One common complaint with the AS68RC transmission (Figure 1) is that it comes into the shop with a no-forward movement in the D range, but does move in Manual Low. This is a typical complaint of a transmission that uses a mechanical one-way clutch device on a Drive take-off that has failed.
The one-way clutch device allows for a freewheel coast. In the Manual Low position, however, a band or another set of clutches apply to provide engine breaking on coast down overriding the use of the mechanical one-way clutch. Knowing that the vehicle moves forward in Manual Low and not in Drive is indicative of this failure.
The one-way clutch device in the AS68RC transmission is called the F1 sprag (Figure 2), and it is known to fail. The good news is this sprag can be replaced without pulling the transmission.
With the transmission in the vehicle, the rear sprag can be replaced by removing the extension housing or transfer case. The output shaft or intermediate shaft and parking gear can then be removed exposing the F1 sprag for service (Figures 3 through 6).
Once a new sprag is installed, be sure that the inner race turns counterclockwise and locks clockwise. This sprag is usually installed and checked from the front of the transmission, in which case the inner race would rotate clockwise and lock counterclockwise.
The AS68RC transmission is used in Dodge diesel incomplete chassis, Isuzu cab over, Mitsubishi Fuzo and Nissan UD vehicles.
