of issues related to improper tire sizes on vehicles. Even under-inflated tires have been known to cause issues. Problems such as premature failure with an active 4WD transfer case will occur with incorrect tire sizes. Related Articles – 10L80 and 10R80 pump gear differences – Top 20

Shift-Pointers-Jan-Figure-1-1400
Shift Pointers: Focused DTCs

On occasions when a vehicle’s computer system detects an error, it can set an array of diagnostic trouble codes. The variety and quantity of them require the ability to diagnose diagnostic codes, so it’s nice when codes set that point directly to the problem.  Related Articles – Going the extra mile: Proving your transmission repair suspicions

Shift pointers: High-mileage transmissions and the aches and pains of age

Among the most common four speed-transmissions keeping shops busy today are the Ford 4R70E/W, the GM 4L60-E and the GM 4L80-E. In most cases, this typically equates to working on high-mileage vehicles. Aches and pains come with age and/or high mileage. In fact, when we see a person who looks beat and tattered, some may

Shift-Pointers-November