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 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:
l Loose governor: Output shaft snap ring not seated or missing locator ball
l Worn or broken output shaft seal rings, large diameter
l Worn seal ring grooves
l Worn collector bore
l 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 be imperceptible. 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.
o Harsh/Delayed 3-4 Upshift
Possible Source(s):
§ TV linkage--misadjusted/high TV/cable bent/sticking. All shifts will be harsh/delayed.
Action(s) to Take:
§ Adjust linkage. Service as required.
Possible Source(s):
§ Valve body bolts--loose/too tight.
Action(s) to Take:
§ Tighten to 9-11 N-m (80-97 lb-in).
Possible Source(s):
§ Valve body dirty/sticking valves.
Action(s) to Take:
§ Determine source of contamination. Service as required.
Possible Source(s):
§ Incorrect engine performance.
Action(s) to Take:
§ Tune/adjust engine idle as required