Troubleshooting the automatic transmission is simplified by using the proven method of diagnosis. One of the most important things to remember is that there is a definite procedure to follow. Do not take short cuts or assume that critical checks or adjustments have already been made.

The following procedures are recommended for checking and/or verifying that the various components are adjusted and operating properly. Use Rotunda Automatic Transmission Tester 014-00737 or equivalent. Follow the manufacturer's instructions.

Shift Point Check—Road Test

This check will determine if the governor pressure and shift control valves are functioning properly. During the shift point check operation, if the transmission does not shift within specification or certain gear ratios cannot be obtained, refer to Diagnosis to resolve the concern.

Check shift points with engine at normal operating temperature. Operate vehicle with gear selector in the OVERDRIVE detent. The transmission should accomplish 1-2, 2-3, and 3-4 upshifts within shift speed specifications.

Shift speed specifications can be found in the Special Specifications booklet.

Improper Shift Timing—4-3 Backout Shift

Improper shift timing: 4-3 backout shift (4-3 shift on full backout of accelerator pedal, accompanied by 3-4 shift when accelerator depressed) may be diagnosed/serviced by the verification of the following:

• Loose governor: Output shaft snap ring not seated or missing locator ball
• Worn or broken output shaft seal rings, large diameter
• Worn seal ring grooves
• Worn collector bore
• Output shaft holes blocked

Forced Downshifts

With the transmission selector in OVERDRIVE, depress the accelerator pedal to the floor. The transmission should downshift to third gear or to second gear, depending on vehicle road speed. Refer to the appropriate shift speed specifications.

The transmission will not make a 4-1 downshift.

When the vehicle road speed drops below 58 km/h (35 mph), the transmission automatically downshifts from overdrive into third gear.

The transmission will not shift into fourth gear (OVERDRIVE) at wide-open throttle.

Closed Throttle Downshifts

Closed throttle downshifts should be extremely difficult to detect. It may be necessary to attach 0-690 kPa (0-100 psi) pressure gauges to the forward and direct clutch pressure taps in order to detect 4-3 and 3-2 coastdown shifts.

With gauges attached, a 4-3 coast (closed throttle), downshift is signified by the application of the forward clutch. (The pressure reading from the gauge on the forward clutch pressure tap will indicate an increase in pressure from 0-414 kPa (0-60 psi). A 3-2 coast downshift is signified by the release of the direct clutch. (The pressure reading from the gauge on the direct clutch pressure tap will indicate a decrease in pressure from 414-0 kPa (60-0 psi). A 2-1 coast downshift should not be noticed or felt. The coast downshifts should occur within the limits set forth in the shift speed specifications.

Manual Downshifts

When the shift selector is moved from either OVERDRIVE or DRIVE range to the manual LOW 1 position, the transmission will downshift into second gear if the vehicle is moving over (approximately) 41 km/h (25 mph) and into first gear if the vehicle is moving less than (approximately) 41 km/h (25 mph).

The overdrive band is applied when the transmission is in manual second. The low-reverse band is applied when the transmission is in manual LOW.