Tech Speaking HTML

Getting VTi Leverage

By Wayne Colonna, ATSG

Transmission Digest Technical Editor

In the July 2004 issue of Transmission Digest, a “Technically Speaking” article provided a comprehensive overview of Saturn’s CVT called the VT20/25E or VTi. Saturn used this transmission for only a short time, and now that the vehicles equipped with it have been on the road long enough to start showing up in shops for repair, technicians are getting their first look at the unit. Because of little knowledge and experience regarding this unit, a common error has developed during transmission re-assembly or valve-body replacement: incorrect indexing of the variable-ratio-control lever.

This transaxle has a bi-directional ratio-control motor (RCM) on top of the valve body (see Figure 1). The RCM indexes with a lever attached to the variable-ratio-control valve in the valve body, as Figure 2 shows. The opposite end of this lever sits inside a pocket of a device called the drive-pulley follower, as shown in Figure 3 from the valve-body case side with the valve body removed.

This spring-loaded follower rides on the movable drive-pulley half and reacts to the movement of the drive pulley as it changes ratios (see Figure 4).

With one end of the lever in the ratio-control motor and the other end in the drive-pulley follower (see Figure 5), the follower acts as a movable pivot point for the lever. In doing so, it becomes a mechanical sensor influencing the variable-ratio-control valve, tailoring the flow of feed fluid into the drive-pulley piston.

If the valve body is installed so that the lever of the variable-ratio-control valve misses the pocket of the drive-pulley follower, the valve is unable to respond to the movement of the RCM, which will prevent ratio changes of the pulleys and keep the vehicle in low range.

Fortunately, this is a simple error to correct, as the valve body is on top of the transmission, similar to its location in Saturn’s TAAT transmission. Just remove the valve body, index the lever into the pocket and re-fasten the valve body to the case. Then install the RCM, being sure that the lever sits inside the pintle pocket and not wedged between the pintle and housing. This, too, would prevent any control over the variable-ratio-control valve and keep the transmission from changing ratios.